bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of Network Activities on Neuronal Properties in Corticothalamic Systems
Authors: Steriade M.
Published: December 2017

Data from in vivo and in vitro experiments are discussed to emphasize that synaptic activities in neocortex and thalamus have a decisive impact on intrinsic neuronal properties in intact-brain preparations under anesthesia and even more so during natural states of vigilance. Thus the firing patterns of cortical neuronal types are not inflexible but may change with the level of membrane potential and during periods rich in synaptic activity. The incidences of some cortical cell classes (defined by their responses to depolarizing current pulses) are different in isolated cortical slabs in vivo or in slices maintained in vitro compared with the intact cortex of naturally awake animals. Network activities, which include the actions of generalized modulatory systems, have a profound influence on the membrane potential, apparent input resistance, and backpropagation of action potentials. The analysis of various oscillatory types leads to the conclusion that in the intact brain, there are no “pure” rhythms, generated in simple circuits, but complex wave sequences (consisting of different, low- and fast-frequency oscillations) that result from synaptic interactions in corticocortical and corticothalamic neuronal loops under the control of activating systems arising in the brain stem core or forebrain structures. As an illustration, it is shown that the neocortex governs the synchronization of network or intrinsically generated oscillations in the thalamus. The rhythmic recurrence of spike bursts and spike trains fired by thalamic and cortical neurons during states of decreased vigilance may lead to plasticity processes in neocortical neurons. If these phenomena, which may contribute to the consolidation of memory traces, are not constrained by inhibitory processes, they induce seizures in which the neocortex initiates the paroxysms and controls their thalamic reflection. The results indicate that intact-brain preparations are necessary to investigate global brain functions such as behavioral states of vigilance and paroxysmal activities.
Learning Increases Stimulus Salience in Anterior Inferior Temporal Cortex of the Macaque
Authors: Jagadeesh Bharathi , Chelazzi Leonardo , Mishkin Mortimer , Desimone Robert
Published: December 2017

With experience, an object can become behaviorally relevant and thereby quickly attract our interest when presented in a visual scene. A likely site of these learning effects is anterior inferior temporal (aIT) cortex, where neurons are thought to participate in the filtering of irrelevant information out of complex visual displays. We trained monkeys to saccade consistently to one of two pictures in an array, in return for a reward. The array was constructed by pairing two stimuli, one of which elicited a good response from the cell when presented alone (“good” stimulus) and the other of which elicited a poor response (“poor” stimulus). The activity of aIT cells was recorded while monkeys learned to saccade to either the good or poor stimulus in the array. We found that neuronal responses to the array were greater (before the saccade occurred) when training reinforced a saccade to the good stimulus than when training reinforced a saccade to the poor stimulus. This difference was not present on incorrect trials, i.e., when saccades to the incorrect stimulus were made. Thus the difference in activity was correlated with performance. The response difference grew over the course of the recording session, in parallel with the improvement in performance. The response difference was not preceded by a difference in the baseline activity of the cells, unlike what was found in studies of cued visual search and working memory in aIT cortex. Furthermore, we found similar effects in a version of the task in which any of 10 possible pairs of stimuli, prelearned before the recording session, could appear on a given trial, thereby precluding a working memory strategy. The results suggest that increasing the behavioral significance of a stimulus through training alters the neural representation of that stimulus in aIT cortex. As a result, neurons responding to features of the relevant stimulus may suppress neurons responding to features of irrelevant stimuli.
Temporal Frequency of Whisker Movement. II. Laminar Organization of Cortical Representations
Authors: Ahissar Ehud , Sosnik Ronen , Bagdasarian Knarik , Haidarliu Sebastian
Published: December 2017

Part of the information obtained by rodent whiskers is carried by the frequency of their movement. In the thalamus of anesthetized rats, the whisker frequency is represented by two different coding schemes: by amplitude and spike count (i.e., response amplitudes and spike counts decrease as a function of frequency) in the lemniscal thalamus and by latency and spike count (latencies increase and spike counts decrease as a function of frequency) in the paralemniscal thalamus (see accompanying paper). Here we investigated neuronal representations of the whisker frequency in the primary somatosensory (“barrel”) cortex of the anesthetized rat, which receives its input from both the lemniscal and paralemniscal thalamic nuclei. Single and multi-units were recorded from layers 2/3, 4 (barrels only), 5a, and 5b during vibrissal stimulation. Typically, the input frequency was represented by amplitude and spike count in the barrels of layer 4 and in layer 5b (the “lemniscal layers”) and by latency and spike count in layer 5a (the “paralemniscal layer”). Neurons of layer 2/3 displayed a mixture of the two coding schemes. When the pulse width of the stimulus was reduced from 50 to 20 ms, the latency coding in layers 5a and 2/3 was dramatically reduced, while the spike-count coding was not affected; in contrast, in layers 4 and 5b, the latencies remained constant, but the spike counts were reduced with 20-ms stimuli. The same effects were found in the paralemniscal and lemniscal thalamic nuclei, respectively (see accompanying paper). These results are consistent with the idea that thalamocortical loops of different pathways, although terminating within the same cortical columns, perform different computations in parallel. Furthermore, the mixture of coding schemes in layer 2/3 might reflect an integration of lemniscal and paralemniscal outputs.
Acetylcholine-Dependent Induction and Expression of Functional Plasticity in the Barrel Cortex of the Adult Rat
Authors: Ego-Stengel Valérie , Shulz Daniel E. , Haidarliu Sebastian , Sosnik Ronen , Ahissar Ehud
Published: December 2017

