Showing papers in "Journal of Neurophysiology in 1975"

Posterior parietal association cortex of the monkey: command functions for operations within extrapersonal space

Abstract: Experiments were made on the posterior parietal association cortical areas 5 and in 17 hemispheres of 11 monkeys, 6 M. mulatta and 5 M. arctoides. The electrical signs of the activity of single cortical cells were recorded with microelectrodes in waking animals as they carried out certain behavioral acts in response to a series of sensory cues. The behavioral paradigms were one for detection alone, and a second for detection plus projection of the arm to contact a stationary or moving target placed at arm's length. Of the 125 microelectrode penetrations made, 1,451 neurons were identified in terms of the correlation of their activity with the behavioral acts and their sensitivity or lack of it to sensory stimuli delivered passively; 180 were studied quantitatively. The locations of cortical neurons were identified in serial sections; 94 penetrations and 1,058 neurons were located with certainty. About two-thirds of the neurons of area 5 were activated by passive rotation of the limbs at their joints; of these, 82% were related to single, contralateral joints, 10% to two or more contralateral joints, 6% to ipsilateral, and 2% to joints on both sides of the body. A few of the latter were active during complex bodily postures. A large proportion of area 5 neurons were relatively insensitive to passive joint rotations, as compared with similar neurons of the postcentral gyrus, but were driven to high rates of discharge when the same joint was rotated during an active movement of the animal...

Theory of current source-density analysis and determination of conductivity tensor for anuran cerebellum

Abstract: The theoretical basis of current source-density (CSD) analysis in the central nervous system is described. Equations relating CSD, the current flow vector, and the extracellular field potential are given. It is shown that the CSD provides superior resolution of neuronal events when compared to conventional field-potential analysis. Expressions for the CSD in rectangular Cartesian coordinates are derived, including the general case of anisotropic, inhomogeneous conductive tissue, and a coordinate system rotated with respect to the principal axes (APPENDIX). The minimum number of spatial dimensions for accurate CSD analysis is discussed. The conductivity tensor was experimentally measured in frog and toad cerebella. All three principal components of the tensor were evaluated and their spatial gradients determined to be negligible. It was also shown that the conductivity was independent of potential. Thus the anuran cerebellum is anisotropic, homogeneous, and ohmic. On the basis of these results the appropriate mathematical expression for the CSD was selected.

Representation of cochlea within primary auditory cortex in the cat.

Abstract: The representation of sound frequency (and of the cochlear partition) within primary auditory cortex has been investigated with use of microelectrode-mapping techniques in a series of 25 anesthetiz...

Responses to visual stimulation and relationship between visual, auditory, and somatosensory inputs in mouse superior colliculus.

Abstract: The superior colliculus was studied in anesthetized mice by recording from single cells and from unit clusters. The topographic representation of the visual filed was similar to what has been found in other mammals, with the temporal part of the contralateral visual field projecting posteriorly and the inferior visual field projecting laterally. At the anterior margin of the tectum receptive fields recorded through the contralateral eye and invaded the ipsilateral visual hemifield for up to 35 degrees, suggesting that the entire visual field through one eye is represented on the contralateral superior colliculus. Cells located closest to the tectal surface had relatively small receptive fields, averaging 9 degrees in center diameter; field sizes increased steadily with depth. The prevailing cell type in the stratum zonal and superficial gray responded best to a small dark or light object of any shape moved slowly through the receptive-field center or to turning a small stationary spot on or off. Large objects or diffuse light were usually much less effective. Less than one-quarter of superficial layer cells showed directional selectivity to a moving object, the majority of these favoring up and nasal movement. The chief visual cell type in the stratum opticum and upper part of the intermediate gray resembled in the newness neurons described for many other vertebrates: they had large receptive fields and responded best to up and nasal movement of a small dark or light object, whose optimal size was similar to the optimum for upper-layer cells. If the same part of the receptive field was repeatedly stimulated there was a marked tendency to habituate. Only very few cels responded to the ipsilateral eye. Intermixed with visual cells in the upper part of the intermediate gray were cells that responded to somatosensory or auditory stimuli. Here bimodal and trimodal cells were also seen. In deeper layers somatosensory and auditory modalities tended to take over. These two modalities were not segregated into sublayers but rather seemed to be arranged in clusters. Responses to somatosensory and auditory stimuli were brisk, showing little habituation to repeated stimulation.

Experimental optimization of current source-density technique for anuran cerebellum.

Abstract: This paper represents a systematic, semirigorous attempt to optimize the technique of current source-density (CSD) analysis experimentally. We compared different spatial differentiation formulas in...

Nonspiking interneurons in walking system of the cockroach.

