bluuebunny/crossref_metadata_2025 huggingface dataset:
Degree of interocular synchrony required for maintenance of binocularity in kitten's visual cortex
Authors: Blasdel G. G. , Pettigrew J. D.
Published: December 2017

1. The importance of synchronous activation in maintaining cortical binocularity was studied physiologically in kittens that had been reared under different regimens of alternating monocular deprivation. 2. Three different techniques were employed to provide alternate monocular stimulation: a) mechanical shutters placed before the animals' eyes; b) goggles fitted with complementary colored cutoff filters, which restricted visual input to one eye at a time; and c) two rotating gratings that were 90 degrees out of phase. In the third technique, the gratings were always orthogonal to one another and viewed separately through cutoff filters. This allowed us to exploit the orientation selectivity of cortical cells and thereby stimulate them alternately through each eye without simultaneously affecting activity in the dorsal lateral geniculate nucleus (dLGN). 3. We based our conclusions on a sample of 691 neurons, which we recorded in 21 animals. Results with all techniques were remarkably consistent. Binocular cortical inputs predominated at normal or nearly normal levels, even when a number of seconds elapsed between successive exposures of each eye. 4. An interonset interval of at least 10 s was required to make a substantial reduction in binocularity. This interval can be separated into two parts--the duration of exclusive monocular stimulation and the time when neither channel receives input. Of these, the latter appeared to be less important. Blanking times of 0.15--1.0 s did not affect binocularity if the interonset interval was 1 or 10 s; and in one experiment where the blanking time was 9 s, the resulting disruption in binocularity was less than that found with shorter blanking times and the same interonset interval. 5. Our results imply that mechanisms responsible for the disappearance of binocular cortical inputs require independent stimulation of each eye for periods of at least a few seconds; this stimulation must be of a kind that is known to excite cortical cells. Our results with the rotating grafting show, in addition, that the mechanisms whose timing we have measured are intrinsic to the cortex.
Responses of vibrissa-sensitive cortical neurons in normal and prenatally X-irradiated rat
Authors: Ito M. , Kawabata M. , Shoji R.
Published: December 2017

1. Rats were irradiated by 200 R of X ray on day 17 (the 18th day) of gestation through the body wall of the mother. When they underwent the following electrophysiological tests at the age of 3-4 mo, the somatosensory cortex showed a lack of layers II, III, IV, and Va, as described by previous investigators (3, 4). 2. Spike responses to quick whisker deflections were recorded from single cells in the somatosenory cortex of normal and prenatally X-irradiated rats. 3. In normal animals, single units often responded to several whiskers, but the magnitudes (response latency and firing probability) of the responses were graded around a whisker in the "center" of the field that gave rise to the strongest response. During electrode penetration perpendicular to the cortical surface, such a center remained unchanged or shifted to another whisker that was immediately adjacent. As for the large-sized, initially positive unitary spikes (typically 2 mV or higher) sampled in this study, no systematic change in the response latency, the size of receptive field, or response probability was detected during the penetration. 4. The above description holds also for the irradiated rats except that the response latency was prolonged when compared to the normal controls. 5. Cortical laminar analysis of field potentials revealed that while the earliest electric sink appeared in layer IV in the controls, that in the irradiated rats was observed in layer Vb. However, there was no difference in the latency of these potentials between the two groups, suggesting that vibrissal sensory signals reach the cortical level normally even in the irradiated rats. The prolonged latency of the irradiated cortical neuronal response could thus be ascribed to an abnormal intracortical delay, which was most likely associated with the failure of development of layer IV stellate cells in these preparations. 6. A possibility as to how the layer IV stellate cells are involved in input-output relationships in the normal somatosensory cortex is presented and discussed.
Recovery of function in dorsal horn following partial deafferentation
Authors: Pubols L. M. , Goldberger M. E.
Published: December 2017

