Journal of Neurophysiology

Maeda, M.; Magherini, P. C.; Precht, W.

doi: N/Apmid: 191572

Abstract 1. Intracellular responses in neck and forelimb motoneurons to electrical stimulation of the vestibular nerve, the optic tectum, and the optic nerve were studied in frog. 2. Stimulation of the anterior branch of the vestibular nerve typically produced EPSPs, bilaterally, in neck, shoulder (DOR), and forelimb extensor (TRI, RAD) motoneurons, and bilateral IPSPs in forelimb adductor (PED) and flexor (ULN, COR) motoneurons. 3. Latencies of PSPs recorded in neck, shoulder, and proximal extensor motoneurons (TRI) were mostly in the disynaptic range, whereas many of those recorded in distal extensor (RAD) and in adductor and flexor motoneurons involved three synapses. 4. Lesion of the vestibulospinal fibers greatly reduced the vestibular nerve-evoked field potentials in the spinal cord and the occurrence of PSPs in forelimb motoneurons. These results as well as the latency measurements suggest that the pathway linking vestibular nerve and forelimb motoneurons mainly consists of vestibulospinal fibers, though involvement of other structures for production of later PSPs could not be completely ruled out. Hemisection of the brain stem at its most caudal level showed that the pathway to the contralateral motoneurons crosses at the level of brain stem as well as in the spinal cord. 5. Stimulation of the optic tectum produced EPSPs, IPSPs, and a mixture of EPSPs and IPSPs in neck, shoulder, and forelimb motoneurons, bilaterally. Most frequently, a combination of an excitation and inhibition was observed. The pathway from the optic tectum to neck and limb motoneurons is at least dysnaptic in nature. 6. Stimulation of the optic nerve produced IPSPs and a mixture of EPSPs and IPSPs in neck and forelimb motoneurons. Impulses originating from the optic nerve descend as far as to lumbar motoneurons producing EPSP-IPSP sequences bilaterally. 7. Interaction studies suggested that the vestibular and optic pathways to neck and forelimb motoneurons are separate from each other so that the site of integration of vestibular and visual input occurs at the level of motoneurons. 8. Evidence for electronic coupling among forelimb motoneurons and electrical synaptic transmission in th pathway linking vestibular nerve and forelimb motoneurons is presented. Copyright © 1977 the American Physiological Society

McIlwain, J. T.

doi: N/Apmid: 845621

Abstract 1. Electrical stimulation in areas 17, 18 and 19 of the cat's visual cortex activated neurons in the superficial gray layer of the superior colliculus. The threshold for such excitation was lowest when the receptive fields of cells at the stimulus site lay inside the receptive field of the collicular cell under observation. 2. A substantial percentage of the recorded collicular cells received convergent excitatory input from more than one of the stimulated cortical areas. When stimuli could be applied in parts of areas 17, 18, and 19 related retinotopically to a collicular cell, over half of the units were activated from all three cortical areas by low-intensity stimulation. 3. Cells located near one another in the colliculus received excitatory cortical input from regions of areas 17, 18, and 19 which were not identical in size. This may be attributable to the disparate dimensions of collicular dendritic fields, which permit neighboring cells to sample dissimilar regions of the topographically organized cortical input. It is argued that this projection system preserves the functional unity of cortical and tectal cell groups processing information from a given retinal point. Copyright © 1977 the American Physiological Society

Kenshalo, D. R.; Duclaux, R.