Abstract: Intracellular recordings were made from the neurites of interneurons and motoneurons in the metathoracic ganglion of the cockroach, Periplaneta americana Many neurons were penetrated which failed to produce action potentials on the application of large depolarizing currents Nevertheless, some of them strongly excited and/or inhibited slow motoneurons innervating leg musculature, even with weak depolariziing musculature, even with weak depolarizing currents Cobalt-sulfide-straining of these nonspiking neurons showed them to be interneurons with their neurites contained entirely within the metathoracic ganglion Two further characteristics of these interneurons were rapid spontaneous fluctuations in membrane potential and a low resting membrane potential One nonspiking neuron, interneuron I, when depolarized caused a strong excitation of the set of slow levator motoneurons which discharge in bursts during stepping movements of the metathoracic leg During rhythmic leg movements the membrane potential of interneuron I oscillated with the depolarizing phases occurring at the same time as bursts of activity in the levator motorneurons No spiking or any other nonspiking neuron was penetrated which could excite these levator motoneurons From all these observations we conclude that oscillations in the membrane potential of interneuron I are entirely responsible for producing the levator bursts, and thus for producing stepping movements in a walking animal During rhythmic leg movements, bursts of activity in levator and depressor motoneurons are initiated by slow graded depolarizations The similarity of the synaptic activity in these two types of motoneurons suggests that burst activity in the depressor motoneurons is also produced by rhythmic activity in nonspiking interneurons The fact that no spiking neuron was found to excite the depressor motoneurons supports this conclusion Interneuron I is also an element of the rhythm-generating system, since short depolarizing pulses applied to it during rhythmic activity could reset the thythm Long-duration current pulses applied to interneuron I in a quiescent animal did not produce rhythmic activity This observation, together with the finding that during rhythmic activity the slow depolarizations in interneuron I are usually terminated by IPSPs, suggests that interneuron I alone does not generate the rhythm No spiking interneurons have yet been enccountered which influence the activity in levator motoneurons Thus, we conclude that the rhythm is generated in a network of nonspiking interneurons The cellular mechanisms for generating the oscillations in this network are unknown Continued

Unit activity in vestibular nucleus of the alert monkey during horizontal angular acceleration and eye movement

Abstract: Single units were recorded from the vestibular nuclei of unanesthetized monkeys that were rotated in the horizontal plane while simultaneously pressing individual buttons in a controlled array which turned with hem. Using this behavioral paradigm, it was possible to 1) determine the relationship of unit discharge to eye movements measured by the DC-coupled electrooculogram and calibrated by the button-press task, and 2) determine the relationship of unit discharge to horizontal acceleration, either with or without the compensatory eye movements evoked by vestibular stimulation. Based on their responses during vestibular stimulation and/or eye movements, neurons in the vestibular nuclei (77% of our sample was in the medial nucleus) could be divided into four groups...

Morphology and distribution of muscle spindles in dorsal muscles of the cat neck.

Abstract: Silver-stained sections have been examined from the five dorsal neck muscles splenius, biventer, cervicis, complexus, rectus capitis major, and occipitoscapularis. Every serial section was examined for at least one muscle of each type so that a complete description of the spindle distribution and morphology could be made. With the exception of occipitoscapularis (whose prime function is probably in scapula rotation and not in head movement), neck muscles have a remarkably high spindle density. Occipitoscapularis has a spindle density similar to that of hindleg locomotor muscles (13-19 per gram), but splenius has a density of 46-66 per gram, biventer cervicis 74-96 per gram, complexus 71-107 per gram, and rectus capitis major 48-84 per gram. Such high densities have only previously been seen in small muscles whose total spindle population is not large. Because of the relatively large size of some neck muscles, individual muscles with a spindle content of up to 254 spindles have been found.

Slowly adapting receptors in cat knee joint: can they signal joint angle?

Abstract: Afferent activity in the lateral (LAN), medial (MAN), and posterior (PAN) articular nerves supplying the cat knee joint was studied at intermediate positions of the joint that included most of its working range. The discharge was analyzed only while the joint was stationary. The small LAN showed negligible tonic activity at intermediate angles (as determined by gross recording) and was not studied further.

Capacities of humans and monkeys to discriminate vibratory stimuli of different frequency and amplitude: a correlation between neural events and psychological measurements.

Abstract: The capacities of monkeys and humans to discriminate between mechanical sinusoids differing in amplitude or frequency were measured in a two-alternative, forced-choice task. The difference limen fo...

Extraction of sleep-promoting factor S from cerebrospinal fluid and from brains of sleep-deprived animals.

