A looming-sensitive pathway responds to changes in the trajectory of object motion.

Two identified locust neurons, the lobula giant movement detector (LGMD) and its postsynaptic partner, the descending contralateral movement detector (DCMD), constitute one motion-sensitive pathway in the visual system that responds preferentially to objects that approach on a direct collision course and are implicated in collision-avoidance behavior. Previously described responses to the approach of paired objects and approaches at different time intervals (Guest BB, Gray JR. J Neurophysiol 95: 1428-1441, 2006) suggest that this pathway may also be affected by more complicated movements in the locust's visual environment. To test this possibility we presented stationary locusts with disks traveling along combinations of colliding (looming), noncolliding (translatory), and near-miss trajectories. Distinctly different responses to different trajectories and trajectory changes demonstrate that DCMD responds to complex aspects of local visual motion. DCMD peak firing rates associated with the time of collision remained relatively invariant after a trajectory change from translation to looming. Translatory motion initiated in the frontal visual field generated a larger peak firing rate relative to object motion initiated in the posterior visual field, and the peak varied with simulated distance from the eye. Transition from translation to looming produced a transient decrease in the firing rate, whereas transition away from looming produced a transient increase. The change in firing rate at the time of transition was strongly correlated with unique expansion parameters described by the instantaneous angular acceleration of the leading edge and subtense angle of the disk. However, response time remained invariant. While these results may reflect low spatial resolution of the compound eye, they also suggest that this motion-sensitive pathway may be capable of monitoring dynamic expansion properties of objects that change the trajectory of motion.

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title: Collision judgment of objects approaching the head
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title: Multisensory Integration of Looming Signals by Rhesus Monkeys
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title: Input and Output Characteristics of Collision Avoidance Behavior in the Frog Rana catesbeiana
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title: Responses of the teleostean nucleus isthmi to looming objects and other moving stimuli
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title: Neural Representation of Object Approach in a Decision-Making Motor Circuit
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title: Escape behavior and neuronal responses to looming stimuli in the crab Chasmagnathus granulatus (Decapoda: Grapsidae)
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title: Exploitation of an Ancient Escape Circuit by an Avian Predator: Relationships between Taxon-Specific Prey Escape Circuits and the Sensitivity to Visual Cues from the Predator
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title: Collision avoidance of flying locusts: steering torques and behaviour
abstract: Obstacles approaching in the flight path trigger postural and wing kinematic adjustments in tethered flying locusts. We sought to confirm that these behaviours were steering behaviours by measuring the changes in the flight forces associated with their execution. We also investigated the coordination of these behaviours in the execution of collision avoidance manoeuvres and the effect of speed or size of the obstacle on the timing and magnitude of the response. 2. Locusts were tethered and suspended in a wind tunnel from orthogonally arranged leaf springs mounted with strain gauges. Lift and yaw torque could be monitored unambiguously. We also monitored a forward translation force which combined pitch and thrust. During flight, the locusts were videotaped from behind while targets of different sizes (5cm35 cm, 7cm37 cm, 9cm39cm, 11cm311cm) were transported towards the head at different speeds (1, 2, 3 or 4 ms21). 3. Angular asymmetry of the forewings during the downstroke with the right forewing high, and abdomen and hindleg movement to the left, were temporally associated with an increase in yaw torque to the left. With the left forewing high, abdomen and hindleg movement to the right were temporally associated with a decrease in yaw torque to the left. Obstacle avoidance behaviours could be associated with either an increase or a decrease in the pitch/thrust component. 4. Leg, abdomen and wingbeat alterations in response to the approach of an obstacle were independent but tightly coordinated. Slower approaches increased the magnitude of the responses. However, the size of the obstacle had no effect on the magnitude of the response. Slower and larger targets generated earlier reactions (i.e. locusts reacted when the targets were further from the head). 5. We conclude that the behaviours we have described were steering behaviours which would have directed the animal around an obstacle in its flight path, and that there were at least two strategies for collision avoidance associated with slowing or speeding flight. Leg, abdomen and wingbeat alterations formed a coherent avoidance response, the magnitude of which was dependent upon the time available for it to develop. We further conclude that the manoeuvre was not initiated at a constant time to collision and we propose that the avoidance strategy was to initiate the manoeuvre when the targets subtended more than 10˚ in the insect’s field of view.

title: Visual stimuli induced by self-motion and object-motion modify odour-guided flight of male moths (Manduca sexta L.)
abstract: Animals rely on multimodal sensory integration for proper orientation within their environment. For example, odour-guided behaviours often require appropriate integration of concurrent visual cues. To gain a further understanding of mechanisms underlying sensory integration in odour-guided behaviour, our study examined the effects of visual stimuli induced by self-motion and object-motion on odour-guided flight in male M. sexta. By placing stationary objects (pillars) on either side of a female pheromone plume, moths produced self-induced visual motion during odour-guided flight. These flights showed a reduction in both ground and flight speeds and inter-turn interval when compared with flight tracks without stationary objects. Presentation of an approaching 20 cm disc, to simulate object-motion, resulted in interrupted odour-guided flight and changes in flight direction away from the pheromone source. Modifications of odour-guided flight behaviour in the presence of stationary objects suggest that visual information, in conjunction with olfactory cues, can be used to control the rate of counter-turning. We suggest that the behavioural responses to visual stimuli induced by object-motion indicate the presence of a neural circuit that relays visual information to initiate escape responses. These behavioural responses also suggest the presence of a sensory conflict requiring a trade-off between olfactory and visually driven behaviours. The mechanisms underlying olfactory and visual integration are discussed in the context of these behavioural responses.

title: Responses of descending neurons to looming stimuli in the praying mantis Tenodera aridifolia
abstract: Responses to visual stimuli of some neurons that descend the nerve cord from the brain were recorded extracellularly in the mantis Tenodera aridifolia. Most of the recorded neurons showed their largest responses to looming stimuli that simulated a black circle approaching towards the mantis. The neurons showed a transient excitatory response to a gradually darkening or receding circle. The neurons showed sustained excitation to the linearly expanding stimuli, but the spike frequency decreased rapidly. The responses of the neurons were affected by both the diameter and the speed of looming stimuli. Faster or smaller looming stimuli elicited a higher peak frequency. These responses were observed in both recordings from the connective between suboesophageal and prothoracic ganglia and the connective between prothoracic and mesothoracic ganglia. There was a one-to-one correspondence of spike firing between these two recordings with a fixed delay. The neurons had the receptive field on ipsilateral side to its axon at the cervical connective. These results suggest that there is a looming-sensitive descending neuron, with an axon projecting over prothoracic ganglion, in the mantis nervous system.

title: Multiplicative computation in a visual neuron sensitive to looming
abstract: Multiplicative operations are important in sensory processing, but their biophysical implementation remains largely unknown. We investigated an identified neuron (the lobula giant movement detector, LGMD, of locusts) whose output firing rate in response to looming visual stimuli has been described by two models, one of which involves a multiplication. In this model, the LGMD multiplies postsynaptically two inputs (one excitatory, one inhibitory) that converge onto its dendritic tree; in the other model, inhibition is presynaptic to the LGMD. By using selective activation and inactivation of pre- and postsynaptic inhibition, we show that postsynaptic inhibition has a predominant role, suggesting that multiplication is implemented within the neuron itself. Our pharmacological experiments and measurements of firing rate versus membrane potential also reveal that sodium channels act both to advance the response of the LGMD in time and to map membrane potential to firing rate in a nearly exponential manner. These results are consistent with an implementation of multiplication based on dendritic subtraction of two converging inputs encoded logarithmically, followed by exponentiation through active membrane conductances.