doi: N/Apmid: 403250

Abstract 1. The receptive fields of 48 specific cold units, located in the hairy and glaborous skin of fore- and hindlimbs of rhesus monkeys, were mapped and scale drawings made. Forty-five percent had single spotlike receptive fields of 1-2 mm diameter or were up to 2 mm wide and 3-5 mm long, and formed straight, crescent, or right-angle shapes. The remaining 55% had two to five discrete spots or small areas innervated by a single fiber. Area or number of receptive fields per unit did not vary significantly along the limb axis. 2. Of the 48 specific cold units, 15 were held sufficiently long to record their dynamic responses to intensity-rate series of temperature changes from several adapting temperatures (ATs) between 20 and 45 degrees C. Six cold units showed a paradoxical increase in the steady-state response at the 45 degrees C compared to that at the 40 degrees C AT. Of the 15 cold units, 7 discharged in bursts at the 35 degrees C or lower ATs. The proportion of short intervals (intraburst intervals) increased as the adapting temperature decreased. 3. Both the latency and the temperature change at the onset of the dynamic response to cooling remained relatively constant for ATs up to and including 35 degrees C. The response latencies were approximately 200-400 ms, while the temperature changes at response onset were -0.02 to -0.06 degrees C. Both increased sharply at the 40 degrees C and still more at the 45 degrees C ATs. 4. The rate of increase in the frequency of the dynamic response to cooling by the fast rate increased to maximum at the 30 degrees C AT and then decreased at the higher ATs. For the slow rate the highest rate of increase in frequency occurred at the 20 degrees C AT. The fast rate of cooling always induced a faster rate of increase in frequency than slow rate of cooling. 5. Four indices of response magnitude were used in the analysis of the dynamic responses. These were peak frequency, cumulative impulses in the first 4 s following stimulus onset, average frequency during stimulations plus 3 s, and the total impulses during stimulation. The first three indices gave similar representations of the dynamic responses to the rate and intensity of cooling and the effect of the AT. The slow rate of cooling invariably yielded a smaller index of response magnitude than the fast rate. The difference became more pronounced as the intensity of cooling increased. The stimulus intensity-response magnitude functions were nonlinear. This nonlinearity was more pronounced at the low than at the high ATs. As the AT was increased, the response indices approached linearity at the 35 and 40 degrees C ATs. The greatest sensitivity of cold units to cooling was from the 35 degrees C AT. The fourth index, total impulses during stimulation minus steady state, gave a different picture. This index of response magnitude was linearly related to stimulus intensity for both rates of cooling from all adapting temperatures except for the slow rate of cooling from the 45 degrees C AT... Copyright © 1977 the American Physiological Society

Gardner, D.

doi: N/Apmid: 845626

Abstract 1. The 26 identified neurons of Aplysia buccal ganglia include 4 interneurons and their follower cells. Each interneuron makes cholinergic synaptic connections on eight identified ipsilateral follower neurons. Each interneuronal action potential also produces a zero-latency, Mg-intensitive electrotonic coupling potential in one cholinergic and electrotonic input from the interneurons. Electrotonic connections are bidirectional and nonrectifying. 2. Ipsilateral pairs of interneurons receive extensive common synaptic input from several unidentified neurons: each interneuron also receives some input not received by the other. These pairs are linked by bidirectional nonrectifying electronic coupling which is insensitive to high Mg. As a consequence of this organization, ipsilateral interneuron pairs can fire a) independently, or b) synchronously, or c) one active interneuron can depolarize the other. 3. Each follower receiving synaptic input from one ipsilateral interneuron also receives similar input from the other interneuron. Common follower cells thus receive a) asynchronous PSPs, or b) large summated PSPs, or c) an increased number of PSPs from each interneuron. The latter two modes constitute feed-forward summation of interneuronal action. 4. Interneuronal output is confined to ipsilateral neurons. Symmetric pairs of interneurons are coordinated by common inputs and are not directly interconnected by either chemical or electrotonic synapses. Synchrony of firing of symmetric pairs is, therefore, looser than that of ipsilateral pairs. Copyright © 1977 the American Physiological Society

Karowski, C. J.; Proenza, L. M.