Abstract: Sleep-promoting factor (factor S) was extracted, partially purified, and concentrated from cerebrospinal fluid and from acid-acetone extracts of brain stem anc cortex of sleep-deprived goats and sheep. 2. Solutes greater than 500 daltons were largely removed by serial ultrafiltrations through molecular sieves (Amicon membranes UM10 and UM05); solutes less than 350 daltons were largely eliminated by gel filtration through Sephadex G10 columns. Sleep-promoting activity was found in a fraction eluted prior to [14C] sucrose marker. 3. Concentrated fraction were infused intraventricularly in rats (0.1 ml in 30 min just prior to 12-h dark cycle) and in rabbits (0.3 ml in 90 min in morning). Sleep-promoting activity was assayed by decrease in nocturnal locomotor activity of rats and by duration and amplitude of slow-wave cortical EEG in rabbits.

Inferior colliculus. I. Comparison of response properties of neurons in central, pericentral, and external nuclei of adult cat.

Abstract: The responses of 150 units in the central (ICC), pericentral (ICP), and external nuclei (ICX) of the inferior colliculus of the anesthetized cat were studied in relation to their tuning characteristics and binaural responses to tonal stimuli. Units in ICC were characterized by sharp tuning and binaural responses, while those in ICP and ICX were frequently very broadly tuned with a poorly defined best frequency. Nonetheless, in the latter nuclei a tendency existed for tonotopic organization to occur with high frequencies located externally and low frequencies at the margins of the central nucleus. Tuning measurements were hampered by the common occurrence of habituation in the discharges of single units in ICP and, to a lesser extend, ICX. The majority of units in ICP could be differentiated from those in ICX by their monaural input. Speculations were advanced linking anatomical cell types to physiological responses in the three nuclei and into the possible functional significance of the different behavior of units to tonal stimuli.

Activity of single motor units from human forearm muscles during voluntary isometric contractions

Abstract: 1. Microelectrode recordings from single motor units of the first dorsal interosseus and the extensor indicis muscles of normal human subjects were studied during voluntary, isometric contractions. The conduction velocity of the nerve fiber innervating the muscle unit was used as an estimator of the size of the motoneuron. 2. During slowly increasing contractions, the units were recruited at force levels which were closely correlated to conduction velocity. The units associated with low conduction velocity were recruited first, those with high conduction velocity, last. 3. If small, stepwise force increments were used instead of slowly, continuously increasing contractions, the units were first activated during the steps and became inactive during the subsequent plateaus. If higher steady-force levels were reached, the activity was maintained also during the plateaus. This steady force, where a unit remained continuously active independent of the rate of rise of tension, represents its tonic threshold. 4. The tonic threshold is positively correlated with conduction velocity, as is the threshold force of recruitment. As a consequence, high-threshold units have a large force range below tonic threshold where they can only be transiently activated, whereas low-threshold units have a large physiological force range above tonic threshold where they operate tonically. The phasic or tonic appearance of discharge pattern reflects quantitative differences in tonic threshold between units of different size. All units examined could be activated phasically (below) and tonically (above tonic threshold). No evidence was found indicating the existence of two qualitatively different classes of units corresponding to a tonic and phasic type, although both muscles investigated consist of about equal numbers of type I and type II muscle fibers. 5. The change in firing rate per unit force was inversely related to conduction velocity: the slower conducting units showed larger changes in firing rate per unit force than faster conducting units. This corresponds to the larger excitability of the smaller units indicated by their earlier recruitment. 6. The data of this study are consistent with the hypothesis that the functional characteristics of human motoneurons are determined by the graded excitability of motoneurons according to size.

Discrimination of odors in olfactory bulb, pyriform-amygdaloid areas, and orbitofrontal cortex of the monkey

Abstract: In the orbitofrontal olfactory area (LPOF) which was delineated in a previous paper, the capacity for odor discrimination was studied and compared with that in the anterior pyriform cortex (AP), the medial portion of the amygdala (MA), and the olfactory bulb (OB). Unanesthetized monkeys were used and eight odors were applied. 1. In the OB, 12.5% of the cells responded to only one odor, and the cells which responded to five odors were most numerous (25%). The total of the cells which responded to two, three, and four odors was 52%, which was less than the total of the cells responding to three, four, and five odors (67.5%). A small number oc cells responded to all eight odors (2.5%). The responses were classified as an increase (+type), a decrease (-type), or no change (no-type) in the rate of spike discharge. 2. In the AP and MA, no difference in the response patterns was found. The cells which responded to only one odor were 12.3% of the total, and the cells which responded to three different kinds of odors were most numerous (34.3%). The total of the cells responding to two, three, and four odors was 80%, much more than that in the OB. In addition, no cell responded to all eight odors. Concerning the response types, an increase followed by a decrease, or vice versa, in the rate of spike discharges (mixed-type) was observed which did not appear in the OB. Thus, an advance was found in the processing of olfactory information when compared with the OB. 3. A most striking finding in the LPOF was that 50% of the cells responded to only one odor. The cells which responded to two, three, and four odors decreased in this order, and no cell responded to more than five odors. These cells never responded to light or sound. 4. Using three very similar odors and five very different odors, it was apparent that the ability to discriminate odors of the same category is far more advanced in the LPOF than in the lower olfactory areas; and, in contrast, the lower olfactory areas also play a significant role in the discrimination of odors which belong to different categories. 5. It was concluded that the capacity for odor discrimination definitely improves along the olfactory nervous system from the lower to the higher areas. It is highly probable that a fine and sepcific discrimination of odors is performed in the LPOF.