The involvement of acetylcholine (ACh) in the induction of neuronal sensory plasticity is well documented. Recently we demonstrated in the somatosensory cortex of the anesthetized rat that ACh is also involved in the expression of neuronal plasticity. Pairing stimulation of the principal whisker at a fixed temporal frequency with ACh iontophoresis induced potentiations of response that required re-application of ACh to be expressed. Here we fully characterize this phenomenon and extend it to stimulation of adjacent whiskers. We show that these ACh-dependent potentiations are cumulative and reversible. When several sensori-cholinergic pairings were applied consecutively with stimulation of the principal whisker, the response at the paired frequency was further increased, demonstrating a cumulative process that could reach saturation levels. The potentiations were specific to the stimulus frequency: if the successive pairings were done at different frequencies, then the potentiation caused by the first pairing was depotentiated, whereas the response to the newly paired frequency was potentiated. During testing, the potentiation of response did not develop immediately on the presentation of the paired frequency during application of ACh: the analysis of the kinetics of the effect indicates that this process requires the sequential presentation of several trains of stimulation at the paired frequency to be expressed. We present evidence that a plasticity with similar characteristics can be induced for responses to stimulation of an adjacent whisker, suggesting that this potentiation could participate in receptive field spatial reorganizations. The spatial and temporal properties of the ACh-dependent plasticity presented here impose specific constraints on the underlying cellular and molecular mechanisms.
Paradoxical Reduction of Synaptic Inhibition by Vigabatrin
Authors: Overstreet Linda S. , Westbrook Gary L.
Published: December 2017

GABAergic inhibition, a primary target for pharmacological modulation of excitability in the CNS, can be altered by multiple mechanisms including alteration of GABA metabolism. Gamma-vinyl GABA (vigabatrin, GVG) is an irreversible inhibitor of the GABA catabolic enzyme GABA transaminase, thus its anticonvulsant properties are thought to result from an elevation of brain GABA levels. We examined the effects of GVG on GABAergic synaptic transmission in hippocampal slices. GVG unexpectedly reduced miniature and evoked inhibitory postsynaptic currents (IPSCs) in dentate granule cells. The reduction in synaptic events was accompanied by an increase in tonic GABAA receptor–mediated current. These effects developed slowly and persisted following wash out of GVG. The GVG pretreatment reduced sucrose-evoked GABA release as well as postsynaptic sensitivity to exogenous GABA, indicating that both pre- and postsynaptic mechanisms contributed to the reduction in synaptic currents. These results suggest that tonic rather than phasic increases in GABA underlie the anticonvulsant properties of GVG, and that mechanisms that elevate brain neurotransmitter levels do not necessarily correlate with enhanced synaptic release.
Recruitment of Cat Motoneurons in the Absence of Homonymous Afferent Feedback
Authors: Haftel Valerie K. , Prather Jonathan F. , Heckman C. J. , Cope Timothy C.
Published: December 2017

This study provides the first test in vivo of the hypothesis that group Ia muscle-stretch afferents aid in preventing reversals in the orderly recruitment of motoneurons. This hypothesis was tested by studying recruitment of motoneurons deprived of homonymous afferent input. Recruitment order was measured in decerebrate, paralyzed cats from dual intra-axonal records obtained simultaneously from pairs of medial gastrocnemius (MG) motoneurons. Pairs of MG motor axons were recruited in eight separate trials of the reflex discharge evoked by stimulation of the caudal cutaneous sural (CCS) nerve. Some reports suggest that reflex recruitment by this cutaneous input should bias recruitment against order by the size principle in which the axon with the slower conduction velocity (CV) in a pair is recruited to fire before the faster CV axon. Recruitment was studied in three groups of cats: ones with the MG nerve intact and untreated (UNTREATED); ones with the MG nerve cut (CUT); and ones with the MG nerve cut and bathed at its proximal end in lidocaine solution (CUT+). The failure of electrical stimulation to initiate a dorsal root volley and the absence of action potentials in MG afferents demonstrated the effective elimination of afferent feedback in the CUT+ group. Recruitment order by the size principle predominated and was not statistically distinguishable among the three groups. The percentage of pairs recruited in reverse order of the size principle was actually smaller in the CUT+ group (6%) than in CUT (15%) or UNTREATED (19%) groups. Thus homonymous afferent feedback is not necessary to prevent recruitment reversal. However, removing homonymous afferent input did result in the expression of inconsistency in order, i.e., switches in recruitment sequence from one trial to the next, for more axon pairs in the CUT+ group (33%) than for the other groups combined (13%). Increased inconsistency in the absence of increased reversal of recruitment order was approximated in computer simulations by increasing time-varying fluctuations in synaptic drive to motoneurons and could not be reproduced simply by deleting synaptic current from group Ia homonymous afferents, regardless of how that current was distributed to the motoneurons. These findings reject the hypothesis that synaptic input from homonymous group Ia afferents is necessary to prevent recruitment reversals, and they are consistent with the assertion that recruitment order is established predominantly by properties intrinsic to motoneurons.
Active Locomotion Increases Peak Firing Rates of Anterodorsal Thalamic Head Direction Cells
Authors: Zugaro Michaël B. , Tabuchi Eiichi , Fouquier Céline , Berthoz Alain , Wiener Sidney I.
Published: December 2017