doi: N/Apmid: 845622

Abstract 1. In the Necturus retina, light-evoked field potentials, Muller (glial) cell responses, and extracellular potassium ion concentration (K+0) were recorded and found to exhibit the three-way correlation characteristic of these variables elsewhere in the nervous system. 2. Muller cell responses to a flashed spot or annulus consist primarily of slow depolarizations at both light onset and offset. The responses are maximum to 0.5-mm-diameter spots and decrease with larger diameters. Responses to stimulus intensity and flicker were also used to characterize Muller cell behavior. 3. In response to long-duration stimuli, the initial Muller cell depolarization is followed by a very slow hyperpolarization, which is likely the origin of slow PIII. 4. A new extracellular potential is described, the M-wave, the basic properties of which suggest that it is generated by Muller cells. Moreover, the M-wave and Muller cells show remarkably similar behavior to a wide variety of stimulus parameters. 5. In the proximal retina, K+0 increases at both light onset and offset with a time course similar to that of Muller cell depolarizing responses. This K+ increase also behaves similarly to the Muller cell depolarization in response to changes in stimulus parameters. 6. It is concluded that light stimulation leads to an increase in K+0 in the proximal retina and that this increase depolarizes Muller cells whose associated currents, in turn, generate the M-wave. Copyright © 1977 the American Physiological Society

Tsuchitani, C.

doi: N/Apmid: 845625

Abstract 1. Single-unit discharges to auditory stimuli were recorded extracellularly from superior olivary complex (SOC) units located lateral to the medial superior olive. Stimuli consisted of monaurally or binaurally presented tone bursts. The response measures obtained were effective ear, nature of effect, stimulus-frequency representation, maximum output, latency of response, and temporal pattern of tone burst-elicited discharges. Electrolytic marks were made at the unit studied or at the end of the electrode tract and in the medial superior olive. Following each experiment the locations of the units studied were determined histologically. An atlas of the laterally located SOC cell groups was developed to permit classification of units on the basis of localization within cell groups. Units were also classified according to the effects of stimulating the two ears. 2. All SOC units located lateral to the medial superior olive were excited by stimulation of the ipsilateral ear. Stimulation of the contralateral ear either excited, inhibited, had no effect, or had a potentiating effect on the discharges elicited by stimulating the ipsilateral ear. 3. Most lateral superior olivary (LSO) units were inhibited by contralateral stimulation, were narrowly tuned, produced low to high levels of maximum output, had short latencies, and produced regular discharge patterns characterized by chopper PST histograms with narrow initial peaks. 4. Most units within the caudal margins of the LSO (pLSO) were not affected or were inhibited by a contralateral stimulus; many were broadly tuned and exhibited intensity functions with large dynamic range and low slope. These units also had long latencies and produced chopper PST histograms with wide initial peaks. 5. Most units located dorsal to the LSO (DPO and DLPO) were not affected by the contralateral stimulus, were narrowly tuned, produced moderate levels of maximum discharge, had long latencies, and produced chopper PST histograms with wide initial peaks. 6. Units located ventral to the LSO appeared to have response characteristics related to unit location. Most units below the ventral hilum of the LSO (VLPO) were inhibited by the contralateral stimulus and many were broadly tuned VLPO units produced wide or poorly defined narrow-chopper discharge patterns and intensity functions with high maximum output. Most units located ventral to the lateral loop of the LSO (LNTB) were not affected by the contralateral stimulus and had response characteristics that may be related to the rostrocaudal location of the unit. 7. The cell groups located dorsal and ventral to the LSO were tonotopically organized with low-frequency-sensitive units located laterally and high-frequency-sensitive units located medially. The units located along the caudal margins of the LSO had a tonotopic organization similar to that of the LSO. Copyright © 1977 the American Physiological Society

Beall, J. E.; Applebaum, A. E.; Foreman, R. D.; Willis, W. D.