1. Collateral sprouting of L6 dorsal root afferents within the dorsal horn of the L6 spinal cord segment has been shown anatomically to occur following transection of all other lumbosacral dorsal roots in the cat. The present study was performed to examine a possible physiological correlate of that sprouting, namely, an altered somatotopic organization of the dorsal horn at L6. This was evaluated by microelectrode mapping of the L6 dorsal horn in normal cats and in cats with L6 spared, lumbosacral dorsal rhizotomies performed 2 days (subacute spared root) or more than 8 wk (chronic spared root), prior to recording. 2. In normal cats the mediolateral somatotopic sequence of hindlimb representation in the L6 dorsal horn is ventral digits 2 and 3, dorsal digits 2 and 3, dorsal foot, rostral and lateral ankle, lateral leg, lateral thigh, and back. In both subacute and chronic spared-root cats the somatotopic sequence is similar to that of normal cats, but there is a loss of proximal thigh and back representation. This proximal body region is represented at the lateral edge of the dorsal horn in normal animals. 3. There was a partial loss of responsiveness of cells in the dorsal horn in the subacute spared-root group and a partial recovery of responsiveness in the chronic group. In the subacute group punctures exhibiting no responses to tactile input tended to be clustered in the lateral dorsal horn. 4. The lateral one-fourth of the dorsal horn in each animal was analyzed in terms of the percentage of recording loci occurring within it. The percentages of recording loci having receptive fields proximal to, distal to, and spanning the middle of the thigh (proximal, distal, and intermediate RFs) were tabulated for each animal. Subacute animals had a significantly lower-than-normal overall percentage of responsive loci in the lateral dorsal horn, but chronic animals did not. The percentage of distal fields therein was not different for the normal versus the subacute group, signifying that the loss of proximal and intermediate fields was responsible for the difference in overall percentage. Chronic animals, however, had significantly more distal fields than did normals. When all fields having any distal component were compared (i.e., distal and intermediate), the difference between the chronic and normal groups did not reach significance. One possible explanation of these findings is that loci having both proximal and distal RF components are unresponsive 2 days after partial denervation, but recover responsiveness to their spared distal input over an 8-wk period. One possible mechanism mediating these changes is localized sprouting of intact, spared axons. Other mechanisms of functional recovery, such as interneuronal sprouting, denervation supersensitivity, and unmasking of latent synapses, are discussed in relation to these and other data.
Eye movements evoked by microstimulation of dorsal cap of inferior olive in the rabbit
Authors: Barmack N. H. , Hess D. T.
Published: December 2017

1. Microstimulation was used in an attempt to activate selectively neurons of the dorsal cap of the inferior olive in unanesthetized rabbits, and the eye movements evoked by this microstimulation were recorded. 2. Trains of microstimulation (20--50 microA, 0.1- to 0.2-ms pulses, 10--60 pulses/s, 2--8 s duration) evoked low-velocity conjugate eye movements directed toward the side of the stimulated olive. These evoked eye movements were interrupted by resetting eye movements in the opposite direction and could be evoked only if the rabbit was in darkness. 3. The velocity of the evoked eye movements increased during a stimulus train and gradually decreased after the stimulation was terminated. 4. The low-velocity eye movements appeared to combine with eye movements evoked by vestibular stimulation without any significant interaction. 5. After transection of the olivocerebellar pathway or destruction of the contralateral cerebellar flocculus, dorsal cap microstimulation no longer evoked ipsilaterally directed eye movements.
Response to sudden torques about ankle in man. II. Postmyotatic reactions
Authors: Gottlieb G. L. , Agarwal G. C.
Published: December 2017

1. Torques were applied to dorsiflex or plantarflex the ankle joint of normal human subjects who were instructed to react to them in various ways. Myoelectric and mechanical responses were recorded and analyzed. 2. Myoelectric responses in triceps surae or tibialis anterior with times of onset between 100 and 200 ms are conditional on the instruction to the subject and not the direction of the applied torque. These responses are termed postmyotatic responses. 3. The latency of the postmyotatic response is the same in both triceps surae and tibialis anterior. It is not dependent on the direction of the applied torque and consequently is not a "stretch reflex," but a triggered reaction. 4. When the subject is sitting relaxed and instructed to resist the applied torque, the magnitude of the postmyotatic response is highly and linearly correlated with the rate of ankle rotation produced by the disturbing torque. 5. Tonic contraction of the muscles prior to the onset of a stretching torque has only a slight effect on the magnitude of the postmyotatic response and usually reduces it. Prior tonic contraction of the antagonist also has a modest effect in reducing the response. 6. Instructing the subject to resist a torque as quickly and strongly as possible increases the magnitude of the postmyotatic response but has little effect on its linear functional relationship to the magnitude of the mechanical stimulus. 7. The postmyotatic response, although voluntary and kinesthetically triggered, is not completely equivalent to a visually triggered voluntary reaction because under experimental situations designed to measure simple reaction times and choice reaction times of the postmyotatic response, no significant difference is found between the two conditions. 8. It is suggested that the peripheral afferent pathways of the stretch reflex play a dual role in determining postmyotatic responses. First, they provide to supraspinal centers one early proprioceptive signal about limb perturbation that can trigger a previously selected mode of response. Second, they modulate that response by convergence, at the segmental level, of peripheral afferent signals with the descending command signals.
An intracellular investigation of cat vesical pelvic ganglia
Authors: Griffith W. H. , Gallagher J. P. , Shinnick-Gallagher P.
Published: December 2017