Head direction (HD) cells discharge selectively in macaques, rats, and mice when they orient their head in a specific (“preferred”) direction. Preferred directions are influenced by visual cues as well as idiothetic self-motion cues derived from vestibular, proprioceptive, motor efferent copy, and command signals. To distinguish the relative importance of active locomotor signals, we compared HD cell response properties in 49 anterodorsal thalamic HD cells of six male Long-Evans rats during active displacements in a foraging task as well as during passive rotations. Since thalamic HD cells typically stop firing if the animals are tightly restrained, the rats were trained to remain immobile while drinking water distributed at intervals from a small reservoir at the center of a rotatable platform. The platform was rotated in a clockwise/counterclockwise oscillation to record directional responses in the stationary animals while the surrounding environmental cues remained stable. The peak rate of directional firing decreased by 27% on average during passive rotations ( r 2 = 0.73, P< 0.001). Individual cells recorded in sequential sessions ( n = 8) reliably showed comparable reductions in peak firing, but simultaneously recorded cells did not necessarily produce identical responses. All of the HD cells maintained the same preferred directions during passive rotations. These results are consistent with the hypothesis that the level of locomotor activity provides a state-dependent modulation of the response magnitude of AD HD cells. This could result from diffusely projecting neuromodulatory systems associated with motor state.
Experimental and Computational Analysis of Monkey Smooth Pursuit Eye Movements
Authors: Churchland Mark M. , Lisberger Stephen G.
Published: December 2017

Smooth pursuit eye movements are guided by visual feedback and are surprisingly accurate despite the time delay between visual input and motor output. Previous models have reproduced the accuracy of pursuit either by using elaborate visual signals or by adding sources of motor feedback. Our goal was to constrain what types of signals drive pursuit by obtaining data that would discriminate between these two modeling approaches, represented by the “image motion model” and the “tachometer feedback” model. Our first set of experiments probed the visual properties of pursuit with brief square-pulse and sine-wave perturbations of target velocity. Responses to pulse perturbations increased almost linearly with pulse amplitude, while responses to sine wave perturbations showed strong saturation with increasing stimulus amplitude. The response to sine wave perturbations was strongly dependent on the baseline image velocity at the time of the perturbation. Responses were much smaller if baseline image velocity was naturally large, or was artificially increased by superimposing sine waves on pulse perturbations. The image motion model, but not the tachometer feedback model, could reproduce these features of pursuit. We used a revision of the image motion model that was, like the original, sensitive to both image velocity and image acceleration. Due to a saturating nonlinearity, the sensitivity to image acceleration declined with increasing image velocity. Inclusion of this nonlinearity was motivated by our experimental results, was critical in accounting for the responses to perturbations, and provided an explanation for the unexpected stability of pursuit in the presence of perturbations near the resonant frequency. As an emergent property, the revised image motion model was able to reproduce the frequency and damping of oscillations recorded during artificial feedback delays. Our second set of experiments replicated prior recordings of pursuit responses to multiple-cycle sine wave perturbations, presented over a range of frequencies. The image motion model was able to reproduce the responses to sine wave perturbations across all frequencies, while the tachometer feedback model failed at high frequencies. These failures resulted from the absence of image acceleration signals in the tachometer model. We conclude that visual signals related to image acceleration are important in driving pursuit eye movements and that the nonlinearity of these signals provides stability. Smooth pursuit thus illustrates that a plausible neural strategy for combating natural delays in sensory feedback is to employ information about the derivative of the sensory input.
Enhanced Responses of Spinal Dorsal Horn Neurons to Heat and Cold Stimuli Following Mild Freeze Injury to the Skin
Authors: Khasabov Sergey G. , Cain David M. , Thong Dinh , Mantyh Patrick W. , Simone Donald A.
Published: December 2017