Receptive-field characteristics of single neurons in lateral suprasylvian visual area of the cat.

Abstract: The visual receptive fields of 213 cells in the lateral suprasylvian visual cortex (LS, or Clare-Bishop area) were studied in cats anesthetized with nitrous oxide. Eighty-one percent of the cells were directionally selective. They responded poorly to stationary stimuli flashed on or off, but gave a directionally selective response to stimuli moving through the receptive field. Most of these had a single preferred direction and an opposite null direction. They typically responded to a range of directions of stimulus movement from 45 to 90 degrees to either side of the preferred direction. Small stimuli (1-2 degrees or smaller) typically were effective and 87% of the directionally selective cells showed spatial summation. About 32% had inhibitory mechanisms which decreased the response of the cell if the stimulus exceeded a maximum size. There was little or no evidence that LS area cells were orientation selective or sensitive to variations in stimulus shape independent of size.

Organization of cat striate cortex: a correlation of receptive-field properties with afferent and efferent connections.

Abstract: The purposes of this study were 1) to relate the receptive-field characteristics of area 17 cells to their afferent and efferent connections, and 2) to obtain quantitative data from area 17 neurons for later comparison with area 18 cells. Intra- and extracellular recordings were obtained in paralyzed preparations which were anesthetized with nitrous oxide. The connectivities of the recorded cells were determined from responses to electrical stimulation of afferent and efferent pathways. In parallel to the classification of units as simple and complex cells, the receptive fields were grouped in four classes according to the spatial arrangement of on- and off-areas; class I, fields with exclusive on- or off-areas; class II, fields with spatially separate on- and off-areas; class III, fields with mixed on-off areas; class IV, fields which could not be mapped with stationary stimuli. The results from electrical stimulation suggest two major classes of cells: cells in the first group are driven mainly or exclusively by LGN afferents. They rarely receive additional excitation from intrinsic or callosal afferents and rarely possess corticofugal axons. Cells in the second group receive either converging inputs from LGN afferents and further intrinsic afferents or only from intrinsic afferents. They frequently received additional input from callosum and from recurrent collaterals of corticofugal axons. They project subcortically more often than cells in the first group. Cells in both groups can be driven either by X- or Y-type afferents. Cells in the first group have mainly class I and class II fields or simple fields, whereas the neurons in the second group have mainly class III and class IV fields or complex fields. Thus, simple and complex cells differ in their connectivity patterns, but the discriminative parameter is neither the selective connection to the X- or the Y-system nor, in a strict sense, the synaptic distance from subcortical input. From the combined consideration of receptive-field properties and connectivity patterns it is concluded that class I and class II cells or simple cells are concerned mainly with the primary analysis of subcortical activity, whereas class III and class IV cells or complex cells perform a correlative analysis between highly convergent activity from extrinsic and intrinsic afferents.

Neuronal and glial activity during spreading depression in cerebral cortex of cat.

Abstract: 1. Extra- and intracellular potentials were recorded from neurons and glia during spreading depression (SD) in cerebral cortex of cats. The glial membrane depolarized during SD and the time course of depolarization was concurrent with the surface DC change of SD. The glial depolarization evoked by 20-Hz repetitive cortical stimulation disappeared during the negative DC shift of SD. Simultaneous recording of the extra- and intracellular potentials from a single glial cell with a coaxial microelectrode showed that the extracellular DC potential change was of opposite polarity to the glial intracellular potential, which suggests that the slow glial depolarization concurrent with SD is not the field potential. In contrast to glial cells, the neuronal burst discharges as well as the neuronal membrane depolarization associated with SD did not show a close relationship to SD: the neuronal membrane depolarization and discharge were frequently delayed by 10-3- s from the onset of the SD slow wave. Sometimes SD was observed without accompanying neuronal depolarization. The degree of neuronal depolarization was not always correlated with the amplitude of the negative wave of SD. 2. The effect of tetrodotoxin (TTX) on the negative DC potential of SD was examined. Simultaneous recording of glial membrane potential and the neuronal unit activity as well as extracellular DC potential and surface DC potential during SD was performed and the TTX-treated cortex was compared with the normal state. TTX did not change the DC level of the cerebral cortex. SD could be evoked by KCl when neuronal discharge was completely abolished by TTX application...