1. Intracellular recording techniques were used to study individual neurons in the cat parasympathetic vesical pelvic ganglion (VPG). 2. Active and passive electrical properties were determined from 140 ganglion cells (35 preparations). 3. Three types of ganglion cells were distinguished. Type I (A and B) cells were nonaccommodating cells in response to depolarizing current pulses. Type II cells showed accommodation to depolarizing current pulses. Other cells, presumably glia, were also impaled. 4. Type IB cells exhibited two kinds of nonsynaptic spontaneous activity, spontaneous action potentials (60-70 mV) and small spontaneous potentials (up to 5 mV). Characteristics of the spontaneous activity were examined. 5. The duration of the spikes' afterhyperpolarization resulting from either orthodromic or antidromic train stimulation was dependent on the frequency of train stimulation. No long-lasting posttrain hyperpolarization was observed. 6. Chlorisondamine (10(-6) M), d-tubocurarine (10(-5) M), and hexamethonium (10(-5) M) reversibly blocked orthodromic responses. 7. The VPG is a useful model to study parasympathetic ganglionic transmission at the cellular level.
Mechanisms responsible for changes observed in response properties of partially deafferented insect interneurons
Authors: Murphey R. K. , Levine R. B.
Published: December 2017

1. Two pairs of large sensory interneurons, the medial and lateral giant interneurons (MGI and LGI), in the abdominal nervous system of crickets were examined after being partially deafferented throughout postembryonic development. Each of these interneurons receives a synaptic input from sensory neurons in a pair of appendages called cerci. The experiment consisted of removing one of these appendages at hatching and examining the morphological and physiological consequences for the MGI and LGI. 2. The morphological consequences of deafferentation were examined by injecting neurons with cobalt acetate and intensifying the profiles either in section or whole mount with a modified Timm's method. We confirmed previous reports that the main dendritic branches were shorter than controls when deafferented. In addition, we demonstrated that the many spinelike processes projecting from the main dendrites were shorter than in controls. The density of spines per unit length of main dendrite was approximately the same on control and treated dendrites. Neither the MGI nor the LGI sprouted new dendrites into normally afferented areas as a result of partial deafferentation. Short periods of deafferentation late in development had similar though less drastic effects on the structure of MGI. 3. The MGI was found to receive stronger than normal excitatory input from the remaining cercus when one cercus was absent throughout postembryonic development. An examination of remaining inhibitory inputs to both the MGI and the LGI demonstrated that these pathways were weaker than normal. The results suggest that the increase in excitability observed in MGI when partially deafferented for long periods is due to removal of inhibition rather than direct changes in the strength of excitatory inputs.
Rapid ankle extension during paw shakes: selective recruitment of fast ankle extensors
Authors: Smith J. L. , Betts B. , Edgerton V. R. , Zernicke R. F.
Published: December 2017

1. Electromyographic (EMG) signals from slow (soleus) and fast (lateral gastrocnemius) ankle extensors of six cats were recorded during rapid and alternate flexion-extension of the hindlimb elicited by placing the paw in water or by sticking tape to the plantar pads. High-speed 16-mm film, taken at 100 or 200 frames/s, was analyzed to determine the knee and ankle joint kinematics. 2. During 77 typical records, which averaged eight paw shakes each, a single extension-flexion cycle measured by the paw shake interval (PSI) of the electromyogram record, averaged 88 ms and ranged from 55 to 110 ms. LG EMG bursts of 10 ms in duration were synchronized with the peak displacement of ankle flexion. The SOL was inactive throughout these typical records. 3. During four atypical records from one cat, the average OSI was 141 ms, and both lateral gastrocnemius (LG and soleus (SOL) were active simultaneously. At a range of 6--8 cycles/s, these slower shakes are comparable to rhythmic actions of scratching )12) and locomotion (27); cyclic movements that typically include the recruitment of soleus. 4. It is suggested that paw shaking is an automatic movement triggered primarily by large, low-threshold afferents innervating the central plantar pads, which may selectively recruit the fast extensors while inhibiting the slow extensor. This is the only movement of the hindlimb recorded to date in our laboratory in which the tlg was active without the SOL. This unique dissociation of recruitment of slow and fast ankle extensors may be dictated by the time constraints imposed by the rapid cyclic movements of paw shaking.
Distributed processing by visual interneurons of crayfish brain. I. Response characteristics and synaptic interactions
Authors: Wood H. L. , Glantz R. M.
Published: December 2017

1. The visual responses and synaptic interactions of a small population of crayfish interneurons are described. 2. The discharge of optic nerve sustaining fibers (tonic on-cells) appears in the brain prior to the onset of the light-evoked discharge of any of the higher order, descending visual interneurons. Direct depolarization of impaled sustaining fibers elicits impulse responses in a large number of descending interneurons. These results indicate that the sustaining fibers provide the visual input to higher order interneurons. 3. Four classes of descending interneurons can be distinguished. All arise in the brain and have axons in the circumesophageal connectives. The response forms vary from tonic to phasic. Two classes of tonic cells are distinguished by response latency and two classes of phasic neurons are distinguished by the rate of response adaptation. The phasic neurons exhibit the most rapid habituation, the largest receptive fields, and the most potent nonvisual inputs. 4. Synaptic interactions are studied by cross-correlation of impulse trains and direct observation of synaptic potentials. About 84% of the cells examined reveal evidence of functional connections to other descending visual interneurons. 5. Cross-correlograms derived from impulses of parallel interneurons exhibit a mean time lage to peak of 6.6 +/- 2.8 ms (SD). The measured delay from EPSP onset to spike onset is 6.0 +/- 4.0 ms. Thus a substantial proportion of the correlogram's time lag to peak is associated with postsynaptic integration time. 6. Direct depolarization of impaled tonic on-cells elicits impulse activity at a fixed delay in other descending interneurons. 7. Synaptic potentials in descending visual interneurons are correlated 1:1 with axon spikes of other descending interneurons. 8. A third of the 80 interactions examined were reciprocal and many cells were implicated in multiple interactions. 9. The results suggest that the descending visual interneurons are organized in a complex network, which can cordinate the discharge of various subpopulations of the ensemble. It is proposed that the coordination of impulses in parallel interneurons may be a mechanism for coding and information transfer in the crayfish nervous system.
Distributed processing by visual interneurons of crayfish brain. II. Network organization and stimulus modulation of synaptic efficacy
Authors: Wood H. L. , Glantz R. M.
Published: December 2017