doi: N/Apmid: 403249

Abstract 1. Negative intermediary cord potentials and the equivalent field potentials were recorded from the surface or within the monkey lumbosacral spinal cord in response to stimulation of myelinated afferent fibers in cutaneous or mixed nerves of the hindlimb. 2. Cord potentials resembling the N1 and N2 potentials described in the cat spinal cord were found but, in addition, activation of small myelinated fibers produced a later potential named here the N3-wave. By use of a subtraction technique, it is estimated that the N3-wave has a latency of 11.4 (+/- 3.5 SD) ms from the time of arrival of the volley in the largest affs at 9 (+/- 3) ms after its onset, and the wave lasts 23 (+/- 5.7) ms. 3. The N3-wave is not lost following spinal cord transection, but may instead be enhanced. It is thus due to neural circuitry intrinsic to the lumbosacral spinal cord. 4. The longitudinal distribution of the N3-wave is similar to that of the N1- and N2-waves. 5. The field potential associated with the N3-wave and recorded from within the spinal cord has two negative foci in some animals: near the dorsalmost part of the dorsal horn and in an area equivalent to Rexed's laminae IV-VI. The field potential reverses in sign in the ventral horn. 6. The N3-wave is evoked by Adelta fibers. This was shown by grading the stimulus strength, by measuring the conduction delay for producing the wave when stimuli are applied either proximally or distally on the sural nerve, and by showing that the N3-wave persists when the Aalphabeta fibers are anodally blocked. 7. There is often a late burst discharge in spinal neurons, including spinothalamic tract neurons, which can be attributed to Adelta fibers and which corresponds in time to the N3-wave. 8. It is proposed that the N3-wave can be used as a monitor of the central effects of Adelta fibers in the spinal cord. Copyright © 1977 the American Physiological Society

Lynch, J. C.; Mountcastle, V. B.; Talbot, W. H.; Yin, T. C.

doi: N/Apmid: 403251

Abstract 1. Experiments were made on the cortex of the inferior parietal lobule in 10 hemispheres of six alert, behaving monkeys. The electrical signs of the impulse discharges of single cortical cells were recorded as the monkeys executed tasks requiring them to fixate stationary visual targets, track those which moved slowly, and to make saccadic movements to foveate those which suddenly jumped from one locus to another within the field of view. A total of 907 neurons of area 7 were identified in terms of their physiological properties, particularly the correlation of their activity with the oculomotor components of these behavioral acts of directed visual attention; 480 of these were located by cytoarchitectural layer. Most identifiable cells of area 7 are visuomotor neurons, in a special and conditional sense. Their discharge frequencies increase before and during those steady fixations and movements of the eyes which secure and maintain foveation of objects, but only if the visual targets engaged are linked by a strong motivational drive; in our experiments, one between thirst and the light whose dimming the animal has learned to detect for liquid reward. We have identified and studied three major classes of neurons in area 7. 2. The visual fixation neurons (57%) accelerate discharge synchronously with fixation of a visual object the animal desires. The incremented discharge continues until reward, but then declines abruptly even when there is no immediate shift of the line of gaze. Fixation neurons are relatively inactive during those casual fixations by which the animal insepcts the surrounding environment. Mist fixation neurons subtend gaze fields limited to one quadrant or half of the total gaze field. The sum of the gaze fields of the fixation neurons in one hemisphere is weighted moderately toward the contralateral side. Fixation cells also discharge during slow pursuit movements in any direction so long as the movement stays within the gaze field of the neuron under study. About 40% of fixation cells are suppressed before and during saccadic movements of the eyes to a new target within the gaze field of the fixation cell. Those suppressed are located preferentially in layer V of the cortex. Suppression is maximal for saccades directed contralaterally to the hemisphere under study. 3. Visual tracking neurons are active during oculomotor pursuit of slowly moving visual objects, not during steady fixations. They show a marked directional but no laterality relation, and are suppressed before and during a visually evoked saccade superimposed on the smooth pursuit movement. The rate of discharge is a flat function of tracking speed so that these cells do not appear to emit signals which specify the speed of smooth pursuit movements. 4. The saccade neurons are active before and during visually evoked saccadic movements of the eyes but not before spontaneous saccades, no matter whether made in light or near darkness. The discharge of saccade neurons leads the eye movement by as much as 150 ms (mean, 73 ms)... Copyright © 1977 the American Physiological Society

Mori, S.; Shik, M. L.; Yagodnitsyn, A. S.