title: Spatial distribution of inputs and local receptive field properties of a wide-field, looming sensitive neuron.
abstract: The lobula giant movement detector (LGMD) in the locust visual system and its target neuron, the descending contralateral movement detector (DCMD), respond to approaching objects looming on a collision course with the animal. They thus provide a good model to study the cellular and network mechanisms underlying the sensitivity to this specific class of behaviorally relevant stimuli. We determined over an entire locust eye the density distribution of optical axes describing the spatial organization of local inputs to the visual system and compared it with the sensitivity distribution of the LGMD/DCMD to local motion stimuli. The density of optical axes peaks in the equatorial region of the frontal eye. Local motion sensitivity, however, peaks in the equatorial region of the caudolateral visual field and only correlates positively with the dorso-ventral density of optical axes. On local stimulation, both the velocity tuning and the response latency of the LGMD/DCMD depend on stimulus position within the visual field. Spatial and temporal integration experiments in which several local motion stimuli were activated either simultaneously or at fixed delays reveal that the LGMD processes local motion in a strongly sublinear way. Thus the neuron's integration properties seem to depend on several factors including its dendritic morphology, the local characteristics of afferent fiber inputs, and inhibition mediated by different pathways or by voltage-gated conductances. Our study shows that the selectivity of this looming sensitive neuron to approaching objects relies on more complex biophysical mechanisms than previously thought.

title: Orientation of flying locusts, Schistocerca gregaria (Forsk.), in migrating swarms
abstract: In eastern Africa between 1951 and 1955 and in south-western Morocco in 1960, orientations and densities of flying locusts in migrating swarms of Schistocerca gregaria Forsk. were recorded photographically, with supplementary visual observations. The densities ranged from 0·0006 to 1·23 locusts/m 3 (mean spacing between nearest locusts 12 and 1 m, respectively) with a median value of 0·024 locusts/m 3 ; in 50% of the samples mean spacing was 2–4 m, suggesting a preferred distance of that order. The orientations were affected by gregarious reactions to neighbouring fliers, and to locusts in a mass. In the swarms there was a preponderance of streaming groups in which locusts headed in the same general direction; in about half of these groups the angular deviation about the mean orientation was only ±20°. In comparatively dense swarms the orientations of the lower fliers in the interiors of swarms were diverse and random in relation to wind and to the swarm track. But at the leading, the trailing and the lateral edges they were predominantly into the swarm, as the result of observed changes of headings back towards the swarm in locusts flying out beyond the main mass. The orientations of locusts photographed at about 100 m and 200–400 m above the ground were found to be predominantly in the direction of the swarm track, i.e. , with wind; it is suggested that they arose from compensatory optomotor responses to retinal velocities of substrate patterns, and are consistent with Kennedy's hypothesis of optomotor orientation to wind. Among lower-flying locusts such responses appeared to become important in diffuse formations and in strong winds. Thus flight on consistently into-wind courses was repeatedly seen in low-flying diffuse formations of sexually mature locusts migrating in light winds. In stronger winds the orientations of lower fliers in all types of swarms suggested responses to unacceptable retinal velocities, which interfered with the into-the-swarm orientations on the swarm edges; the continued cohesion of swarms may thus require a wind profile in which they are not evoked below a certain level. In persistent strong wind in excess of locusts' air speeds, flight activity was reduced, and swarms exhibited low into-wind flight by locusts in small numbers. It is suggested that the characteristic downwind tracks of discrete immature swarms are set primarily by the downwind orientations of their higherflying members. In sexually mature swarms the downwind displacements are probably performed mainly by the denser and the higher-rising swarms, while the into-wind flights of low diffuse formations would slow down movement, and could result in limited displacement up-wind.

title: WING MOVEMENTS ASSOCIATED WITH COLLISIONAVOIDANCE MANOEUVRES DURING FLIGHT IN THE LOCUST LOCUSTA MIGRATORIA
abstract: Flying locusts will try to avoid colliding with objects directly in their flight path. This study investigated the wing movements and behaviour patterns associated with collision avoidance. 2. Tethered locusts were flown in a wind tunnel. Targets were transported at different speeds either directly towards the head of the animal or to one side of the midline but parallel to it. Changes in the form of the wingbeat for each of the wings were monitored using either a video camera or a high-speed cine camera. 3. Animals attempted to avoid an impending collision by making movements interpreted here as (a) increasing lift to fly over the object, (b) gliding and extending the forelegs to land on the object, and (c) steering to one side of the object. Steering was monitored by observation of abdominal movements. 4. Steering to one side of an approaching target was reliably associated with an earlier and more pronounced pronation of the wings on the inside of the turn. Also, in the middle of the downstroke, the forewings were markedly asymmetrical. On the outside of the turn, the forewing was more elevated and separate from the hindwing. On the inside of the turn, the forewing was more depressed and often came down in conjunction with, or in advance of, the hindwing on that side. 5. The forewing asymmetry correlated with the position of the target such that most attempted turns were in the direction that would take the animal around the closest edge. High-speed cinematography showed that the asymmetry was caused both by changes in the timing of the two wings and by changes in the angular ranges of the wingbeats. 6. We propose that these changes in the form and timing of the wingbeats are likely to have swung the flight force vector around the long axis of the body to produce a banked turn around the closest edge of the object.

title: Role of an identified looming-sensitive neuron in triggering a flying locust's escape.
abstract: Flying locusts perform a characteristic gliding dive in response to predator-sized stimuli looming from one side. These visual looming stimuli trigger trains of spikes in the descending contralateral movement detector (DCMD) neuron that increase in frequency as the stimulus gets nearer. Here we provide evidence that high-frequency (>150 Hz) DCMD spikes are involved in triggering the glide: the DCMD is the only excitatory input to a key gliding motor neuron during a loom; DCMD-mediated EPSPs only summate significantly in this motor neuron when they occur at >150 Hz; when a looming stimulus ceases approach prematurely, high-frequency DCMD spikes are removed from its response and the occurrence of gliding is reduced; and an axon important for glide triggering descends in the nerve cord contralateral to the eye detecting a looming stimulus, as the DCMD does. DCMD recordings from tethered flying locusts showed that glides follow high-frequency spikes in a DCMD, but analyses could not identify a feature of the DCMD response alone that was reliably associated with glides in all trials. This was because, for a glide to be triggered, the high-frequency spikes must be timed appropriately within the wingbeat cycle to coincide with wing elevation. We interpret this as flight-gating of the DCMD response resulting from rhythmic modulation of the flight motor neuron's membrane potential during flight. This means that the locust's escape behavior can vary in response to the same looming stimulus, meaning that a predator cannot exploit predictability in the locust's collision avoidance behavior.

title: Multiplexing of Motor Information in the Discharge of a Collision Detecting Neuron during Escape Behaviors
abstract: Locusts possess an identified neuron, the descending contralateral movement detector (DCMD), conveying visual information about impending collision from the brain to thoracic motor centers. We built a telemetry system to simultaneously record, in freely behaving animals, the activity of the DCMD and of motoneurons involved in jump execution. Cocontraction of antagonistic leg muscles, a required preparatory phase, was triggered after the DCMD firing rate crossed a threshold. Thereafter, the number of DCMD spikes predicted precisely motoneuron activity and jump occurrence. Additionally, the time of DCMD peak firing rate predicted that of jump. Ablation experiments suggest that the DCMD, together with a nearly identical ipsilateral descending neuron, is responsible for the timely execution of the escape. Thus, three distinct features that are multiplexed in a single neuron's sensory response to impending collision-firing rate threshold, peak firing time, and spike count-probably control three distinct motor aspects of escape behaviors.

title: Motor activity and trajectory control during escape jumping in the locust Locusta migratoria
abstract: We investigated the escape jumps that locusts produce in response to approaching objects. Hindleg muscular activity during an escape jump is similar to that during a defensive kick. Locusts can direct their escape jumps up to 50° either side of the direction of their long axis at the time of hindleg flexion, allowing them to consistently jump away from the side towards which an object is approaching. Variation in jump trajectory is achieved by rolling and yawing movements of the body that are controlled by the fore- and mesothoracic legs. During hindleg flexion, a locust flexes the foreleg ipsilateral to its eventual jump trajectory and then extends the contralateral foreleg. These foreleg movements continue throughout co-contraction of the hindleg tibial muscles, pivoting the locust’s long axis towards its eventual jump trajectory. However, there are no bilateral differences in the motor programs of the left and right hindlegs that correlate with jump trajectory. Foreleg movements enable a locust to control its jump trajectory independent of the hindleg motor program, allowing a decision on jump trajectory to be made after the hindlegs have been cocked in preparation for a jump.