1. Multiple interactions were examined between five or six visual neurons simultaneously monitored in the circumesophageal connective. 2. A single neuron can make divergent connections to at least five other visual interneurons. 3. Conversely, a single cell may receive convergent inputs from up to four visual interneurons. 4. The convergent interactions are sufficiently intense so that 80--90% of a postsynaptic cell's visual activity can be attributed to observed network interactions. 5. Connectivity diagrams suggest that the descending interneurons, which arise in the visual neuropil of the brain, are organized into three interconnected layers: a) neurons that receive input from the optic nerve and project to other visual interneurons, b) neurons that both receive input and project to other descending interneurons in the brain--these cells exhibit a preponderance of reciprocal interactions, c) neurons that receive input from both the first and second network layers and project exclusively to the more caudal ganglia of the ventral nerve cord. 6. The network is systematically organized with respect to visual and nonvisual responsiveness. The cells of the first layer exhibit the strongest visual responses. The cells of the third layer exhibit spontaneous activity and the strongest tactile and/or proprioceptive responses. 7. The intensity of the network interactions is under stimulus control. The synaptic efficacy of a presynaptic spike can vary by over 100-fold as a consequence of stimulus presentation and/or location. The expressed organization of the network thus exhibits a dynamic, stimulus-dependent, plasticity. 8. The results indicate that the descending visual interneurons of the brain rather than forming a parallel tract actually constitute a complex distributed network. Furthermore, the results indicate the feasibility of population neural coding based on stimulus-dependent inpulse coordination in an array of neurons.
Spatial organization of catfish retinal neurons. I. Single- and random-bar stimulation
Authors: Davis G. W. , Naka K.
Published: December 2017

1. Receptive-field profiles of catfish (Ictalurus punctatus) retinal neurons were produced by a moving single bar or a moving random grating, which was swept across the cell's receptive field at a constant speed. 2. Bipolar cells form either an on- or an off-center biphasic field and are approximately linear in time and space. 3. Type-C or transient cells form predominantly monotonic receptive fields. We find two subclasses, one slow and the other fast transient cells. They can be identified functionally as well as morphologically. 4. Type-N or sustained cells form a biphasic receptive field, which is revealed by a bar of light. The monotonic field found by a spot or an annulus of light represents activity of the cell's field center. 5. There are two ganglion-cell types, small-field cells and large-field cells. It appears as if small-field cells copy signals in the bipolar cells and large-field cells, signals in the type-N cells. We suggest, however, that this observation represents the limitation imposed by our stimuli rather than an overall functional characteristic of catfish ganglion cells.
Inhibition of mechanosensory interneurons in the crayfish. I. Presynaptic inhibition from giant fibers
Authors: Kennedy D. , McVittie J. , Calabrese R. , Fricke R. A. , Craelius W. , Chiapella P.
Published: December 2017

1. Sucrose-gap and intracellular recordings were used to study the primary afferent depolarization (PAD) produced in mechanosensory afferents by impulses in lateral and medial giant axons, which are the command cells for the tail flip escape response in the crayfish. 2. The lateral and medial giant axons produce PAD through a polysynaptic interneuronal pathway. The response has a relatively long intraganglionic latency (7--11 ms), and command-evoked PAD can be recorded in ganglia from which the giant axons have been experimentally disconnected. 3. The final neurons of the pathway that delivers inhibition are few in number and extensive in distribution; most appear to be common to lateral and medial giant pathways. 4. At least some of the inhibitory interneurons have axons in the interganglionic connectives and probably produce both presynaptic and postsynaptic inhibition. 5. Stimulation of the lateral, but not the medial, giant axons causes a small, short-latency deplorization that is stable at high repetition rates. This small potential can be accounted for by transmission across known electrical synapses between mechanosensory afferents and the lateral giants in each abdominal ganglion. 6. Repetitive stimulation of the lateral giant axons causes substantial augmentation of PAD, apparently through recruitment of additional interneurons. PAD evoked by a single medial giant (MG) stimulus is generally much larger than that elicited by a single lateral giant (LG) spike. However, MG-PAD summates little and so the maximum PAD deltaV reached during repetitive firing is equivalent for the two types of giant axons. 7. Iontophoresis of gamma-aminobutyric acid (GABA) into the ganglionic neuropil depolarizes the primary afferents and blocks activity in neurons that have axons in the interganglionic connective. 8. The extrapolated PAD reversal potential and pharmacological studies suggest that a GABA-mediated chloride conductance increase is involved in the production of PAD.
Extrageniculostriate vision in the monkey. VII. Contrast sensitivity functions
Authors: Miller M. , Pasik P. , Pasik T.
Published: December 2017