The effects of a mild freeze injury to the skin on responses of nociceptive dorsal horn neurons to cold and heat stimuli were examined in anesthetized rats. Electrophysiological recordings were obtained from 72 nociceptive spinal neurons located in the superficial and deep dorsal horn. All neurons had receptive fields (RFs) on the glabrous skin of the hindpaw, and neurons were functionally divided into wide dynamic range (WDR) and high-threshold (HT) neurons. Forty-four neurons (61%) were classified as WDR and responded to both innocuous and noxious mechanical stimuli (mean mechanical threshold of 12.8 ± 1.6 mN). Twenty-eight neurons (39%) were classified as HT and were excited only by noxious mechanical stimuli (mean mechanical threshold of 154.2 ± 18.3 mN). Neurons were characterized for their sensitivity heat (35 to 51°C) and cold (28 to −12°C) stimuli applied to their RF. Among WDR neurons, 86% were excited by both noxious heat and cold stimuli, while 14% responded only to heat. For HT neurons, 61% responded to heat and cold stimuli, 32% responded only to noxious heat, and 7% responded only to noxious cold. Effects of a mild freeze injury (−15°C applied to the RF for 20 s) on responses to heat and cold stimuli were examined in 30 WDR and 22 HT neurons. Skin freezing was verified as an abrupt increase in skin temperature at the site of injury due to the exothermic reaction associated with crystallization. Freezing produced a decrease in response thresholds to heat and cold stimuli in most WDR and HT neurons. WDR and HT neurons exhibited a mean decrease in response threshold for cold of 9.0 ± 1.3°C and 10.0 ± 1.6°C, respectively. Mean response thresholds for heat decreased 4.0 ± 0.4°C and 4.3 ± 1.3°C in WDR and HT neurons, respectively. In addition, responses to suprathreshold cold and heat stimuli increased. WDR and HT neurons exhibited an 89% and a 192% increase in response across all cold stimuli, and a 93 and 92% increase in responses evoked across all heat stimuli, respectively. Our results demonstrate that many spinal neurons encode intensity of noxious cold as well as noxious heat over a broad range of stimulus temperatures. Enhanced responses of WDR and HT neurons to cold and heat stimuli after a mild freeze injury is likely to contribute to thermal hyperalgesia following a similar freeze injury in humans.
Reflex and Intrinsic Changes Induced by Fatigue of Human Elbow Extensor Muscles
Authors: Zhang Li-Qun , Rymer W. Zev
Published: December 2017

Fatigue-induced changes in intrinsic and reflex properties of human elbow extensor muscles and the underlying mechanisms for fatigue compensation were investigated. The elbow joint was perturbed using small-amplitude and pseudorandom movement patterns while subjects maintained steady levels of mean joint extension torque. Intrinsic and reflex properties were identified simultaneously using a nonlinear delay differential equation model. Intrinsic joint properties were characterized by measures of joint stiffness, viscous damping, and limb inertia and reflex properties characterized by measures of dynamic and static reflex gains. Fatigue was induced using 15 min of intermittent voluntary isometric (submaximal) exercise, and a rest period of 10 min was taken to allow the fatigued muscles torecover from acute fatigue effects. Identical experimental and data analysis procedures were used before and after fatigue. Our findings were that after fatigue, joint stiffness was significantly reduced at higher torque levels, presumably reflecting the reduced force-generating capacity of fatigued muscles. Conversely, joint viscosity was increased after fatigue potentially because of the reduced crossbridge detachment rate and prolonged relaxation associated with intracellular acidosis accompanying fatigue. Static stretch reflex gain decreased significantly at higher torque levels after fatigue, indicating that the isometric fatiguing exercise might be associated with a preferential change in properties of spindle chain fibers and bag2fibers. For matched pre- and postfatigue torque levels, dynamic reflexes contributed relatively more torque after fatigue, displaying higher dynamic reflex gains and larger dynamic electromyographic responses elicited by the controlled small-amplitude position perturbations. These changes appear to counteract the fatigue-induced reductions in joint stiffness and static reflex gain. The compensatory responses could be partly due to the effects of increasing the number of active motoneurons innervating the fatiguing muscles. This shift in operating point gave rise to significant compensation for the loss of contractile force. The compensation could also be due to fusimotor adjustment, which could make the dynamic reflex gain much less sensitive to fatigue than intrinsic stiffness. In short, the reduced contribution from intrinsic stiffness to joint torque was compensated by increased contribution from dynamic stretch reflexes after fatigue.
Multiple Sites of Action Potential Initiation Increase Neuronal Firing Rate
Authors: Baccus Stephen A. , Sahley Christie L. , Muller Kenneth J.
Published: December 2017

Sensory input to an individual interneuron or motoneuron typically evokes activity at a single site, the initial segment, so that firing rate reflects the balance of excitation and inhibition there. In a network of cells that are electrically coupled, a sensory input produced by appropriate, localized stimulation can cause impulses to be initiated in several places. An example in the leech is the chain of S cells, which are critical for sensitization of reflex responses to mechanosensory stimulation. S cells, one per segment, form an electrically coupled chain extending the entire length of the CNS. Each S cell receives input from mechanosensory neurons in that segment. Because impulses can arise in any S cell and can reliably propagate throughout the chain, all the S cells behave like a single neuron with multiple initiation sites. In the present experiments, well-defined stimuli applied to a small area of skin evoked mechanosensory action potentials that propagated centrally to several segments, producing S cell impulses in those segments. Following pressure to the skin, impulses arose first in the S cell of the same segment as the stimulus, followed by impulses in S cells in other segments. Often four or five separate initiation sites were observed. This timing of impulse initiation played an important role in increasing the frequency of firing. Impulses arising at different sites did not usually collide but added to the total firing rate of the chain. A computational model is presented to illustrate how mechanosensory neurons distribute the effects of a single sensory stimulus into spatially and temporally separated synaptic input. The model predicts that changes in impulse propagation in mechanosensory neurons can alter S cell frequency of firing by changing the number of initiation sites.
Excess Synchrony in Motor Cortical Neurons Provides Redundant Direction Information With That From Coarse Temporal Measures
Authors: Oram Mike W. , Hatsopoulos Nicholas G. , Richmond Barry J. , Donoghue John P.
Published: December 2017