doi: N/Apmid: 845624

Abstract 1. An attempt has been made to elucidate how direct stimulation of the mesencephalic locomotor region (MLR, with Horsley-Clarke coordinates P2, L4, and H0) is transmitted through the pons to the spinal cord where a stepping generator is presumed to exist. 2. A longitudinal strip, termed the "pontine locomotor region" (PLR), was identified. It extends ventrocaudally throughout the lateral pontine tegmentum (P3-P9, L4 and about 2 mm beneath the floor of the IVth ventricle). 3. Stimulation of this locomotor strip at P4-5 and P8-9 levels generated hindlimb stepping or four-legged locomotion on a treadmill similar to that elicited by MLR stimulation. However, "PLR stepping" was more often accompanied by spasticity of the hindlimbs. Stimulation of the pontine strip at the P6-7 level produced stepping accompanied by an opening of the mouth. 4. Subthreshold MLR stimulation together with subthreshold PLR stimulation generated locomotion. Ipsilateral and contralateral MLR-PLR stimulations were of equal effectiveness for the generation of locomotion. 5. Stimulation of rostral (P3-6), but not caudal (P6-9), parts of the PLR evoked field potentials in the MLR with two negative components. The points at which these potentials were evoked with minimum current were usually coincident with the best points for eliciting locomotion. Short-latency monophasic negative potentials were evoked in the rostral part of the PLR by MLR stimulation. 6. Locomotion elicited by stimulation of either the MLR or the PLR was suppressed by stimulation within a midpontine region, 1.5-2.0 mm beneath the floor of the IVth ventricle (P6-7, L0-0.5, H-5 to -6). Stimulation applied to the close vicinity of this "inhibitory" region did not evoke field potentials in the MLR. 7. In some animals stimulation between the inhibitory region and the underlying PLR could facilitate locomotion elicited by MLR stimulation, although no stepping was produced by such stimulation alone. Copyright © 1977 the American Physiological Society

Spear, P. D.; Smith, D. C.; Williams, L. L.

doi: N/Apmid: 845627

Abstract 1. Visual receptive-field characteristics were determined for 154 cells in the ventral lateral geniculate nucleus (VLG) of cats anesthetized with nitrous oxide. All cells were verified histologically to be within the VLG. Responses of 182 cells from laminae A and A1 of the dorsal lateral geniculate nucleus (DLG) were tested for comparison. 2. The VLG cells could be grouped into one of seven classes according to their responses to light stimulation. Twenty-seven percent of the cells had uniform receptive fields. They responded maximally to stationary stimuli flashed on or off anywhere within the receptive field and showed no evidence for antagonistic surround mechanisms. About 19.5% of the VLG cells had concentric receptive fields. They were similar to the uniform type, with the addition of a concentric inhibitory surround. Eight percent of the VLG cells had ambient receptive fields. These cells were characterized by an unusually regular maintained discharge which varied in rate in relation to the level of receptive-field illumination or of full-field ambient illumination. About 4% of the VLG cells were movement sensitive. They gave little or no response to stationary stimuli flashed on or off in the receptive field, and responded best to a contour moving across the receptive field in any direction. An additional 2.5% of the VLG cells were direction sensitive. Their response was dependent on the direction of stimulus movement through the receptive field. Sixteen percent of the VLG cells had indefinite receptive fields. They responded to whole-eye illumination or to localized visual-field stimulation; however, specific receptive-field properties could not be adequately defined. Approximately 23% of the VLG cells studied gave no convincing response to visual stimulation. 3. Responses of DLG cells agreed with those reported in previous studies. Almost all (97%) had concentric receptive fields, and a few (3%) had uniform receptive fields with no apparent antagonistic surround. None of the DLG cells had receptive fields like those in the other classes found for VLG cells. 4. The VLG cells tended to have large receptive fields; mean diameter was 10.6 degrees of visual arc. This was substantially larger than the diameter of receptive fields for DLG cells. In addition, VLG cells generally required larger stimuli than DLG cells to respond. There was no consistent relationship between receptive-field size and visual-field eccentricity for VLG cells, in contrast to the DLG. Most (57%) VLG cells were driven only by the contralateral eye, 30% were binocularly driven, and 13% were driven only by the ipsilateral eye. 5. A systematic visuotopic organization was present in the VLG. The lower visual field was represented anteriorly in the nucleus and the upper visual field posteriorly. The vertical meridian was represented along the dorsomedial border of the VLG where it abuts the DLG, and the temporal periphery was represented ventrolaterally. 6. Responses to electrical stimulation of the optic chiasm were studied for 55 VLG cells... Copyright © 1977 the American Physiological Society