1. Psychophysical and electrophysiological experiments have indicated the importance of spatial frequency components and their respective contrasts and orientations for the recognition of patterns. It is in the striate cortex where these types of information first converge, a fact that lends support to the accepted crucial role of this structure in pattern discrimination. 2. Monkeys with total bilateral ablation of the striate cortex, however, retain a residual capacity for pattern discrimination and also can differentiate between a vertical and an oblique luminous bar. The present study explores their capacity for spatial frequency detection both as a function of contrast and, by extrapolation, at maximum contrast (visual acuity measure). 3. Monkeys were presented with a forced choice between a homogeneous target and a vertically oriented sinusoidal grating in a pulling-in apparatus. Stimuli were produced by the transillumination of transparencies at spatial frequencies of 0.5, 1.0, 2.0, 4.0, 8.0, 16, and 32 cycles/deg, in 0.1-log unit steps of contrast from 0.79 to 0.006. The stimuli subtended 8 degrees of visual angle and were matched for mean luminance at 20 cd/m2. After mastering the discrimination of one spatial frequency at the highest contrast, contrast thresholds were first estimated by a staircase technique, and then determined by the method of constant stimuli. The procedure was repeated for each spatial frequency before and after histologically verified total bilateral removal of striate cortex and partial damage to circumstriate cortices. 4. Discrimination at all spatial frequencies was mastered by all normal monkeys. Postoperatively, they could solve only problems with frequencies between 0.5 and 4.0 cycles/deg. 5. Contrast sensitivity (threshold-1) functions for normal and destriated monkeys have the characteristic inverted J shape. The high- and low-frequency limbs are related exponentially to spatial frequency, and the peak of the curve is about 2.0 cycles/deg. The dimensions of the functions, however, change significantly following the ablation. Sensitivity is depressed at all spatial frequencies. The mean “visuogram” indicates a 26-dB flat loss. 6. The mean high-frequency cutoff point is 43 cycle/deg preoperatively and 12 cycles/deg postoperatively, equivalent to 0.7' and 2.5' of arc, respectively. The latter value is not worse than 20/80 on the Snellen chart. 7. The variability of the response at each spatial frequency in the staircase method and the slope of the psychometric function derived from the method of constant stimuli provide a measure of “instability” and “precision,” respectively, which are inversely related. Preoperatively, precision is significantly greater at high than at low spatial frequencies. Postoperatively, it is similar at all frequencies, and the values are lower than those determined preoperatively. 8. The results demonstrate that destriated monkeys can detect gratings, although to a lesser degree than normal animals…
Inhibition and excitation of primate spinothalamic tract neurons by stimulation in region of nucleus reticularis gigantocellularis
Authors: Haber L. H. , Martin R. F. , Chung J. M. , Willis W. D.
Published: December 2017

1. Electrical stimulation in the region of the nucleus reticularis gigantocellularis (NGc) in anesthetized monkeys inhibited or excited spinothalamic tract neurons in the lumbosacral and cervical enlargements. 2. The descending effects were generally more pronounced for activity evoked by cutaneous A-delta-fibers than for activity produced by large myelinated cutaneous afferents. Nevertheless, the responses to all types of natural stimuli used could be inhibited or facilitated. 3. The excitation from repeated brief stimulus trains to the NGc sometimes increased progressively, suggesting the existence of a positive feedback system. Occasionally, repeated stimulation of the NGc produced a progressively greater inhibition. 4. The threshold stimulus strength to elicit the inhibitory and excitatory actions was usually less than 50 microA, and in some cases less than 25 microA. The inhibition and excitation increased as the stimulus intensity was raised above the threshold value, or as the number and/or frequency of pulses in the stimulus train was increased. 5. The strongest inhibition and excitation was produced by stimulation within the NGc on either side of the brain stem. There was no obvious topographic organization of inhibitory and excitatory zones. 6. Dorsolateral tractotomies in the high cervical spinal cord did not prevent the effects of NGc stimulation, indicating that the inhibitory and excitatory pathways descend in the ventral parts of the white matter. 7. It is suggested that the inhibition and excitation are mediated by the medullary reticulospinal system.
Physiological basis of feeding behavior in Tritonia diomedea. II. Neuronal mechanisms
Authors: Willows A. O.
Published: December 2017