An olfactory projection area in orbitofrontal cortex of the monkey

Abstract: An olfactory projection area was studied in monkeys anesthetized with Nembutal. 1. Evoked potentials were recorded when the olfactory bulb (OB) was electrically stimulated in the lateroposterior portion of the orbitofrontal cortex (LPOF). However, those potentials disappeared when the anterior pyriform cortex (AP) (probably together with the medial portion of the amygdala (MA)) was aspirated or electrically destroyed. 2. In nearly the entire hypothalamic region, evoked potentials were recorded by the same stimulation of the OB. When the hypothalamic region was stimulated, evoked potentials were recorded in the LPOF. 3. The evoked potentials in the LPOF due to the OB stimulation never disappeared even when the thalamus was extensively aspirated or destroyed electrically, but they did disappear when the anterolateral and dorsoposterior portions of the hypothalamus were absorbed or electrocoagulated. 4. Evoked potentials in the mediodorsal nucleus (MD) of the thalamus were recorded when the OB was stimulated. When this nucleus was stimulated, evoked potentials were observed in the broad extent of the orbitofrontal cortex anterior to the LPOF, but never in the LPOF itself. 5. Monkeys were conditioned to discriminate two odors. When the LPOF was removed, such ability strikingly decreased; but when other areas in the prefrontal cortex were removed, the ability decreased only slightly. 6. It was concluded that there exists an olfactory pathway from the OB to the LPOF through the AP (and probably the MA) and the hypothalamus, but none through the thalamus, and that the LPOF plays an important role in the discrimination of odors. 7. It was proved that the entorhinal cortex (ER) is neither located as an intermediate olfactory area nor is it situated as a higher area than the LPOF in the newly found olfactory pathway stated above. It may be a link between the high olfactory area and the limbic system.

Somatotopic representation of hindlimb skin in cat dorsal horn.

Abstract: Single-unit exploration of the dorsal horn of segments L4-S2 of unanesthetized cats with the neuraxis transected at lower thoracic levels reveals a somototopic organization in the horizontal plane. The dorsal horn dermatomes correspond closely to the dermatomes of the corresponding dorsal roots, and the ML gradient is equally well described by two different projection schemes: a distoproximal gradient and a ventrodorsal one (5, 33). There is no evidence of segmental discontinuity of the map. As is the case in other nuclear regions of the CNS, the relative area devoted to projections from the foot is disproportionately large relative to the area devoted to skin regions of similar size which are located more proximally on the limb. From our data, and from the close correspondence to anatomical data obtained by others, we suggest that at least some cutaneous afferent fibers from a given skin area project directly to any dorsal horn region where that skin area is represented. This assumption, together with the organization of the dorsal horn map, yields a model which predicts a precise somatotopic organization of presynaptic neuropil in the substantia gelatinosa.

Morphology and enzyme histochemistry of dorsal muscles of the cat neck.

Abstract: An examination has been made of the five dorsal muscles of the cat neck which insert into the lamboidal crest. The three larger muscles, splenius, biventer cervicis, and complexus, are characterized by the presence of tendinous inscriptions which serve as the insertion points of shorter muscle fibers which do not run the length of the muscle. Longer fibers are bound by the inscriptions and, thus can transmit tension developed by shorter fibers. These three muscles are multiply innervater by nerves emerging from upper cervical spinal roots. Multiple innervation is not associated with multiple end plates but with arrangement so that lower roots innervate a high proportion of short fibers and higher roots, a high proportion of long fibers. Occipitoscapularis and rectus capitis major are, by comparison, simple muscles, each with a single motor nerve. Of the muscles examined, occipitoscapularis alone does not have its origin on the vertebral column but on the scapula, and is unlikely to have any major function in head movement.

Electrophysiological study of formation of new synapses and collateral sprouting in red nucleus neurons after partial denervation.

Abstract: Intracellular recording was made from cat's red nucleus after chronic lesion of the nucleus interpositus (IP) of the cerebellum and the properties of the corticorubral EPSPs were examined. 2. It was found that the time to peak of the corticorubral ESPSs induced from cerebral peduncle (CP EPSP) of chronic cats was much faster than that of normal cats. There was no simple decay following the rapid rise and early summit; instead there was another peak as if the slow normal CP EPSPs were superimposed on the fast ones. 3. By stimulating two loci, sensorimotor cortex and the cerebral peduncle, the conduction velocities of the fibers responsible for the newly appeared fast-rising component of the corticorubral EPSPs were measured. They were almost the same as those of normal corticorubral EPSPs.

Physiologic characteristics of vestibular first-order canal neurons in the cat. II. Response to constant angular acceleration.