Previous studies have shown that measures of fine temporal correlation, such as synchronous spikes, across responses of motor cortical neurons carries more directional information than that predicted from statistically independent neurons. It is also known, however, that the coarse temporal measures of responses, such as spike count, are not independent. We therefore examined whether the information carried by coincident firing was related to that of coarsely defined spike counts and their correlation. Synchronous spikes were counted in the responses from 94 pairs of simultaneously recorded neurons in primary motor cortex (MI) while monkeys performed arm movement tasks. Direct measurement of the movement-related information indicated that the coincident spikes (1- to 5-ms precision) carry ∼10% of the information carried by a code of the two spike counts. Inclusion of the numbers of synchronous spikes did not add information to that available from the spike counts and their coarse temporal correlation. To assess the significance of the numbers of coincident spikes, we extended the stochastic spike count matched (SCM) model to include correlations between spike counts of the individual neural responses and slow temporal dependencies within neural responses (∼30 Hz bandwidth). The extended SCM model underestimated the numbers of synchronous spikes. Therefore as with previous studies, we found that there were more synchronous spikes in the neural data than could be accounted for by this stochastic model. However, the SCM model accounts for most ( R 2 = 0.93 ± 0.05, mean ± SE) of the differences in the observed number of synchronous spikes to different directions of arm movement, indicating that synchronous spiking is directly related to spike counts and their broad correlation. Further, this model supports the information theoretic analysis that the synchronous spikes do not provide directional information beyond that available from the firing rates of the same pool of directionally tuned MI neurons. These results show that detection of precisely timed spike patterns above chance levels does not imply that those spike patterns carry information unavailable from coarser population codes but leaves open the possibility that excess synchrony carries other forms of information or serves other roles in cortical information processing not studied here.
Aging and Learning-Specific Changes in Single-Neuron Activity in CA1 Hippocampus During Rabbit Trace Eyeblink Conditioning
Authors: McEchron Matthew D. , Weible Aldis P. , Disterhoft John F.
Published: December 2017

Rabbit trace eyeblink conditioning is a hippocampus-dependent task in which the auditory conditioned stimulus (CS) is separated from the corneal airpuff unconditioned stimulus (US) by a 500-ms empty trace interval. Young rabbits are able to associate the CS and US and acquire trace eyeblink conditioned responses (CRs); however, a subset of aged rabbits show poor learning on this task. Several studies have shown that CA1-hippocampal activity is altered by aging; however, it is unknown how aging affects the interaction of CA1 single neurons within local ensembles during learning. The present study examined the extracellular activity of CA1 pyramidal neurons within local ensembles in aged (29–34 mo) and young (3–6 mo) rabbits during 10 daily sessions (80 trials/session) of trace eyeblink conditioning. A single surgically implanted nonmovable stereotrode was used to record ensembles ranging in size from 2 to 12 separated single neurons. A total of six young and four aged rabbits acquired significant levels of CRs, whereas five aged rabbits showed very few CRs similar to a group of five young pseudoconditioned rabbits. Pyramidal cells (2,159 total) were recorded from these four groups during training. Increases in CA1 pyramidal cell firing to the CS and US were diminished in the aged nonlearners. Local ensembles from all groups contained heterogeneous types of pyramidal cell responses. Some cells showed increases while others showed decreases in firing during the trace eyeblink trial. Hierarchical clustering was used to isolate seven different classes of single-neuron responses that showed unique firing patterns during the trace conditioning trial. The proportion of cells in each group was similar for six of seven response classes. Unlike the excitatory modeling patterns reported in previous studies, three of seven response types (67% of recorded cells) exhibited some type of inhibitory decrease to the CS, US, or both. The single-neuron response classes showed different patterns of learning-related activity across training. Several of the single-neuron types from the aged nonlearners showed unique alterations in response magnitude to the CS and US. Cross-correlation analyses suggest that specific single-neuron types provide more correlated single-neuron activity to the ensemble processing of information. However, aged nonlearners showed a significantly lower level of coincident pyramidal cell firing for all cell types within local ensembles in CA1.
Electrophysiology of Interneurons in the Glomerular Layer of the Rat Olfactory Bulb
Authors: McQuiston A. Rory , Katz Lawrence C.
Published: December 2017