1. The nudibranch mollusk Tritonia diomedea feeds by biting and drawing pieces of coelenterate sea whips into its buccal cavity. It then swallows them in a series of cyclic ingestion movements. The coordinated pattern of swallowing can be elicited in reduced preparations by stimulation of identifiable neurons in cerebral or buccal ganglia. 2. Swallowing normally proceeds as a cyclic pattern of protraction and retraction movements driven by alternating bursts in odontophore-radula protractor and retractor motor neurons (MNs), with simultaneous coordination of many other major neurons. 3. Brief or prolonged constant-current stimulation of certain individual buccal ganglion (SW) premotor neurons reliably triggers one or more complete cycles of impulse bursts in motor neurons with coordinated movements of the jaws and buccal mass. The MN bursts produced in this way resemble the ones seen during feeding. Some SW neurons trigger responses that greatly exceed the duration of the stimulus; others drive cyclic output in the motor system whose duration corresponds closely to the duration of the depolarizing current. As well, the rate of MN bursting can be modulated by steady currents of different amplitudes injected into these SW neurons. There are, however, alternative sensory and motor routes independent of SW neurons by which the motor pattern may be elicited and modulated. 4. A search for the source of the feeding rhythm resulted in the identification of a pair of motor neurons (B5) that have prominent burst and pattern-generating capabilities independent of SW activation. They fire vigorous impulse bursts on rebound from spontaneously occurring IPSP waves or from imposed hyperpolarizing potentials of similar amplitude and duration. 5. Constant prolonged depolarizing currents injected into B5 result in the production of repetitive bursts in other MNs that resemble in amplitude and time course those seen during feeding. Cyclic bursting generated in this way apparently entrains other parts of the feeding motor generator since a coordinated output of appropriately phased hyperpolarizing waves, antagonistic EPSP volleys, motor bursts, and movements is simultaneously recorded in other, unstimulated motor neurons of the system. However, the SW neurons are not always entrained by such MN-generated bursting. 6. Brief stimulation of B5 (sufficient to elicit one or a few impulses) also results in the appearance of a depolarizing afterpotential, which is itself capable of regenerating further impulses. When prolonged, constant currents are applied, the impulses that result form bursts whose durations and interburst intervals depend on the amplitude of the stimulating currents. The spike and burst-generating qualities of these neurons (which may include endogenous and interactive components) are sufficient to serve as a source of timing and phasing for the motor pattern.
Deficits in eye movements following frontal eye-field and superior colliculus ablations
Authors: Schiller P. H. , True S. D. , Conway J. L.
Published: December 2017

1. This study investigated the effects of frontal eye-field and superior colliculus ablations on fixation patterns and saccadic eye movements. Monkeys were trained to pick apple pieces out of a multiple-slotted apple board while their heads were fixed. Eye movement records were obtained using predominantly the implanted search-coil method. 2. Both unilateral and bilateral frontal eye-field lesions produced only temporary deficits in eye movements. Following surgery monkeys tended to neglect the contralateral peripheral visual field and made fewer saccades to peripheral targets. Recovery was virtually completed in 2-4 wk. 3. Superior colliculus ablation reduced fixation accuracy, saccade frequency, and saccade velocity. These deficits showed little recovery with time. 4. Paired frontal eye-field and superior colliculus lesions produced dramatic deficits in visually triggered eye movements. Animals could no longer fixate their eyes on visual targets with any degree of accuracy. The range of eye movements was greatly reduced, as was the frequency and velocity of saccades. These deficits showed little recovery with time. 5. These results suggest that visually triggered saccadic eye movements are controlled by two parallel channels, one involving the superior colliculus and the other the frontal eye field.
Neurogenesis in olfactory epithelium: loss and recovery of transepithelial voltage transients following olfactory nerve section
Authors: Simmons P. A. , Getchell T. V.
Published: December 2017

1. Unilateral olfactory nerve section was performed on the salamander, Ambystoma tigrinum. Physiological recordings and macroscopic observations were made to investigate the physiological correlates of functional recovery in the olfactory epithelium. 2. Slow transepithelial voltage transients, Veog, evoked by several odorous stimuli systematically decreased in amplitude during the initial 7 days and were not recorded at 10 days following nerve section, suggesting retrograde degeneration of receptor neurons. This was true for negative Veog(-), and positive, Veog(+), response components. Responses obtained from the untreated contralateral side of each animal remained similar to nonaxotomized controls. 3. Progressive recovery of the voltage transients was studied at 24, 45, 80, and 100 days following nerve section. At all stages of recovery, the wave form and time course of the responses were characteristic for each stimulus. This suggested that the response properties of the newly differentiated neuronal population were similar to those of the mature population. 4. At 100 days, response amplitudes evoked by all stimuli were similar to control values at all recording sites on the epithelial surface. The simultaneous loss and recovery of positive and negative components of the Veog indicated that the sources of both are dependent on the presence of functionally mature olfactory receptor neurons. 5. Visual inspection indicated that the olfactory nerve was reconstituted and reconnected to the olfactory bulb between 30-60 days following transection. The fact that physiological activity was recorded in the epithelium prior to this event suggests that molecular recognition and sensory transduction are not dependent on connectivity with the olfactory bulb. 6. It is concluded that physiological recovery of the olfactory receptor cell population occurs following axotomy. The time course of recovery was consistent with morphological evidence (see Ref. 57), indicating that newly differentiated receptor neurons are derived from cells in the basal region of the epithelium and replace the population lost through retrograde degeneration.
Component of muscle spindle discharge related to arterial pulse
Authors: McKeon B. , Burke D.
Published: December 2017