Abstract: The physiologic response of first-order vestibular canal neurons, recorded within the internal auditory canal with glass microelectrodes, was studied in anesthetized cats. Neurons from all three canals were subjected to velocity trapezoidal rotations about the canal axis, and about different axes extending up to 90 degrees on either side of the canal axis in "roll" and 30 degrees on either side of "pitch." Each cell examined exhibited a spontaneous discharge and responded to constant angular acceleration in a fashion predictable from the direction of the in-plane acceleration vector and the known receptor hair cell polarization. Under conditions of prolonged constant acceleration, (5 degrees/s2 for 40 s) about 30% of the units which could be classified showed adaptation, 55% did not, and 14%, termed reverse adapting cells, demonstrated a fast rise followed by a slower, continual increase during stimulation. Secondary responses (undershoot or overshoot) were noted in most adapting neurons, but were absent in the reverse adapting group. Adapting neurons were distinguished from the nonadapting group by significantly lower resting rates, more irregular interspike-interval distributions, and greater sensitivity to acceleration. When compared with nonadapting neurons, reverse adapting cells had higher spontaneous rates, less irregular spike intervals, and higher sensitivities. The mean canal sensitivity to angular acceleration for all cells was 2 spikes . s-1/deg . s-2 (range 0.3-7.4 spikes . s-1/deg . s-2). Significant differences in mean sensitivity values between canal neurons were demonstrated, with those from the anterior being the most sensitive, followed by the posterior and horizontal canals, respectively. Time constants for all canals governing the transitory rise (or fall) in rate with constant acceleration averaged 3.8 s. Small differences in mean values were noted between canals but these were not significant. Incremental time constants were found to be slightly but significantly longer (mean = 3.9 s) than decremental time constants (mean = 3.6 s). Some cells showed different tine constants to many trials of one stimulus as well as to different levels of stimulus. Most canal unitary responses were approximately linearly related to stimulus magnitudes over the range of 2-18 degrees/s2. This being the case, the angle between the canal plane and plane of stimulus become the main determinant in the first-order neural response. Here, a linear cosine relationship descriged the three-dimentionsal unitary response curve: maximum canal response was elicited with rotation about the canal axis, while no response was evoked with rotation about an axis approximately 90 degrees to canal axis. Between these two extremes, the response of a cell was determined by the cosine of the angle between the canala axis and the axis of rotation.

Physiologic characteristics of vestibular first-order canal neurons in the cat. I. Response plane determination and resting discharge characteristics.

Abstract: The response plane and resting rate characteristics of first-order, vestibular, semicircular canal neurons were studied in 67 cats under sodium pentobarbital anesthesia using single-unit recording techniques in the eighth nerve. Five hundred fifty-nine units were classified as to the canal they were associated with by employing an identification technique based on physiologic response patterns to brief, high-level (up to 250 degrees/S2) angular accelerations delivered in various head positions. All horizontal canal neurons had increased firing rates to ampullopetal and all vertical canal units to ampullofugal endolymph flow. The average observed roll and pitch null points for each canal were used to determine the average sensitivity vectors for the right horizontal, anterior, and posterior canals. These sensitivity vectors were at a variance of 4.6-10.2 degrees from those predicted by anatomical measurements (3). The mean resting discharge characteristics of 318 first-order neurons was 36.0 spikes/s (range 0.50-114 spikes/s). No significant difference was noted between horizontal and anterior canal neurons on horizontal and anterior canal neurons on the basis of resting rate. The resting rate of the posterior canal neuron population was significantly lower. The regularity of the resting discharge varied in all three canals and the average coefficient of variation was 0.238 for the population, with a range of 0.298-1.030. The population distribution of all resting-rate statistical parameters appeared to be unimodal, indicating that first-order canal neurons may not be broken into discrete populations on the basis of resting-rate characteristics. Of 47 adequately examined first-order canal neurons, 25 demonstrated a repeatable and predictable alteration in their resting discharge as their position to gravity was reoriented. This alteration was usually nonadapting and varied in magnitude according to the degree of tilt and original starting position. Of 25 canal gravity units, 4 had nearby units from the same canal which were unresponsive to gravity, suggesting the effect was due to a limited distortion of the crista or cupula rather than an overall displacement of the cupula.

Directionally sensitive ganglion cells in the rabbit retina: specificity for stimulus direction, size, and speed.