title: The locust DCMD, a movement-detecting neurone tightly tuned to collision trajectories
abstract: A Silicon Graphics computer was used to challenge the locust descending contralateral movement detector (DCMD) neurone with images of approaching objects. The DCMD gave its strongest response, measured as either total spike number or spike frequency, to objects approaching on a direct collision course. Deviation in either a horizontal or vertical direction from a direct collision course resulted in a reduced response. The decline in the DCMD response with increasing deviation from a collision course was used as a measure of the tightness of DCMD tuning for collision trajectories. Tuning was defined as the half-width of the response when it had fallen to half its maximum level. The response tuning, measured as averaged mean spike number versus deviation away from a collision course, had a half-width at half-maximum response of 2.4 °­3.0 ° for a deviation in the horizontal direction and 3.0 ° for a deviation in the vertical direction. Mean peak spike frequency showed an even sharper tuning, with a half-width at half-maximum response of 1.8 ° for deviations away from a collision course in the horizontal plane.

title: Response of the locust descending movement detector neuron to rapidly approaching and withdrawing visual stimuli
abstract: Preliminary observations on five female desert locusts, Schistocerca gregaria (Forskal), reveal particularly vigorous response in the descending contralateral (DCMD) movement detector neurons to bl...

title: Orthopteran DCMD neuron: a reevaluation of responses to moving objects. II. Critical cues for detecting approaching objects.
abstract: 1. We examine the critical image cues that are used by the locust visual system for the descending contralateral motion detector (DCMD) neuron to distinguish approaching from receding objects. Images were controlled by computer and presented on an electrostatic monitor. 2. Changes in overall luminance elicited much smaller and briefer responses from the DCMD than objects that appeared to approach the eye. Although a decrease in overall luminance might boost the response to an approaching dark object, movement of edges of the image is more important. 3. When two pairs of lines, in a cross-hairs configuration, were moved apart and then together again, the DCMD showed no preference for divergence compared with convergence of edges. A directional response was obtained by either making the lines increase in extent during divergence and decrease in extent during convergence; or by continually increasing the velocity of line movement during divergence and decreasing velocity during convergence. 4. The DCMD consistently gave a larger response to growing than to shrinking solid rectangular images. An increase compared with a decrease in the extent of edge in an image is, therefore, an important cue for the directionality of the response. For single moving edges of fixed extent, the neuron gave the largest response to edges that subtended 15 degrees at the eye. 5. The DCMD was very sensitive to the amount by which an edge traveled between frames on the display screen, with the largest responses generated by 2.5 degrees of travel. This implies that the neurons in the optic lobe that drive this movement-detecting system have receptive fields of about the same extent as a single ommatidium. 6. For edges moving up to 250 degree/s, the excitation of the DCMD increases with velocity. The response to an edge moving at a constant velocity adapts rapidly, in a manner that depends on velocity. Movement over one part of the retina can adapt the subsequent response to movement over another part of the retina. 7. For the DCMD to track and continue to respond to the image of an approaching object, the edges of the image must continually increase in velocity. This is the second important stimulus cue. 8. Edges of opposite contrasts (light-dark compared with dark-light) are processed in separate pathways that inhibit each other. This would contribute to the reduction of responses to wide-field movements.

title: Escapes with and without preparation: the neuroethology of visual startle in locusts.
abstract: Locusts respond to the images of approaching (looming) objects with responses that include gliding while in flight and jumping while standing. For both of these responses there is good evidence that the DCMD neuron (descending contralateral movement detector), which carries spike trains from the brain to the thoracic ganglia, is involved. Sudden glides during flight, which cause a rapid loss of height, are last-chance manoeuvres without prior preparation. Jumps from standing require preparation over several tens of milliseconds because of the need to store muscle-derived energy in a catapult-like mechanism. Locusts' DCMD neurons respond selectively to looming stimuli, and make connections with some motor neurons and interneurons known to be involved in flying and jumping. For glides, a burst of high-frequency DCMD spikes is a key trigger. For jumping, a similar burst can influence timing, but neither the DCMD nor any other single interneuron has been shown to be essential for triggering any stage in preparation or take-off. Responses by the DCMD to looming stimuli can alter in different behavioural contexts: in a flying locust, arousal ensures a high level of both DCMD responsiveness and glide occurrence; and there are significant differences in DCMD activity between locusts in the gregarious and the solitarious phase.

title: Intracellular characterization of neurons in the locust brain signaling impending collision.
abstract: 1. In response to a rapidly approaching object, intracellular recordings show that excitation in the locust lobula giant movement detecting (LGMD) neuron builds up exponentially, particularly during the final stages of object approach. After the cessation of object motion, inhibitory potentials in the LGMD then help to terminate this excitation. Excitation in the LGMD follows object recession with a short, constant latency but is cut back rapidly by hyperpolarizing potentials. The timing of these hyperpolarizing potentials in the LGMD is variable, and their latency following object recession is shortest with the highest velocities of motion simulated. The hyperpolarizing potentials last from 50-300 ms and are often followed by re-excitation. The observed hyperpolarizations of the LGMD can occur without any preceding excitation and are accompanied by a measurable conductance increase. The hyperpolarizations are likely to be inhibitory postsynaptic potentials (PSPs). The behavior of the intracellularly recorded inhibitory PSPs (IPSPs) closely parallels that of the feed forward inhibitory loop in the neural network described by Rind and Bramwell. 2. The preference of the LGMD for approaching versus receding objects remains over a wide range of starting and finishing distances. The response to object approach, measured both as membrane potential and spike rate, remains single peaked with starting distances of between 200 and 2,100 mm, and approach speeds of 0.5-2 m/s. These results confirm the behavior predicted by the neural network described by Rind and Bramwell but contradicts the findings of Rind and Simmons, forcing a re-evaluation of the suitability of some of the mechanical visual stimuli used in that study. 3. For depolarization of the LGMD neuron to be maintained or increased throughout the motion of image edges, the edges must move with increasing velocity over the eye. Membrane potential declines before the end of edge motion with constant velocities of edge motion. 4. A second identified neuron, the LGMD2 also is shown to respond directionally to approaching objects. In both the LGMD and LGMD2 neurons, postsynaptic inhibition shapes the directional response to object motion.

title: A chemical synapse between two motion detecting neurones in the locust brain.
abstract: The LGMD is the major source of visual input from the compound eye to the ipsilateral DCMD. Inactivating the LGMD or hyperpolarizing it, so it no longer spikes, abolishes the response of the DCMD to the visual stimulus. Synaptic transmission between the LGMD and DCMD neurones is chemical. A spike in the LGMD terminals induces a postsynaptic potential in the DCMD dendrites, with a transmission delay of 1 ms. There is a conductance increase in the DCMD during an LGMD-mediated PSP. The conductance increase occurs at membrane potentials when the current/voltage relationship of the DCMD membrane is linear, and at several different membrane potentials. The LGMD-mediated PSP within the dendritic region of the DCMD has a rise time of 1.3 ms, a half-time for decay of 2.2 ms and a total duration of 8.3 ms. In the cell body it has a rise time of 3.3 ms, a half-time for decay of 8 ms and a total duration of 21.3 ms. The amplitude of the LGMD-mediated PSP depends on the membrane potential of the DCMD. The PSP amplitude is increased by membrane hyperpolarization and decreased by membrane depolarizations. At a membrane potential 30 mV more positive than resting potential the extrapolated size of the PSP is zero. The synaptic efficiency of the LGMD-DCMD connection is usually 1.2. (formula; see text) There is a threshold of 13 mV in the LGMD before synaptic transmission occurs. Currents less than 13 mV are not transmitted in either direction across the synapse although they do reach the synaptic region if they are injected at the extremities of the neurones within the brain. Length constants for the LGMD are 0.36 mm between points c and d in the protocerebrum and 0.63 mm between point b in the optic lobe and point d in the protocerebrum. The length constant measured between the dendrite region of the DCMD and its cell body is 1.34 mm. DCMD spikes and PSPs follow spikes in the LGMD at a constant latency at frequencies up to 400 Hz. Usually a spike in the LGMD induces a spike in the DCMD.