1. In human subjects microelectrode recordings were made from 25 muscle spindle afferents from the pretibial muscles. 2. The spike discharges of three endings were locked in time to the arterial pulse. With 17 of the remaining endings, there was a significant pulse-related modulation of discharge rate. For these 20 endings the latency to the onset of the pulse-related influence was 200-310 ms. 3. The time course of the modulation of discharge rate was similar to that of arterial blood flow, as estimated using a Doppler flowmeter. With four endings occlusion of blood flow using a sphygmomanometer cuff reduced any modulation. 4. For five endings the contribution by the arterial modulation to the variance of discharge of the ending was 3-54%. For the population of endings there was no significant relationship between the depth of modulation and coefficient of variation. 5. It is concluded that the arterial pulse can be significant contributor to the variability of muscle spindle discharge. The pulsatile effects seen in the responses of single afferents are unlikely to be eliminated in the summed activity forming the population response. This could constitute a limitation of the information capacity of the population of muscle spindle afferents.
Brief periods of monocular deprivation in kittens: effects of delay prior to physiological study
Authors: Freeman R. D. , Olson C.
Published: December 2017

1. Brief periods of selective visual exposure in 4-wk postnatal kittens can cause pronounced alterations in striate cortex. The processes underlying these changes may be similar to those of other short-term neural events such as memory or learning, and attempts have been made to link these areas. In particular, it has been reported that the effects of selective visual exposures are consolidated if a delay is interposed between rearing and physiological study. 2. We have tested this notion directly. Normally reared kittens were monocularly occluded for 8 or 24 h on postnatal day 29. Half of the 8-h and of the 24-h groups were tested physiologically immediately following monocular exposure, while the other halves were recorded after an intervening session of 8 or 48 h, respectively, during which the kittens were kept in darkness. 3. Extracellular responses of cortical neurons were analyzed, and primary attention was paid to absolute and relative interocular response strengths of each cell. Ocular dominance distributions from all kittens were significantly abnormal, but invariably, effects were less extensive for those who had experienced a period of dark rearing prior to physiological study. 4. These results are clearly at odds with the idea that the effects of monocular deprivation were consolidated by allowing a period of delay between exposure and physiological recording. On the contrary, during the time the kittens spent in darkness, it appears that some functional recovery of binocular pathways occurred. 5. To explore the minimal period of monocular occlusion that could cause cortical disruption, we studied an additional group of normally reared kittens that were occluded for only 4 h on postnatal day 29. Effects for this group were small but ocular dominance patterns were significantly abnormal. 6. An alternative procedure was used for the delay period between 24-h monocular occlusion and physiological study. Prior to recording, these kittens spent 48 h in a normally illuminated colony. Ocular dominance histograms were normal, indicating that complete recovery had occurred from the initial monocular deprivation. 7. Histological reconstructions were made to estimate effects in different cortical laminae, but conclusions must be tentative because of small samples. In the group that had been monocularly occluded for 4 h and then recorded, inactivation of binocular pathways was most apparent in layers IV and V. This results suggest that the process deprivation disconnection during monocular deprivation occurs frist in these layers. Findings from the groups in which a delay was imposed between monocular exposure and recording indicate that functional binocular recovery occurs frist in layer IV and above and last in layer VI.
Motor-unit activation patterns in lengthening and isometric contractions of hindlimb extensor muscles in the decerebrate cat
Authors: Cordo P. J. , Rymer W. Z.
Published: December 2017