In the mammalian olfactory bulb, glomeruli are surrounded by a heterogeneous population of interneurons called juxtaglomerular neurons. As they receive direct input from olfactory receptor neurons and connect with mitral cells, they are involved in the initial stages of olfactory information processing, but little is known about their detailed physiological properties. Using whole cell patch-clamp techniques, we recorded from juxtaglomerular neurons in rat olfactory bulb slices. Based on their response to depolarizing pulses, juxtaglomerular neurons could be divided into two physiological classes: bursting and standard firing. When depolarized, the standard firing neurons exhibited a range of responses: accommodating, nonaccommodating, irregular firing, and delayed to firing patterns of action potentials. Although the firing pattern was not rigorously predictive of a particular neuronal morphology, most short axon cells fired accommodating trains of action potentials, while most delayed to firing cells were external tufted cells. In contrast to the standard firing neurons, bursting neurons produced a calcium-channel-dependent low-threshold spike when depolarized either by current injection or by spontaneous or evoked postsynaptic potentials. Bursting neurons also could oscillate spontaneously. Most bursting cells were either periglomerular cells or external tufted cells. Based on their mode of firing and placement in the bulb circuit, these bursting cells are well situated to drive synchronous oscillations in the olfactory bulb.
Effects of Optic Flow in Motor Cortex and Area 7a
Authors: Merchant H. , Battaglia-Mayer A. , Georgopoulos A. P.
Published: December 2017

Moving visual stimuli were presented to behaving monkeys who fixated their eyes and did not move their arm. The stimuli consisted of random dots moving coherently in eight different kinds of motion (right, left, up, downward, expansion, contraction, clockwise, and counterclockwise) and were presented in 25 square patches on a liquid crystal display projection screen. Neuronal activity in the arm area of the motor cortex and area 7a was significantly influenced by the visual stimulation, as assessed using an ANOVA. The percentage of cells with a statistically significant effect of visual stimulation was 3 times greater in area 7a (370/587, 63%) than in motor cortex (148/693, 21.4%). With respect to stimulus properties, its location and kind of motion had differential effects on cell activity in the two areas. Specifically, the percentage of cells with a significant stimulus location effect was ∼2.5 times higher in area 7a (311/370, 84%) than in motor cortex (48/148, 32.4%), whereas the percentage of cells with a significant stimulus motion effect was ∼2 times higher in the motor cortex (79/148, 53.4%) than in area 7a (102/370, 27.6%). We also assessed the selectivity of responses to particular stimulus motions using a Poisson train analysis and determined the percentage of cells that showed activation in only one stimulus condition. This percentage was 2 times higher in the motor cortex (73.7%) than in area 7a (37.7%). Of all kinds of stimulus motion tested, responses to expanding optic flow were the strongest in both cortical areas. Finally, we compared the activation of motor cortical cells during visual stimulation to that observed during force exertion in a center→ out task. Of 514 cells analyzed for both the motor and visual tasks, 388 (75.5%) showed a significant relation to either or both tasks, as follows: 284/388 (73.2%) cells showed a significant relation only to the motor task, 27/388 (7%) cells showed a significant relation only to the visual task, whereas the remaining 77/388 (19.8%) cells showed significant relations to both tasks. Therefore a total of 361/514 (70.2%) cells were related to the motor task and 104/514 (20.2%) were related to the visual task. Finally, with respect to receptive fields (RFs), there was no clear visual receptive field structure in the motor cortical neuronal responses, in contrast to area 7a where RFs were present and could be modulated by the type of optic flow stimulus.
Medial Superior Olive of the Big Brown Bat: Neuronal Responses to Pure Tones, Amplitude Modulations, and Pulse Trains
Authors: Grothe Benedikt , Covey Ellen , Casseday John H.
Published: December 2017

The structure and function of the medial superior olive (MSO) is highly variable among mammals. In species with large heads and low-frequency hearing, MSO is adapted for processing interaural time differences. In some species with small heads and high-frequency hearing, the MSO is greatly reduced in size; in others, including those echolocating bats that have been examined, the MSO is large. Moreover, the MSO of bats appears to have undergone different functional specializations depending on the type of echolocation call used. The echolocation call of the mustached bat contains a prominent CF component, and its MSO is predominantly monaural; the free-tailed bat uses pure frequency-modulated calls, and its MSO is predominantly binaural. To further explore the relation of call structure to MSO properties, we recorded extracellularly from 97 single neurons in the MSO of the big brown bat, Eptesicus fuscus, a species whose echolocation call is intermediate between that of the mustached bat and the free-tailed bat. The best frequencies of MSO neurons in the big brown bat ranged from 11 to 79 kHz, spanning most of the audible range. Half of the neurons were monaural, excited by sound at the contralateral ear, while the other half showed evidence of binaural interactions, supporting the idea that the binaural characteristics of MSO neurons in the big brown bat are midway between those of the mustached bat and the free-tailed bat. Within the population of binaural neurons, the majority were excited by sound at the contralateral ear and inhibited by sound at the ipsilateral ear; only 21% were excited by sound at either ear. Discharge patterns were characterized as transient on (37%), primary-like (33%), or transient off (23%). When presented with sinusoidally amplitude modulated tones, most neurons had low-pass filter characteristics with cutoffs between 100 and 300 Hz modulation frequency. For comparison with the sinusoidally modulated sounds, we presented trains of tone pips in which the pulse duration and interstimulus interval were varied. The results of these experiments indicated that it is not the modulation frequency but rather the interstimulus interval that determines the low-pass filter characteristics of MSO neurons.
Spatial Processing in the Monkey Frontal Eye Field. II. Memory Responses
Authors: Umeno Marc M. , Goldberg Michael E.
Published: December 2017