title: Connections between descending visual interneurons and metathoracic motoneurons in the locust
abstract: SummaryConnections between the four DMD neurons and metathoracic motoneurons in the locustSchistocerca were examined by recording extracellularly from the interneurons in the pro-mesothoracic connectives and intracellularly from seventeen motoneurons. A DIMD or DCMD spike causes an EPSP in the fast extensor tibiae motoneuron, which can be modified by changing the membrane potential. The EPSP always follows spikes at frequencies up to 200 Hz and with a latency of 0.9 ms, suggesting that the connections are monosynaptic and chemically mediated. EPSPs from the DIMD or DCMD arrive at the same time, their axons having the same conduction velocity, and appear simultaneously in the fast extensor tibiae motoneurons on both sides of the ganglion. There is spatial and temporal summation between the inputs but on no occasion did the motoneurons spike. Three inhibitory neurons are depolarized by DMD inputs and may on occasion spike, but it is not known whether these connections are direct. Similarly the slow excitatory motoneuron to the anterior coxal adductor muscle is hyperpolarized by DMD input. Other leg, flight or ventilatory motoneurons examined received no inputs from the DMD neurons. The connections shown are consistent with the hypothesis that the DMD neurons are in some way involved with initiation of a jump, but to achieve this must act synergistically with other inputs.

title: Heterogeneous properties of segmentally homologous interneurons in the ventral nerve cord of locusts
abstract: The G, B1, and B2 neurons are three prominent interneurons located in adjacent segmental ganglia in the central nervous system of locusts. Previous studies on the adult nervous system have shown that each of these cells has its own distinctive morphology and responsiveness to auditory input. Previous studies on the embryonic nervous system have described the lineage and development of one of these cells, the G neuron, in the mesothoracic (T2) segment. In this paper it is shown that the G, B1, and B2 neurons are segmental homologues in that they arise from equivalent lineages during embryogenesis in the T2, T3, and A1 segments, respectively. Each cell arises (along with its identified sibling neuron) from the division of the second ganglion mother cell of neuroblast 7–4. The segment‐specific morphology of the G homologues was determined in the T3 and A1 segments between 60–70% of embryonic development, and their identity was established as the adult B1 and B2 neurons by comparing the distinctive cell‐specific features of their morphology between embryo and adult. Although all three neurons display striking morphological differences, they all share certain structural features in common, including the location of their primary axons and neurites in specific tracts in the neuropil.

title: Connexions between a movement-detecting visual interneurone and flight motoneurones of a locust.
abstract: Both of the descending contralateral movement detector (DCMD) neurones of Schistocerca americana gregaria, which respond to stimulation of the contralateral eye or to loud noises, mediate excitatory postsynaptic potentials in most ipsilateral flight motoneurones.

title: Vision Egg: an Open-Source Library for Realtime Visual Stimulus Generation
abstract: Modern computer hardware makes it possible to produce visual stimuli in ways not previously possible. Arbitrary scenes, from traditional sinusoidal gratings to naturalistic 3D scenes can now be specified on a frame-by-frame basis in realtime. A programming library called the Vision Egg that aims to make it easy to take advantage of these innovations. The Vision Egg is a free, open-source library making use of OpenGL and written in the high-level language Python with extensions in C. Careful attention has been paid to the issues of luminance and temporal calibration, and several interfacing techniques to input devices such as mice, movement tracking systems, and digital triggers are discussed. Together, these make the Vision Egg suitable for many psychophysical, electrophysiological, and behavioral experiments. This software is available for free download at visionegg.org.

title: The separation of visual axes in apposition compound eyes.
abstract: Measurements of the interommatidial angle (Δ ϕ ) and facet diameter ( D ) of the same ommatidia in a number of insects and crustaceans with large eyes have been related to the effective intensity at which the eye functions by the following theory. The highest spatial frequency which the eye is able to reconstruct as a pattern is limited by the interommatidial angle Δ ϕ , Which is the sampling angle, because two ommatidia are required to cover each cycle of the pattern. At the same time, the absolute modutlation of light in the receptors caused by the pattern depends on three interdependent factors. ( a ) The theoretical minimum angular sensitivity function, which has a width of θ/ D at the 50% level. The wavelength θ is taken as 0.5 μm. This component is not only the limiting angular resolving power of the lens: it reduces modulation caused by all patterns, with greater loss at higher spatial frequencies. Larger lenses increase resolution and sensitivity. ( b ) The effective light catching area of the rhabdom. This is the angular subtense of the rhabdom area (the receptor) as seen in the outside world (i.e. subtended through the posterior nodal point of the lens), and is the equivalent of the grain size in a film. Large receptors favour sensitivity at the expense of resolution.  From this, the optimum value of the product D Δ ϕ (known as the eye parameter) can be calculated for eyes adapted to any ambient intensity. The same result is reached by a recent theory of Snyder, Stavenga & Laughlin (1977) who calculate the value of D Δ ϕ which allows the eye to reconstruct the maximum number of pictures despite photon noise. The eye parameter (divided by half the wavelength) is the ratio of the highest spatiai frequency passing the lens to the highest spatial frequency reconstructed by the eye. Compound eyes should have larger facets and interommatidial angles than predicted by diffraction theory alone because photon noise must be exceeded at all intensities. Theoretically, D Δ ϕ lies in the range 0.3 to 0.5 for bright light insects and is increased to 2.0 or more for those active in dim light. As well as depending on intensity, D Δ ϕ should depend on factors such as the typical angular velocity and level of intensity discrimination at which the eye is used. As D Δ ϕ can be measured from the outside of the eye, the theoretical predictions can be compared with measured values. Most of this paper consists of maps of the values of D Δ ϕ for eyes of a variety of arthropods from different habitats. The maps are made by a new convention in which the minimum theoretical field of each ommatidium is placed in angular coordinates as a circle of diameter θ/ D with centre on the axis at the place where it lies on the eye. To do this, a value of θ must be assumed. Every fifth facet is taken on most maps with the fields magnified five times. The overlap or separation of these circles of diameter θ/ D shows the local value of D Δ ϕ for any direction for each part of the eye. The method is independent of horizontal and vertical axes, of directions of facet rows, of regularity of facets and of eye radius. The problem of mapping a surface with double curvature upon a flat sheet was solved approximately by working with strips taken along the eye surface. Equal distances on the map then represent equal angles in any direction; with this projection there are no poles, and axes are arbitrary. Maps of D Δ ϕ reveal that compound eyes differ according to the intensity of light they normally encounter; eyes of animals which are active in bright light have smaller values of D Δ ϕ . The smallest value of about 0.3 is found in the forward facing acute zone of the sand wasp Bembix , which hovers while hunting in bright sunshine. The absolute limit set by diffraction of 0.25 (for square facets) is approached but never reached. Values of D Δ ϕ up to about 2.0 or even 4.0 are found in crepuscular animals which have apposition eyes. The interpretation is that the values of D and Δ ϕ are the result of a compromise between contrast sensitivity and resolution. An increase in aperture provides increased modulation and therefore increased sensitivity, but the additional angular resolving power which comes with the increased aperture is not used because sensitivity is also enhanced by an increase in the receptor size. The ommatidium then detects only the lower spatial frequencies (wider stripes) from the range which passes the lens. In an ommatidium optimized for any but the highest known intensities, both Δ ϕ and D (and therefore D Δ ϕ ) are larger than they would have to be if set at the diffraction limit. The maps also reveal that many apposition compound eyes have one or more regions of smaller Δ ϕ , called acute zones. None of the eyes are spherically symmetrical; all have gradients of both D and Δ ϕ , and all have regions where Δ ϕ varies in different directions on the eye surface. The acute zone is usually forward looking, but is upward looking in some insects which catch prey or mate in flight. In addition, some dragonflies have a lateral acute zone. In the acute zone the facet pattern is always more regular than elsewhere. Some acute zones, as in the locust ( Locusta ), the mantid Orthodera and the ghost crab Ocypode , are formed by reduction in Δ ϕ with little compensatory increase in D . Others such as the native bee Amegila , the dragonfly Austrogomphus , and the mantid shrimp Odontodactylus have larger values of D which match the decreasing Δ ϕ towards the centre of the acute zone, so that D Δ ϕ remains constant. Others again, particularly the wasp Bembix , the dragonflies Hemicordulia, Orthetrum and several mantids, show an increase in D which is insufficient to compensate for the large decrease in Δ ϕ , so that D Δ ϕ is smaller in the acute zone. A reduced D Δ ϕ in the acute zone may imply that it requires brighter light or more time than the rest of the eye in order to make full use of its increased sampling density. Mapping the regional differences of the theoretical resolving power of the ommatidia, and of the potential spatial resolution of different parts of the eye is only the first step towards understanding the functions of the different eye regions. The anatomical basis of the optics, the actual field sizes of receptors as measured physiologically, the part played by binocular overlap, the regional differences in the mechanisms of integration behind the eye, and the patterns of behaviour that are dependent on each eye region, remain to be elucidated.