Abstract: The receptive fields of directionally sensitive ganglion cells in the rabbit retina were analyzed. Several types of experiment showed that each point within the receptive field of the cell is inhibited by a fairly wide area of points around it, lying on each side of the preferred-null axis as well as along the preferred-null axis in the preferred direction. The excitatory or responsive receptive field of these cells has an inhibitory surround: this inhibitory surround appears to be simply an extension of the inhibition that occurs within the center of the receptive field. Points toward the edge of the responsive receptive field are inhibited from an area around them which extends into the center of the receptive field and also into the inhibitory surround. Directionally sensitive retinal ganglion cells respond to moving spots better than to moving bars. This is particularly true for objects moved perpendicularly to the preferred-null axis. In some cells a spot moved perpendicularly to the preferred-null axis will give a substantial response, whereas a bar moved in the same direction will give no response at all. This phenomenon can be explained by the inhibitory area which surrounds each point within the receptive field; since this inhibitory area is asymmetrical, it is also responsible for the cell's directional sensitivity. When two bars oriented perpendicular to the preferred null axis are flashed, one after the other, the response to the second bar is nearly always reduced by the presentation of the first bar. This is true for many temporal and spatial sequences corresponding to movement in the preferred direction, as well as those corresponding to movement in the null direction. However, there are temporal and spatial sequences, corresponding to movement in the preferred direction, for which the response to the second bar is unaffected by the presentation of the first bar. The time delay for this does not vary from cell to cell--it is always approximately 20 ms for on-off directionally sensitive cells and approximately 180 ms for on directionally sensitive cells. The spatial separation does vary from cell to cell, between 0.13 degrees and 1.2 degrees in 11 on-off directionally sensitive cells. This spatial separation, which gives linear summation of the response to two bars flashed 20 ms apart in the preferred direction, is correlated with the speed of movement which gives the best response for a bar moved through the receptive field in the preferred direction.

Visual receptive fields and their images in superior colliculus of the cat.

Abstract: 1. The receptive fields of collicular neurons in the cat, recorded in a single microelectrode penetration, were not centered on a point in visual space, but nested eccentrically with the smaller fields displaced toward the area centralis. The eccentric nesting was not eliminated by correcting the fields for the tangent screen distortion or by making penetrations normal to the collicular surface in coronal and parasagittal planes. These findings do not support the idea that collicular cells form topographically organized columns oriented normal to the collicular surface. 2. When the receptive fields were plotted in the visual coordinate system of the collicular map, the nesting became much more concentric, suggesting that the eccentric nesting of the receptive fields in visual space was largely a product of the retinotectal coordinate transformation. 3. The profile of a collicular receptive field, plotted in the collicular visual coordinate system is called the receptive-field image. Receptive-field images tended to have oval shapes with the long axis oriented mediolaterally. Clusters of receptive-field images, plotted for single penetrations, appeared similar wherever they occurred in the collicular map, suggesting that a common pattern of neural convergence determines the geometry of the receptive-field images in all parts of the colliculus. 4. The neural substrate of the receptive-field images was examined by tracing the theoretical patterns of neural activity which a point stimulus would produce in the retinotectal system. This analysis suggested that the shape and dimensions of the receptive-field images, and consequently the receptive fields, might be accounted for in large part by the geometry of collicular dendritic fields, the dimensions of the visual receptive fields of afferent fibers, and the retinotectal coordinate transformation. 5. Because it adjusts for the retinotectal distortion of visual space, the receptive-field image may be used to outline the distribution of collicular cells excited by a point stimulus. This makes it possible to show that a point stimulus activates large-field cells in the superficial gray layer over an area of about 2.5 by 1.5 mm in the central parts of the colliculus. It is suggested that such cells may organize the directional signals required by the oculomotor system for visual orienting behavior.

Projections of extraocular, neck muscle, and retinal afferents to superior colliculus in the cat: their connections to cells of origin of tectospinal tract.

Abstract: Unit recordings were made in the superior colliculus of cats anesthetized with chloralose and with Pentothal. Electrical stimulation of extraocular muscle afferents and neck muscle afferents excited more units in the superior colliculus than did a variety of moving and stationary visual stimuli. Units responding to neck muscle afferent stimulation fell into three populations; one population firing with a short latency and following stimulus presentation up to 1/s, a second population with a long latency and following stimulus presentation at frequencies lower than 15/min, and a third population exhibiting paired firing. The latencies and firing patterns of the third population combined the characteristics of each of the first two patterns. It is suggested that these characteristics of unit discharges stem from the existence of two pathways from neck muscle afferents to the superior colliculus. The projection is predominantly bilateral. Units responding to neck muscle afferent stimulation are distributed throughout the superior colliculus on the basis of their latencies. Long-latency responses predominate in the superficial layers of the superior colliculus and short-latency responses, while more common in the intermediate and deep layers, predominate in the tegmentum. Extraocular muscle afferent projections to the superior colliculus constitute the single richest projection found in these experiments. While the response patterns and latencies are similar to those of the neck muscle afferents, long-latency responses are the most common and dominate in all collicular regions. Few units in the tegmentum could be excited by extraocular muscle afferents. Both extraocular muscle and neck muscle afferents show considerable convergence with one another and with retinal afferents within the superior colliculus. Cells of origin of the tectospinal tract were identified within the superior colliculus and tegmentum by antidromic excitation from the upper cervical cord. These cells were distributed predominantly within the intermediate and deep layers of the superior colliculus, and sparsely in the superficial layers and tegmentum. Almost 50% of the cells of origin of the tectospinal tract receive a convergent input from extraocular muscle and neck muscle afferents and from the retina. About 30% of the cells were inexcitable to the stimuli employed in these experiments. The significance of these projections is discussed with respect to superior collicular function in the cat and i

Visual activation of neurons in inferotemporal cortex depends on striate cortex and forebrain commissures.