Monkeys and humans can easily make accurate saccades to stimuli that appear and disappear before an intervening saccade to a different location. We used the flashed-stimulus task to study the memory processes that enable this behavior, and we found two different kinds of memory responses under these conditions. In the short-term spatial memory response, the monkey fixated, a stimulus appeared for 50 ms outside the neuron's receptive field, and from 200 to 1,000 ms later the monkey made a saccade that brought the receptive field onto the spatial location of the vanished stimulus. Twenty-eight of 48 visuomovement cells and 21/32 visual cells responded significantly under these circumstances even though they did not discharge when the monkey made the same saccade without the stimulus present or when the stimulus appeared and the monkey did not make a saccade that brought its spatial location into the receptive field. Response latencies ranged from 48 ms before the beginning of the saccade (predictive responses) to 272 ms after the beginning of the saccade. After the monkey made a series of 16 saccades that brought a stimulus into the receptive field, 21 neurons demonstrated a longer term, intertrial memory response: they discharged even on trials in which no stimulus appeared at all. This intertrial memory response was usually much weaker than the within-trial memory response, and it often lasted for over 20 trials. We suggest that the frontal eye field maintains a spatially accurate representation of the visual world that is not dependent on constant or continuous visual stimulation, and can last for several minutes.
Target Selection for Saccadic Eye Movements: Direction-Selective Visual Responses in the Superior Colliculus
Authors: Horwitz Gregory D. , Newsome William T.
Published: December 2017

We investigated the role of the superior colliculus (SC) in saccade target selection in rhesus monkeys who were trained to perform a direction-discrimination task. In this task, the monkey discriminated between opposed directions of visual motion and indicated its judgment by making a saccadic eye movement to one of two visual targets that were spatially aligned with the two possible directions of motion in the display. Thus the neural circuits that implement target selection in this task are likely to receive directionally selective visual inputs and be closely linked to the saccadic system. We therefore studied prelude neurons in the intermediate and deep layers of the SC that can discharge up to several seconds before an impending saccade, indicating a relatively high-level role in saccade planning. We used the direction-discrimination task to identify neurons whose prelude activity “predicted” the impending perceptual report several seconds before the animal actually executed the operant eye movement; these “choice predicting” cells comprised ∼30% of the neurons we encountered in the intermediate and deep layers of the SC. Surprisingly, about half of these prelude cells yielded direction-selective responses to our motion stimulus during a passive fixation task. In general, these neurons responded to motion stimuli in many locations around the visual field including the center of gaze where the visual discriminanda were positioned during the direction-discrimination task. Preferred directions generally pointed toward the location of the movement field of the SC neuron in accordance with the sensorimotor demands of the discrimination task. Control experiments indicate that the directional responses do not simply reflect covertly planned saccades. Our results indicate that a small population of SC prelude neurons exhibits properties appropriate for linking stimulus cues to saccade target selection in the context of a visual discrimination task.
Spatiotemporal Tuning of Directional Neurons in Mammalian and Avian Pretectum: A Comparison of Physiological Properties
Authors: Ibbotson Michael R. , Price Nicholas S. C.
Published: December 2017

Responses were recorded from 72 neurons in the wallaby's nucleus of the optic tract (NOT) during stimulation with drifting sinusoidal gratings at a range of temporal and spatial frequencies (TF and SF). Most cells (70/72) were TF tuned, but two were velocity tuned. The neurons are placed into two descriptive groups: fast and slow cells, which prefer SF/TFs of 0.06–0.6 cpd/0.4–20 Hz and 0.13–1 cpd/<1 Hz, respectively. The peak spatiotemporal tunings of the neurons are compared for motion in preferred and anti-preferred directions with little variation observed in most cases. The spatiotemporal properties of wallaby NOT are compared with those of pigeon lentiformis mesencephali: the avian homologue of NOT. The neurons in the pigeon and wallaby nuclei segregate into fast and slow cells that operate in similar spatiotemporal domains. The fast and slow cells segregate largely on the basis of TF in wallabies and SF in pigeons, but their respective velocity tuning properties are very similar. In both species, the mean velocity tuning for fast and slow cells is approximately 50°/s and 1°/s, respectively.
Alteration of Medullary Dorsal Horn Neuronal Activity Following Inferior Alveolar Nerve Transection in Rats
Authors: Iwata Koichi , Imai Takao , Tsuboi Yoshiyuki , Tashiro Akimasa , Ogawa Akiko , Morimoto Toshifumi , Masuda Yuji , Tachibana Yoshihisa , Hu James
Published: December 2017