title: Retinal image size triggers obstacle avoidance in flying locusts
abstract: d8 99 + + 335 568 y w 25-w 1-y 1-362 568 meiotic recombination between the two Y's can practically be excluded; it lies definitely under 2 %. The possibility of X-Y recombination in female meiosis has also been tested. The 362 male offspring of In(1)sc4LscSR,y sc4scSw/In(1)sc 4L scSR,y sc4scSw/w+W y+ $ 9 x wild-type d d showed the expected genotypes  with the exception of two recombinants that, again, most probably result from exchange between one of the X's and a euchromatic section within the w+Y y+ chromosome. Mitotic recombination has been induced by treating larvae 42-44 h after egg deposition with X-rays (100 kV, 8 mA, FD 10 cm, 1.7 mm Al-filter, exposure time 1.5 rain, corresponding to 1480 _+ 20 R); or with mitomycin C (1.5 ml 1.2 mM mitomycin C in 0.5 % saccharose solution, 2.5 h feeding time). Three days after hatching adults were inspected for single and twin mosaic spots in their eyes. Control recombination frequencies depend upon the distance between cen-tromere and marker, in our case almost the whole length of the X-chromosome; they lie below 0.5 % . On the y+Y map chromosome see [7, 8], on zeste see .

title: Computation of Object Approach by a Wide-Field, Motion-Sensitive Neuron
abstract: The lobula giant motion detector (LGMD) in the locust visual system is a wide-field, motion-sensitive neuron that responds vigorously to objects approaching the animal on a collision course. We investigated the computation performed by LGMD when it responds to approaching objects by recording the activity of its postsynaptic target, the descending contralateral motion detector (DCMD). In each animal, peak DCMD activity occurred a fixed delay δ (15 ≤ δ ≤ 35 msec) after the approaching object had reached a specific angular threshold θthres on the retina (15° ≤ θthres ≤ 40°). θthres was independent of the size or velocity of the approaching object. This angular threshold computation was quite accurate: the error of LGMD and DCMD in estimating θthres(3.1–11.9°) corresponds to the angular separation between two and six ommatidia at each edge of the expanding object on the locust retina. It was also resistant to large amplitude changes in background luminosity, contrast, and body temperature. Using several experimentally derived assumptions, the firing rate of LGMD and DCMD could be shown to depend on the product ψ(t − δ) · e−αθ(t−δ), where θ(t) is the angular size subtended by the object during approach, ψ(t) is the angular edge velocity of the object and the constant, and α is related to the angular threshold size [α = 1/tan(θthres/2)]. Because LGMD appears to receive distinct input projections, respectively motion- and size-sensitive, this result suggests that a multiplication operation is implemented by LGMD. Thus, LGMD might be an ideal model to investigate the biophysical implementation of a multiplication operation by single neurons.

title: Habituated visual neurons in locusts remain sensitive to novel looming objects
abstract: Many animals must contend with visual cues that provide information about the spatiotemporal dynamics of multiple objects in their environment. Much research has been devoted to understanding how an identified pair of interneurons in the locust, the Descending Contralateral Movement Detectors (DCMDs), respond to objects on an impending collision course. However, little is known about how these neurons respond when challenged with multiple, looming objects of different complex shapes. I presented locusts with objects resembling either another locust or a bird approaching on a direct collision course at 3 m s-1 while recording from the DCMD axon within the mesothoracic ganglion. Stimulus presentations were designed to test: (i) whether DCMD habituation was related to the frequency of approach, (ii) if habituated DCMDs were able to respond to a novel stimulus and (iii) if non-looming motion within complex objects (internal object motion) during approach affects habituation. DCMD responses to simulated locusts or birds habituated more when the time interval between consecutive approaches within similar sequences decreased from 34 s to 4 s. Strongly habituated DCMDs were, however, able to respond to the same object approaching along a new trajectory or to a larger object approaching along the same trajectory. Habituation was not affected by internal object motion. These data are consistent with earlier findings that DCMD habituation occurs at localized synapses, which permits maintained sensitivity to multiple objects in the animal's environment.

title: Activity of descending contralateral movement detector neurons and collision avoidance behaviour in response to head-on visual stimuli in locusts
abstract: We recorded the activity of the right and left descending contralateral movement detectors responding to 10-cm (small) or 20-cm (large) computer-generated spheres approaching along different trajectories in the locust's frontal field of view. In separate experiments we examined the steering responses of tethered flying locusts to identical stimuli. The descending contralateral movement detectors were more sensitive to variations in target trajectory in the horizontal plane than in the vertical plane. Descending contralateral movement detector activity was related to target trajectory and to target size and was most sensitive to small objects converging on a direct collision course from above and to one side. Small objects failed to induce collision avoidance manoeuvres whereas large objects produced reliable collision avoidance responses. Large targets approaching along a converging trajectory produced steering responses that were either away from or toward the side of approach of the object, whereas targets approaching along trajectories that were offset from the locust's mid-longitudinal body axis primarily evoked responses away from the target. We detected no differences in the discharge properties of the descending contralateral movement detector pair that could account for the different collision avoidance behaviours evoked by varying the target size and trajectories. We suggest that descending contralateral movement detector properties are better suited to predator evasion than collision avoidance.

title: Orthopteran DCMD neuron: a reevaluation of responses to moving objects. I. Selective responses to approaching objects.
abstract: 1. The "descending contralateral movement detector" (DCMD) neuron in the locust has been challenged with a variety of moving stimuli, including scenes from a film (Star Wars), moving disks, and images generated by computer. The neuron responds well to any rapid movement. For a dark object moving along a straight path at a uniform velocity, the DCMD gives the strongest response when the object travels directly toward the eye, and the weakest when the object travels away from the eye. Instead of expressing selectivity for movements of small rather than large objects, the DCMD responds preferentially to approaching objects. 2. The neuron shows a clear selectivity for approach over recession for a variety of sizes and velocities of movement both of real objects and in simulated movements. When a disk that subtends > or = 5 degrees at the eye approaches the eye, there are two peaks in spike rate: one immediately after the start of movement; and a second that builds up during the approach. When a disk recedes from the eye, there is a single peak in response as the movement starts. There is a good correlation between spike rate and angular acceleration of the edges of the image over the eye. 3. When an object approaches from a distance sufficient for it to subtend less than one interommatidial angle at the start of its approach, there is a single peak in response. The DCMD tracks the approach, and, if the object moves at 1 m/s or faster, the spike rate increases throughout the duration of object movement. The size of the response depends on the speed of approach. 4. It is unlikely that the DCMD encodes the time to collision accurately, because the response depends on the size as well as the velocity of an approaching object. 5. Wide-field movements suppress the response to an approaching object. The suppression varies with the temporal frequency of the background pattern. 6. Over a wide range of contrasts of object against background, the DCMD gives a stronger response to approaching than to receding objects. For low contrasts, the selectivity is greater for objects that are darker than the background than for objects that are lighter.