Abstract: Neurons in inferotemporal cortex respond only to visual stimuli and a majority have receptive fields that extend well into both visual half-fields. After bilateral removal of striate cortex, no inferotemporal neurons responded to visual stimuli. After unilateral removal of striate cortex, inferotemporal neurons in both hemispheres responded only to stimuli in the hemifield contralateral to the intact striate cortex. After section of the corpus callosum and anterior commissure, inferotemporal neurons in both hemispheres responded only to stimuli in the hemifield contralateral to the recording site. These results indicate that inferotemporal cortex visual information from striate cortex and that the pathway from striate cortex to the contralateral inferotemporal cortex includes the forebrain commissures. This same striate-temporal pathway is also necessary for normal discrimination learning. We suggest that the converging input onto single inferotemporal neurons from widely separated retinal areas may provide a mechanism for stimulus equivalence over different parts of the visual field, and it may be the absence of such a mechanism that contributes to the visual discrimination deficit that follows inferotemporal lesions.

Progressive changes in kitten striate cortex during monocular vision

Abstract: Following initial rearing in either total darkness or normal illumination, kittens at different ages were subjected to right-eye closure and various periods of vision through the left eye. After the period of monocular vision, single units in striate cortex were tested for visual responsiveness through each eye. A severe reduction in the proportion of units responsive to the deprived eye occurred over the first few days of monocular vision. Functional abnormalities were variably present after 1 day, marked after 2.5 and 3.5 days, and complete after 10 days. Monocular vision produced very much the same effect on ocular dominance of striate units, provided age and duration of suture were identical, regardless of whether kittens had received prior dark- or light-rearing.

Discharge of spindle afferents from jaw-closing muscles during chewing in alert monkeys.

Abstract: The discharge of muscle spindle afferents from monkey spindle afferents from monkey jaw-closing muscles was studied during mastication of natural foods by extracellular recording from the fibers or cell bodies of the tract and mesencephalic nucleus of the fifth nerve. In all, 39 muscle afferents were studied. The spindle associated with 18 of the afferents was positively identified by the afferent's response to gentle, localized palpation of either the temporalis or masseter muscle. Discharge patterns were observed during mastication, and in the majority of cases the qualitative passive response characteristics of the spindle afferent were determined. During steady chewing spindle afferent discharge typically paused briefly during the initial rapid upward part of the chewing cycle. Firing generally began as the jaw slowed its upward movement, and firing rates during the slow grinding portion of the upward movement were within the range of 50-80 spikes/s. All spindles exhibited a brisk discharge during the opening movement, typically within the range of 100-150 spikes/s. One-third of the spindle afferents exhibited a brief, high-frequency burst of firing at the very beginning of the opening movement, presumably as a result of stretch applied to a spindle just previously subjects to fusimotor excitation. Although the results of the study make it clear that spindles in jaw-closing muscles are coactived along with the extrafusal muscle fibers, the fusimotor bias does not seem capable of sustaining discharge in the face of rapid shortening of the muscle. Furthermore, the fact that discharge rate during opening, when the jaw-closing motoneurons are quiescent, is much higher than at any part of the closing cycle, when the motoneurons are active, suggests that the muscle spindles cannot provide the primary excitatory drive to the motoneurons.

Proportion of muscles spindles supplied by skeletofusimotor axons (beta-axons) in peroneus brevis muscle of the cat.

Abstract: Of 32 cat peroneus brevis spindles, 23 (72%) were found to be supplied by a least 1 skeletofusimotor or beta-axon. A motor axon was identified as skeletofusimotor when repetitive stimulation of it elicited both the contraction of extrafusal muscle fibers and as acceleration of the discharge of primary ending, which persisted after selective block of the neuromuscular junctions of extrafusal muscle fibers. The block was obtained by stimulating single axons at 400-500/s for a few seconds. Of 135 axons supplying extrafusal muscle fibers, 24 (18%) were shown to be beta-axons; 22 beta-axons had conduction velocities ranging from 45 to 75 m/s. All but three beta-axons increased the dynamic sensitivity of primary endings. Beta-innervated spindles may also be supplied by dynamic gamma-axons.