The effects of inferior alveolar nerve (IAN) transection on escape behavior and MDH neuronal activity to noxious and nonnoxious stimulation of the face were precisely analyzed. Relative thresholds for escape from mechanical stimulation applied to the whisker pad area ipsilateral to the transection were significantly lower than that for the contralateral and sham-operated whisker pad until 28 days after the transection, then returned to the preoperative level at 40 days after transection. A total of 540 neurons were recorded from the medullary dorsal horn (MDH) of the nontreated naive rats [low-threshold mechanoreceptive (LTM), 27; wide dynamic range (WDR), 31; nociceptive specific (NS), 11] and sham-operated rats with skin incision (LTM, 34; WDR, 30; NS, 23) and from the ipsilateral (LTM, 82; WDR, 82; NS, 31) and contralateral MDH relative to the IAN transection (LTM, 77; WDR, 82; NS, 33). The electrophysiological properties of these neurons were precisely analyzed. Background activity of WDR neurons on the ipsilateral side relative to the transection was significantly increased at 2–14 days after the operation as compared with that of naive rats. Innocuous and noxious mechanical-evoked responses of LTM and WDR neurons were significantly enhanced at 2–14 days after IAN transection. The mean area of the receptive fields of WDR neurons was significantly larger on the ipsilateral MDH at 2–7 days after transection than that of naive rats. We could not observe any modulation of thermal responses of WDR and NS neurons following IAN transection. Also, no MDH neurons were significantly affected in the rats with sham operations. The present findings suggest that the increment of neuronal activity of WDR neurons in the MDH following IAN transection may play an important role in the development of the mechano-allodynia induced in the area adjacent to the area innervated by the injured nerve.
Dopamine D2 Receptor–Mediated Presynaptic Inhibition of Olfactory Nerve Terminals
Authors: Ennis Matthew , Zhou Fu-Ming , Ciombor Kelly J. , Aroniadou-Anderjaska Vassiliki , Hayar Abdallah , Borrelli Emiliana , Zimmer Lee A. , Margolis Frank , Shipley Michael T.
Published: December 2017

Olfactory receptor neurons of the nasal epithelium project via the olfactory nerve (ON) to the glomeruli of the main olfactory bulb, where they form glutamatergic synapses with the apical dendrites of mitral and tufted cells, the output cells of the olfactory bulb, and with juxtaglomerular interneurons. The glomerular layer contains one of the largest population of dopamine (DA) neurons in the brain, and DA in the olfactory bulb is found exclusively in juxtaglomerular neurons. D2 receptors, the predominant DA receptor subtype in the olfactory bulb, are found in the ON and glomerular layers, and are present on ON terminals. In the present study, field potential and single-unit recordings, as well as whole cell patch-clamp techniques, were used to investigate the role of DA and D2 receptors in glomerular synaptic processing in rat and mouse olfactory bulb slices. DA and D2 receptor agonists reduced ON-evoked synaptic responses in mitral/tufted and juxtaglomerular cells. Spontaneous and ON-evoked spiking of mitral cells was also reduced by DA and D2 agonists, and enhanced by D2 antagonists. DA did not produce measurable postsynaptic changes in juxtaglomerular cells, nor did it alter their responses to mitral/tufted cell inputs. DA also reduced 1) paired-pulse depression of ON-evoked synaptic responses in mitral/tufted and juxtaglomerular cells and 2) the amplitude and frequency of spontaneous, but not miniature, excitatory postsynaptic currents in juxtaglomerular cells. Taken together, these findings are consistent with the hypothesis that activation of D2 receptors presynaptically inhibits ON terminals. DA and D2 agonists had no effect in D2 receptor knockout mice, suggesting that D2 receptors are the only type of DA receptors that affect signal transmission from the ON to the rodent olfactory bulb.
Selective Cannabinoid CB1 Receptor Activation Inhibits Spinal Nociceptive Transmission In Vivo
Authors: Kelly Sara , Chapman Victoria
Published: December 2017

Cannabinoid1 (CB1) receptors are located at CNS sites, including the spinal cord, involved in somatosensory processing. Analgesia is one of the tetrad of behaviors associated with cannabinoid agonists. Here, effects of a potent cannabinoid CB1 receptor agonist arachidonyl-2-chloroethylamide (ACEA) on evoked responses of dorsal horn neurons in anesthetized rats were investigated. Extracellular recordings of convergent dorsal horn neurons were made in halothane anesthetized Sprague-Dawley rats ( n = 16). Effects of spinal application of ACEA on electrically evoked responses of dorsal horn neurons were studied. Mean maximal effects of 0.5, 5, 50, and 500 ng/50 μl ACEA on the C-fiber-mediated postdischarge response were 79 ± 6, 62 ± 10, and 54 ± 7% ( P < 0.01), 45 ± 6% ( P < 0.01), of control, respectively. ACEA (500 ng/50 μl) also reduced the C-fiber-evoked nonpotentiated responses of neurons (59 ± 9% of control, P < 0.05) and Aδ-fiber-evoked responses of neurons (68 ± 10% of control, P < 0.01). Minor effects of ACEA on Aβ-fiber-evoked responses were observed. Spinal pre-administration of the selective CB1 receptor antagonist SR141716A (0.01 μg/50 μl) significantly reduced effects of ACEA (500 ng/50 μl) on postdischarge responses of dorsal horn neurons. This study demonstrates that spinal CB1 receptors modulate the transmission of C- and Aδ-fiber-evoked responses in anesthetized rats; this may reflect pre- and/or postsynaptic effects of cannabinoids on nociceptive transmission. CB1 receptors inhibit synaptic release of glutamate in rat dorsolateral striatum, a similar mechanism of action may underlie the effects of ACEA on noxious evoked responses of spinal neurons reported here.