title: Invariance of Angular Threshold Computation in a Wide-Field Looming-Sensitive Neuron
abstract: The lobula giant motion detector (LGMD) is a wide-field bilateral visual interneuron in North American locusts that acts as an angular threshold detector during the approach of a solid square along a trajectory perpendicular to the long axis of the animal (Gabbiani et al., 1999a). We investigated the dependence of this angular threshold computation on several stimulus parameters that alter the spatial and temporal activation patterns of inputs onto the dendritic tree of the LGMD, across three locust species. The same angular threshold computation was implemented by LGMD in all three species. The angular threshold computation was invariant to changes in target shape (from solid squares to solid discs) and to changes in target texture (checkerboard and concentric patterns). Finally, the angular threshold computation did not depend on object approach angle, over at least 135° in the horizontal plane. A two-dimensional model of the responses of the LGMD based on linear summation of motion-related excitatory and size-dependent inhibitory inputs successfully reproduced the experimental results for squares and discs approaching perpendicular to the long axis of the animal. Linear summation, however, was unable to account for invariance to object texture or approach angle. These results indicate that LGMD is a reliable neuron with which to study the biophysical mechanisms underlying the generation of complex but invariant visual responses by dendritic integration. They also suggest that invariance arises in part from non-linear integration of excitatory inputs within the dendritic tree of the LGMD.

title: Spatiotemporal receptive field properties of a looming-sensitive neuron in solitarious and gregarious phases of the desert locust.
abstract: Desert locusts (Schistocerca gregaria) can transform reversibly between the swarming gregarious phase and a solitarious phase, which avoids other locusts. This transformation entails dramatic changes in morphology, physiology, and behavior. We have used the lobula giant movement detector (LGMD) and its postsynaptic target, the descending contralateral movement detector (DCMD), which are visual interneurons that detect looming objects, to analyze how differences in the visual ecology of the two phases are served by altered neuronal function. Solitarious locusts had larger eyes and a greater degree of binocular overlap than those of gregarious locusts. The receptive field to looming stimuli had a large central region of nearly equal response spanning 120 degrees x 60 degrees in both phases. The DCMDs of gregarious locusts responded more strongly than solitarious locusts and had a small caudolateral focus of even further sensitivity. More peripherally, the response was reduced in both phases, particularly ventrally, with gregarious locusts showing greater proportional decrease. Gregarious locusts showed less habituation to repeated looming stimuli along the eye equator than did solitarious locusts. By contrast, in other parts of the receptive field the degree of habituation was similar in both phases. The receptive field organization to looming stimuli contrasts strongly with the receptive field organization of the same neurons to nonlooming local-motion stimuli, which show much more pronounced regional variation. The DCMDs of both gregarious and solitarious locusts are able to detect approaching objects from across a wide expanse of visual space, but phase-specific changes in the spatiotemporal receptive field are linked to lifestyle changes.

title: Precise Subcellular Input Retinotopy and Its Computational Consequences in an Identified Visual Interneuron
abstract: The Lobula Giant Movement Detector (LGMD) is a higher-order visual interneuron of Orthopteran insects that responds preferentially to objects approaching on a collision course. It receives excitatory input from an entire visual hemifield that anatomical evidence suggests is retinotopic. We show that this excitatory projection activates calcium-permeable nicotinic acetylcholine receptors. In vivo calcium imaging reveals that the excitatory projection preserves retinotopy down to the level of a single ommatidium. Examining the impact of retinotopy on the LGMD's computational properties, we show that sublinear synaptic summation can explain orientation preference in this cell. Exploring retinotopy's impact on directional selectivity leads us to infer that the excitatory input to the LGMD is intrinsically directionally selective. Our results show that precise retinotopy has implications for the dendritic integration of visual information in a single neuron.

title: Spike-frequency adaptation and intrinsic properties of an identified, looming-sensitive neuron.
abstract: We investigated in vivo the characteristics of spike-frequency adaptation and the intrinsic membrane properties of an identified, looming-sensitive interneuron of the locust optic lobe, the lobula giant movement detector (LGMD). The LGMD had an input resistance of 4-5 MOmega, a membrane time constant of about 8 ms, and exhibited inward rectification and rebound spiking after hyperpolarizing current pulses. Responses to depolarizing current pulses revealed the neuron's intrinsic bursting properties and pronounced spike-frequency adaptation. The characteristics of adaptation, including its time course, the attenuation of the firing rate, the mutual dependency of these two variables, and their dependency on injected current, closely followed the predictions of a model first proposed to describe the adaptation of cat visual cortex pyramidal neurons in vivo. Our results thus validate the model in an entirely different context and suggest that it might be applicable to a wide variety of neurons across species. Spike-frequency adaptation is likely to play an important role in tuning the LGMD and in shaping the variability of its responses to visual looming stimuli.

title: Spike frequency adaptation mediates looming stimulus selectivity in a collision-detecting neuron
abstract: How active membrane conductance dynamics tunes neurons for specific time-varying stimuli remains poorly understood. We studied the biophysical mechanisms by which spike frequency adaptation shapes visual stimulus selectivity in an identified visual interneuron of the locust. The lobula giant movement detector (LGMD) responds preferentially to objects approaching on a collision course with the locust. Using calcium imaging, pharmacology and modeling, we show that spike frequency adaptation in the LGMD is mediated by a Ca2+-dependent potassium conductance closely resembling those associated with 'small-conductance' (SK) channels. Intracellular block of this conductance minimally affected the LGMD's response to approaching stimuli, but substantially increased its response to translating ones. Thus, spike frequency adaptation contributes to the neuron's tuning by selectively decreasing its responses to nonpreferred stimuli. Our results identify a new mechanism by which spike frequency adaptation may tune visual neurons to behaviorally relevant stimuli.

title: Complex spike activity of Purkinje cells in the ventral uvula and nodulus of pigeons in response to translational optic flow.
abstract: The complex spike (CS) activity of Purkinje cells in the ventral uvula and nodulus of the vestibulocerebellum was recorded from anesthetized pigeons in response to translational optic flow. Translational optic flow was produced using a "translator" projector: a mechanical device that projected a translational optic flowfield onto the walls, ceiling, and floor of the room and encompassed the entire binocular visual field. CS activity was broadly tuned but maximally modulated in response to translational optic flow along a "best" axis. Each neuron was assigned a vector representing the direction in which the animal would need to translate to produce the optic flowfield that resulted in maximal excitation. The vector is described with reference to a standard right-handed coordinate system, where the vectors, +x, +y, and +z represent, rightward, upward, and forward translation of the animal, respectively. Neurons could be grouped into four response types based on the vector of maximal excitation. +y neurons were modulated maximally in response to a translational optic flowfield that results from self-motion upward along the vertical (y) axis. -y neurons also responded best to translational optic flow along the vertical axis but showed the opposite direction preference. The two remaining groups responded best to translational optic flow along horizontal axes: -x + z neurons and -x-z neurons. In summary, our results suggest that the olivocerebellar system dedicated to the analysis of translational optic flow is organized according to a reference frame consisting of three approximately orthogonal axes: the vertical axis, and two horizontal axes oriented 45 degrees to either side the midline. Previous research has shown that the rotational optic flow system, the eye muscles, the vestibular semicircular canals and the postural control system all share a similar spatial frame of reference.

title: A DIRECTIONALLY SELECTIVE MOTION-DETECTING NEURONE IN THE BRAIN OF THE LOCUST : PHYSIOLOGICAL AND MORPHOLOGICAL CHARACTERIZATION
abstract: 1. The anatomy and physiology of a directionally selective motion-detecting (DSMD) neurone in the locust are described. The neurone was descending, with the cell body in the protocerebrum. The axon lay in the dorsolateral quadrant of the nerve cord and has been traced as far as the metathoracic ganglion. It arborized, ipsilateral to the cell body, from the dorsal intermediate tract (DIT) in the suboesophageal and thoracic ganglia. 2. The neurone was binocular and sensitive to motion in the horizontal plane. It had a preferred direction backwards over the ipsilateral eye and forwards over the contralateral eye. Motion in the opposite direction suppressed the discharge, which had a frequency of 5-20 spikes s" at resting membrane potential. 3. The neurone showed a clear directional response to stimuli with temporal frequencies between 0.7 and 44Hz, with a peak response at 11-22 Hz. It responded with spikes to light ON and light OFF. 4. The neurone responded directionally to spatial frequencies of 0.28 cycles degree" (3.7° stripe period) to above 0.025 cycles degree" (40° stripe period). The maximum response was at around 0.035 cycles degree" (29° stripe period). 5. No evidence of adaptation was seen in the responses of the neurone to real or apparent continuous horizontal motion in either the preferred or the null direction.