1. Multiunit integrated electromyographic (EMG) signals and single-unit EMG potentials were recorded during isometric and lengthening (stretch reflex) contractions of soleus and medial gastrocnemius (MG) muscles in 20 decerebrate cats. Patterns of motor-unit recruitment and rate modulation were examined in isometric muscles and during constant-velocity stretches. 2. Analysis of multiunit EMG activity and its relationship to active force revealed a marked difference between isometric and lengthening contractions. While the force-EMG relationship for isometric contractions was characteristically linear, the relation recorded during stretch-reflex responses showed a disproportionate early EMG increase, which was most obvious at low force levels, suggesting that the efficacy of force production is reduced in lengthening muscle. 3. Single-unit recruitment patterns were found to be qualitatively similar in isometric and lengthening contractions. In each case, motor units were recruited in order of increasing spike voltage. The numbers of newly recruited units declined steeply with each successive increment in active force. For a given unit, the force at which recruitment occurred was found to be greater in lengthening contractions than in isometric contractions, and in lengthening contractions it was also found to depend on the level of initial force. 4. Two patterns of motor-unit rate modulation were observed during muscle stretch, depending on whether a given unit was firing before the beginning of stretch or whether it was recruited during the course of stretch. Motor units that were active prior to stretch were found to increase firing rate at stretch onset and to vary their rate very little thereafter. Motor units recruited in the course of stretch began firing at an initial rate proportional to their force threshold, gradually increased their firing rate with increasing force, and sometimes reached an apparent maximum rate. 5. These results are discussed in terms of the mechanical properties of lengthening muscle and reflex regulation of these properties. Each identified pattern of motor-unit recruitment and rate modulation is evaluated for its potential contribution to the regulation of muscle properties, especially the prevention of muscle yield. We conclude that at low to moderate levels of initial force, recruitment of new motor units is likely to be the most effective compensatory mechanism.
Further morphological and electrophysiological studies on snake muscle spindles
Authors: Fukami Y.
Published: December 2017

1. Electron microscope studies using ruthenium red, horseradish peroxidase, and colloidal lanthanum disclosed a feature characteristic of the snake spindle capsule: it consists of a single layer of flattened cells connected in series, each of which forms a cylinder enclosing the intrafusal fiber. 2. In intact spindles none of the markers penetrated the capsule. The diffusion barrier appeared to be located along the intercellular space near the inner surface of the capsule layer. Through the openings at the ends of the capsule the marker gained access to the periaxial space, but only for a limited distance. 3. Through a punctured hole in the capsule, ruthenium red had access to the periaxial space, disclosing a dense network consisting of fine filaments and granular structures. Since this space was also shown to contain alcian blue-positive substrate, the network may represent acid mucopolysaccharide (probably hyaluronic acid + protein molecules), which may account for the observed limited longitudinal diffusion of this dye in the periaxial space. The intercellular space between the intrafusal fiber, the sensory ending, and the satellite cell was filled with ruthenium red, and no special junction was found between these cells. 4. Using glass microelectrodes, potential profiles across the sensory region of muscle spindles of the snake were examined. 5. When the electrode was advanced through the capsular region, two steps of negative potential were usually observed. The first negative step of 5-10 mV was confirmed by fluorescent dye injection to be due to penetration of the capsule. The second larger step of 40-60 mV negative to the bathing solution was demonstrated by the dye injection to be due to penetration of the intrafusal fiber. Occasionally, a negative potential of 20-30 mV relative to the bathing solution was also recorded. This potential, characterized by small spikelike potentials occurring in synchrony with nerve impulses, was considered to be due to penetration of the sensory ending. 6. both the capsule and the intrafusal fiber showed rectification to injected currents. From input resistance, input capacitance and surface area specific resistance and capacitance were estimated with some assumptions to be 4.1-4.8 k omega . cm2 and 5.1-14.3 micro F/cm2 for the capsule, and 1.1-2.8 k omega . cm2 and 11-23 micro F/cm2 for the intrafusal fiber. The intrafusal fiber of short-capsule spindles lacked an action potential, whereas that of long-capsule spindles responded with an all-or-none action potential to depolarizing current. 7. In about half of the short-capsule spindles examined (8/15), current injected through an intracellular electrode in the intrafusal fiber neither initiated impulses in the afferent axon nor affected background nerve activity. The rest of the spindles responded to depolarizing current with initiation of nerve impulses and concomitant maintained contraction of the intrafusal fiber during applied current...
Topographic coding of olfactory quality: odorant-specific patterns of epithelial responsivity in the salamander
Authors: Mackay-Sim A. , Shaman P. , Moulton D. G.
Published: December 2017

1. Electrophysiological recordings were made on the ventral olfactory epithelium of the salamander Ambystoma tigrinum in order to investigate whether individual odorants can elicit unique patterns of receptor neuron responses. 2. Slow transepithelial voltage transients, Veog(-), were recorded from 30 sites on each epithelium. For each odorant a topographic pattern was derived from the Veog(-) amplitudes across the 30 recording sites. 3. Nine odorants were tested, each in seven animals, and topographic patterns of Veog(-) amplitudes were drawn for each animal. Due to the morphological variability among animals, the electrode sites for each animal were assigned to six epithelial regions for which responses were then compared by analysis of variance. 4. Odorant-specific regional differences in responsivity were observed. The odorants can be grouped according to the similarity of the topographic distributions of responses elicited by them. We observed that no two odorants elicited exactly the same response patterns. This suggests that olfactory receptor neurons with similar responses are grouped together in the same region of the epithelium. 5. Dramatic differences in responsivity among the various epithelial regions, irrespective of the test odorant, were also noted. This observation may be due to regional differences in receptor neuron density or overall sensitivity. 6. It is concluded that differences between the topographic distributions of receptor cell responses, elicited by the nine test odorants, permits these responses to be discriminated as unique patterns of information at the olfactory bulb.