title: Neural networks in the cockpit of the fly
abstract: Flies have been buzzing around on earth for over 300 million years. During this time they have radiated into more than 125,000 different species (Yeates and Wiegmann 1999), so that, by now, roughly every tenth described species is a fly. They thus represent one of the most successful animal groups on our planet. This evolutionary success might, at least in part, be a result of their acrobatic maneuverability, which enables them, for example, to chase mates at turning velocities of more than 3000° s–1 with delay times of less than 30 ms (Land and Collett 1974; Wagner 1986). It is this fantastic behavior, which has initiated much research during the last decades, both on its sensory control and the biophysical and aerodynamic principles of the flight output (Dickinson et al. 1999, 2000). Here, we review the current state of knowledge about the neural processing of visual motion, which represents one sensory component intimately involved in flight control. Other reviews on this topic have been published with a similar (Hausen 1981, 1984; Hausen and Egelhaaf 1989; Borst 1996) or different emphasis (Frye and Dickinson 2001; Borst and Dickinson 2002). Because of space limitations, we do not review the extensive work that has been done on fly motion-sensitive neurons to advance our understanding of neural coding (Bialek et al. 1991; Rieke et al. 1997; de Ruyter et al. 1997, 2000; Haag and Borst 1997, 1998; Borst and Haag 2001). Unless stated otherwise, all data presented in the following were obtained on the blowfly Calliphora vicina which we will often casually refer to as 'the fly'.

title: Neural network based on the input organization of an identified neuron signaling impending collision.
abstract: 1. We describe a four-layered neural network , based on the input organization of a collision signaling neuron in the visual system of the locust, the lobula giant movement detector (LGMD). The 250 photoreceptors ("P" units) in layer 1 are excited by any change in illumination, generated when an image edge passes over them. Layers 2 and 3 incorporate both excitatory and inhibitory interactions, and layer 4 consists of a single output element, equivalent to the locust LGMD. 2. The output element of the neural network, the "LGMD", responds directionally when challenged with approaching versus receding objects, preferring approaching objects (Figs. 2-4). The time course and shape of the "LGMD" response matches that of the LGMD . Directionality is maintained with objects of various sizes and approach velocities. The network is tuned to direct approach . The "LGMD" shows no directional selectivity for translatory motion at a constant velocity across the "eye", but its response increases with edge velocity (Figs. 6 and 9). 3. The critical image cues for a selective response to object approach by the "LGMD" are edges that change in extent or in velocity as they move . Lateral inhibition is crucial to the selectivity of the "LGMD" and the selective response is abolished or else much reduced if lateral inhibition is taken out of the network . We conclude that lateral inhibition in the neuronal network for the locust LGMD also underlies the experimentally observed critical image cues for its directional response. 4. Lateral inhibition shapes the velocity tuning of the network for objects moving in the X and Y directions without approaching the eye . As an edge moves over the eye at a constant velocity, a race occurs between the excitation that is caused by edge movement and which passes down the network and the inhibition that passes laterally. Excitation must win this race for units in layer 3 to reach threshold  The faster the edge moves over the eye the more units in layer 3 reach threshold and pass excitation on to the "LGMD" . 5. Lateral inhibition shapes the tuning of the network for objects moving in the Z direction, toward or away from the eye . As an object approaches the eye there is a buildup of excitation in the "LGMD" throughout the movement whereas the response to object recession is often brief, particularly for high velocities. During object motion, a critical race occurs between excitation passing down the network and inhibition directed laterally, excitation must win this race for the rapid buildup in excitation in the "LGMD" as seen in the final stages of object approach (Figs. 10-12). The buildup is eliminated if, during object approach, excitation cannot win this race (as happens when the spread of inhibition laterally takes < 1 ms Fig. 13, D and E). Taking all lateral inhibition away increases the "LGMD" response to object approach, but overall directional selectivity is reduced as there is also a lot of residual network excitation following object recession . 6. Directional selectivity for rapidly approaching objects is further enhanced at the level of the "LGMD" by the timing of a feed-forward, inhibitory loop onto the "LGMD", activated when a large number of receptor units are excited in a short time. The inhibitory loop is activated at the end of object approach, truncating the excitatory "LGMD" response after approach has ceased, but at the initiation of object recession (. Eliminating the feed-forward, inhibitory loop prolongs the "LGMD" response to both receding and approaching objects .

title: Seeing what is coming: building collision-sensitive neurones
abstract: The image of a rapidly approaching object has to elicit a quick response. An animal needs to know that the object is approaching on a collision course and how imminent a collision is. The relevant information can be computed from the way that the image of the object grows on the retina of one eye. Firm data about the types of neurones that react to such looming stimuli and trigger avoidance reactions come from recent studies on the pigeon and the locust. The neurones responsible are tightly tuned to detect objects that are approaching on a direct collision course. In the pigeon these neurones signal the time remaining before collision whereas in the locust they have a crucial role in the simple strategy this animal uses to detect an object approaching on a collision course.

title: A fly-locust based neuronal control system applied to an unmanned aerial vehicle: the invertebrate neuronal principles for course stabilization, altitude control and collision avoidance
abstract: The most versatile and robust flying machines are still those produced by nature through evolution. The solutions to the 6 DOF control problem faced by these machines are implemented in extremely small neuronal structures comprising thousands of neurons. Hence, the biological principles of flight control are not only very effective but also efficient in terms of their implementation. An important question is to what extent these principles can be generalized to man-made flying platforms. Here, this question is investigated in relation to the computational and behavioral principles of the opto-motor system of the fly and locust. The aim is to provide a control infrastructure based only on biologically plausible and realistic neuronal models of the insect opto-motor system. It is shown that relying solely on vision, biologically constrained neuronal models of the fly visual system suffice for course stabilization and altitude control of a blimp-based UAV. Moreover, the system is augmented with a collision avoidance model based on the Lobula Giant Movement Detector neuron of the Locust. It is shown that the biologically constrained course stabilization model is highly robust and that the combined model is able to perform autonomous indoor flight.

title: A modified model for the Lobula Giant Movement Detector and its FPGA implementation
abstract: Bio-inspired vision sensors are particularly appropriate candidates for navigation of vehicles or mobile robots due to their computational simplicity, allowing compact hardware implementations with low power dissipation. The Lobula Giant Movement Detector (LGMD) is a wide-field visual neuron located in the Lobula layer of the Locust nervous system. The LGMD increases its firing rate in response to both the velocity of an approaching object and the proximity of this object. It has been found that it can respond to looming stimuli very quickly and trigger avoidance reactions. It has been successfully applied in visual collision avoidance systems for vehicles and robots. This paper introduces a modified neural model for LGMD that provides additional depth direction information for the movement. The proposed model retains the simplicity of the previous model by adding only a few new cells. It has been simplified and implemented on a Field Programmable Gate Array (FPGA), taking advantage of the inherent parallelism exhibited by the LGMD, and tested on real-time video streams. Experimental results demonstrate the effectiveness as a fast motion detector.

title: Reactive direction control for a mobile robot: a locust-like control of escape direction emerges when a bilateral pair of model locust visual neurons are integrated
abstract: Locusts possess a bilateral pair of uniquely identifiable visual neurons that respond vigorously to the image of an approaching object. These neurons are called the lobula giant movement detectors (LGMDs). The locust LGMDs have been extensively studied and this has lead to the development of an LGMD model for use as an artificial collision detector in robotic applications. To date, robots have been equipped with only a single, central artificial LGMD sensor, and this triggers a non-directional stop or rotation when a potentially colliding object is detected. Clearly, for a robot to behave autonomously, it must react differently to stimuli approaching from different directions. In this study, we implement a bilateral pair of LGMD models in Khepera robots equipped with normal and panoramic cameras. We integrate the responses of these LGMD models using methodologies inspired by research on escape direction control in cockroaches. Using ‘randomised winner-take-all’ or ‘steering wheel’ algorithms for LGMD model integration, the Khepera robots could escape an approaching threat in real time and with a similar distribution of escape directions as real locusts. We also found that by optimising these algorithms, we could use them to integrate the left and right DCMD responses of real jumping locusts offline and reproduce the actual escape directions that the locusts took in a particular trial. Our results significantly advance the development of an artificial collision detection and evasion system based on the locust LGMD by allowing it reactive control over robot behaviour. The success of this approach may also indicate some important areas to be pursued in future biological research.

title: Sensory neural codes using multiplexed temporal scales
abstract: Determining how neuronal activity represents sensory information is central for understanding perception. Recent work shows that neural responses at different timescales can encode different stimulus attributes, resulting in a temporal multiplexing of sensory information. Multiplexing increases the encoding capacity of neural responses, enables disambiguation of stimuli that cannot be discriminated at a single response timescale, and makes sensory representations stable to the presence of variability in the sensory world. Thus, as we discuss here, temporal multiplexing could be a key strategy used by the brain to form an information-rich and stable representation of the environment.

title: A multi-stage anti-predator response increases information on predation risk
abstract: Optimal escape theory generally assumes that animals have accurate information about predator distance and direction of approach. To what degree such information is available depends not only on the prey's sensory capabilities but also on its behaviour. The structure of behaviour can strongly constrain or support the gathering of information. The ability of animals to collect and process information is therefore an important factor shaping predator avoidance strategies. Fiddler crabs, like many prey animals, escape predators in a multi-step sequence. In their initial response, they do not have accurate information about a predator's distance and approach trajectory and are forced to base their response decision on incomplete information that is not strictly correlated with risk. We show here that fiddler crabs gather qualitatively different visual information during successive stages of their escape sequence. This suggests that multi-stage anti-predator behaviours serve not only to successively reduce risk but also to increase the quality of information with regards to the actual risk. There are countless reasons why prey animals are not able to accurately assess risk. By concentrating on sensory limitations, we can quantify such information deficits and investigate how improving risk assessment helps prey optimise the balance between predation risk and escape costs.

title: Synchronized Neural Input Shapes Stimulus Selectivity in a Collision-Detecting Neuron
abstract: How higher-order sensory neurons generate complex selectivity from their simpler inputs is a fundamental question in neuroscience. The lobula giant movement detector (LGMD) is such a visual neuron in the locust Schistocerca americana that responds selectively to objects approaching on a collision course or their two-dimensional projections, looming stimuli [1-4]. To study how this selectivity arises, we designed an apparatus allowing us to stimulate, individually and independently, a sizable fraction of the ∼15,000 elementary visual inputs impinging retinotopically onto the LGMD's dendritic fan [5-7]  We then recorded intracellularly in vivo throughout the visual pathway, assessing the LGMD's activity and that of all three successive presynaptic stages conveying local excitatory inputs. Our results suggest that as collision becomes increasingly imminent, the strength of these inputs increases, whereas their latency decreases. This latency decrease favors summation of inputs activated sequentially throughout the looming sequence, making the neuron maximally sensitive to collision-bound trajectories. Thus, the LGMD's selectivity arises partially from presynaptic mechanisms that synchronize a large population of inputs during a looming stimulus and subsequent detection by postsynaptic mechanisms within the neuron itself. Analogous mechanisms are likely to underlie the tuning properties of visual neurons in other species as well.

title: A pair of motion-sensitive neurons in the locust encode approaches of a looming object
abstract: Neurons in the locust visual system encode approaches of looming stimuli and are implicated in production of escape behaviours. The lobula giant movement detector (LGMD) and its postsynaptic partner, the descending contralateral movement detector (DCMD) compute characteristics of expanding edges across the locust eye during a loom and DCMD synapses onto motor elements associated with behaviour. We identified another descending interneuron within the locust ventral nerve cord. We named this neuron the late DCMD (LDCMD) as it responds later during an approach, with the firing rate peaking at about the time of collision. LDCMD produced lower amplitude, broader action potentials that were associated with an afterhyperpolarization, whereas DCMD action potentials showed a brief afterhyperpolarization often followed by an afterdepolarization. Within the mesothoracic ganglion, the primary LDCMD axon located adjacent to the DCMD axon, was thinner and lacked collateral projections to the lateral region of the neuropil. When compared with DCMD, LDCMD fired with fewer spikes during a loom and showed weaker habituation to repeated approaches. Coincidence of LDCMD and DCMD firing increased during object approach. Our findings indicate the presence of an additional motion-sensitive descending neuron in the locust that encodes temporally distinct properties of an approaching object.

title: Organization and significance of neurons that detect change of visual depth in the hawk moth Manduca sexta
abstract: Visual stimuli representing looming or receding objects can be decomposed into four parameters: change in luminance; increase or decrease of area; increase or decrease of object perimeter length; and motion of the object's perimeter or edge. This paper describes intracellular recordings from visual neurons in the optic lobes of Manduca sexta that are selectively activated by certain of these parameters. Two classes of wide‐field neurons have been identified that respond selectively to looming and receding stimuli. Class 1 cells respond to parameters of the image other than motion stimuli. They discriminate an approaching or receding disc from an outwardly or inwardly rotating spiral, being activated only by the disc and not by the spiral. Class 2 neurons respond to moving edges. They respond both to movement of the spiral and to an approaching or receding disc. These two classes are further subdivided into neurons that are excited by image expansion (looming) and are inhibited by image contraction (antilooming). Class 2 neurons also respond to horizontal and vertical movement of gratings over the retina. Stimulating class 1 and 2 neurons with white discs against a dark background results in the same activation as stimulation with dark discs against a white background, demonstrating that changes in luminance play no role in the detection of looming or antilooming. The present results show that the two types of looming‐sensitive neurons in M. sexta use different mechanisms to detect the approach or retreat of an object. It is proposed that cardinal parameters for this are change of perimeter length detected by class 1 neurons and expansion or contraction visual flow fields detected by class 2 neurons. These two classes also differ with respect to their polarity, the former comprising centripetal cells from the optic lobes to the midbrain, the latter comprising centrifugal neurons from the midbrain to the optic lobes. The significance of these arrangements with respect to hovering flight is discussed.  2000.

title: Visual system of the european hummingbird hawkmoth Macroglossum stellatarum (sphingidae, lepidoptera): Motion‐sensitive interneurons of the lobula plate
abstract: The European hummingbird hawkmoth Macroglossum stellatarum is a member of the sphingid family, denoted by their ability to hover in place in front of flowers. The fast and acrobatic flight behavior is thought to be under the control of the optomotor system both during normal, forward flight and during stationary, hovering flight. Electrophysiologic and neuroanatomic studies presented here reveal large‐field, motion‐sensitive neurons in the lobula plate. Anatomic and physiologic features characterize these nerve cells as horizontal and vertical motion‐sensitive neurons. Horizontal cells react best to horizontal movement of vertical gratings moving in either direction and show no response to vertically moving horizontal gratings. The dendritic arborizations of horizontal cells are found characteristically in the two outer layers of the lobula plate. In contrast, vertical cells react best to upward or downward motion of horizontal gratings. They are not sensitive to horizontal‐moving gratings. The dendritic arborizations of the vertical cells are restricted to the two innermost lobula plate layers. These anatomic and physiologic features, as well as a number of other characteristics, such as tonic responses and cosine‐shaped tuning curves, are most reminiscent of neurons that comprise the horizontal and vertical systems described from the fly, thus suggesting comparable roles in the control of optomotor behavior. The present study also identifies a small group of neurons that exhibit phasic responses and reactions to specific orientations of the pattern. These cells are discussed with regard to their possible roles in control tasks, such as edge‐orientation detection or the detection of sudden displacements of the visual surround.   1999.

title: A descending contralateral directionally selective movement detector in the praying mantis Tenodera aridifolia
abstract: Extracellular recordings were made from a directionally selective neuron in the ventral nerve cord of mantises. The neuron’s preferred direction of motion was forward and upward over the compound eye contralateral to its axon at the cervical connective. The neuron was sensitive to wide-field motion stimuli, resistant to habituation, and showed transient excitation in response to light ON and OFF stimuli. Its responses to drifting gratings depended on the temporal frequency and contrast of the stimulus. These results suggest that the neuron receives input from correlation-type motion detectors.