Frequency analysis of motor responses evoked in unanesthetized cats by stimulation of the motor cortex

Frequency characteristics of motor responses evoked by stimulation of the motor cortex by amplitude- and frequency-modulated stimulus sequences were investigated in chronic experiments on unanesthetized cats. The variable component of evoked muscular contraction was studied. Frequency characteristic curves were plotted by the harmonic linearization method. Transformation of controlling signals in the motor system was shown to take place by low-frequency filtration and to be characterized by nonstationary, nonlinear, and frequency-dependent properties. Phase delay of the principal harmonic of the variable component of evoked muscular contraction was minimal at a frequency of 0.2 Hz and it varied in different experiments from 40 to 90°. The increase in the phase delay and decline of the amplitude-frequency characteristic curves were particularly marked if the frequency exceeded 1–2 Hz. The mean phase delay at a frequency of 5 Hz was about 108°; the mean slope of the amplitude characteristic curves in the 2–10 Hz region was –12 dB/decade. It is suggested that definite correlation between the dynamic properties of the motor system may be determined, in particular, by the adaptive properties of the spike discharge of neurons concerned in the transmission of motor command signals.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 571–579, November–December, 1980.     

Transformation of the afferent tactile signal into a motor command in the cat motor cortex

Activity of 112 neurons of the precruciate motor cortex in cats was studied during a forelimb placing reaction to tactile stimulation of its distal parts. The latent period of response of the limb to tactile stimulation was: for flexors of the elbow (biceps brachii) 30–40 msec, for the earliest reponses of cortical motor neurons about 20 msec. The biceps response was observed 5–10 msec after the end of stimulation of the cortex with a series of pulses lasting 25 msec. Two types of excitatory responses of the neurons were identified: responses of sensory type observed to each tactile stimulation of the limb and independent of the presence or absence of motion, and responses of motor type, which developed parallel with the motor response of the limb and were not observed in the absence of motion. The minimal latent period of the responses of motor type was equal to the latent period of the sensory responses to tactile stimulation (20±10 msec). Stimulation of the cortex through the recording microelectrode at the site of derivation of unit activity, which increased during active flexion of the forelimb at the elbow (11 stimuli at intervals of 2.5 msec, current not exceeding 25 µA), in 70% of cases evoked an electrical response in the flexor muscle of the elbow.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 115–123, March–April, 1977.     

Neuronal responses of the reticular and anterior ventral thalamic nuclei to stimulation of the thalamic ventrolateral nucleus and motor cortex

Responses of 137 neurons of the rostral pole of the reticular and anterior ventral thalamic nuclei to electrical stimulation of the ventrolateral nucleus and motor cortex were studied in 17 cats immobilized with D-tubocurarine. The number of neurons responding antidromically to stimulation of the ventrolateral nucleus was 10.5% of all cells tested (latent period of response 0.7–3.0 msec), whereas to stimulation of the motor cortex it was 11.0% (latent period of response 0.4–4.0 msec). Neurons with a dividing axon, one branch of which terminated in the thalamic ventrolateral nuclei, the other in the motor cortex, were found. Orthodromic excitation was observed in 78.9% of neurons tested during stimulation of the ventrolateral nucleus and in 52.5% of neurons during stimulation of the motor cortex. Altogether 55.6% of cells responded to stimulation of the ventrolateral nucleus with a discharge of 3 to 20 action potentials with a frequency of 130–350 Hz. Similar discharges in response to stimulation of the motor cortex were observed in 30.5% of neurons tested. An inhibitory response was recorded in only 6.8% of cells. Convergence of influences from the thalamic ventrolateral nucleus and motor cortex was observed in 55.7% of neurons. The corticofugal influence of the motor cortex on responses arising in these cells to testing stimulation of the ventrolateral nucleus could be either inhibitory or facilitatory.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 460–468, September–October, 1978.     

Multisensory convergence on neurons of the motor cortex in unanesthetized cats

Postsynaptic potentials (PSPs) of 83 neurons in the motor cortex of unanesthetized cats in response to electrodermal, photic, and acoustic stimulation were investigated by intra-and quasi-intracellular recording methods. Most cells responded to stimulation of at least one limb. About 60% of neurons of the posterior and over 75% of neurons of the anterior sigmoid gyrus responded to stimulation of two (or more) limbs. In 29 of 39 neurons of the anterior and 12 of 44 of the posterior sigmoid gyrus PSPs with a short (less than 50 msec) and stable latent period were evoked by flashes and clicks. On presentation of two somesthetic stimuli complete blocking (if the interval was less than 30–60 msec) or weakening (interval 30–200 msec) of responses to the second (testing) stimulus was observed. On presentation of paired photic (or acoustic) stimuli or paired stimuli of different modalities at various intervals from 0 to 100 msec, the testing response was often potentiated. The character of the responses and their interaction thus differed from those obtained under chloralose anesthesia [6, 7]. It is postulated that under the action of chloralose a system of neurons with strong excitatory feedback is formed in the motor cortex which may respond to stimuli of different modalities by something resembling the "all or nothing" principle.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 563–573, November–December, 1971.     

Spontaneous and evoked unit activity of the septum and hippocampus transplated into the rat neocortex

Embryonic septal and hippocampal tissue was transplanted into a cavity formed by removal of part of the parietal cortex of adult rats by suction. By extracellular recording 4–6 months after the operation cells with spontaneous activity with a frequency of 3.6±0.4 Hz, characterized by an irregular, stochastic spike distribution, were detected in the graft. About 90% of cells responded to electrical stimulation of neighboring cortical areas after a latent period of 5–43 msec. The most stable responses appeared to stimulation with frequencies of 5–10 Hz; in most cases the evoked discharge was followed by a period of inhibition of spontaneous activity (100–700 msec). The same number of cells responded to tactile stimulation of the body surface and vibrissae of the recipient animal. Specific responses of different types with latent periods of between 50 and 600 msec were observed. Normalization of unit activity of intracerebral grafts compared with activity of cells in tissue developing in the anterior chamber of the eye, and their functional integration with the recipient's brain are discussed.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 160–168, March–April, 1985.     

Neuronal and synaptic mechanisms of cortical inhibition

The latent periods, amplitude, and duration of IPSPs arising in neurons in different parts of the cat cortex in response to afferent stimuli, stimulation of thalamocortical fibers, and intracortical microstimulation are described. The duration of IPSPs evoked in cortical neurons in response to single afferent stimuli varied from 20 to 250 msec (most common frequency 30–60 msec). During intracortical microstimulation of the auditory cortex, IPSPs with a duration of 5–10 msec also appeared. Barbiturates and chloralose increased the duration of the IPSPs to 300–500 msec. The latent period of 73% of IPSPs arising in auditory cortical neurons in response to stimulation of thalamocortical fibers was 1.2 msec longer than the latent period of monosynaptic EPSPs evoked in the same way. It is concluded from these data that inhibition arising in most neurons of cortical projection areas as a result of the arrival of corresponding afferent impulsation is direct afferent inhibition involving the participation of cortical inhibitory interneurons. A mechanism of recurrent inhibition takes part in the development of inhibition in a certain proportion of neurons. IPSPs arise monosynaptically in 2% of cells. A study of responses of cortical neurons to intracortical microstimulation showed that synaptic delay of IPSPs in these cells is 0.3–0.4 msec. The length of axons of inhibitory neurons in layer IV of the auditory cortex reaches 1.5 mm. The velocity of spread of excitation along these axons is 1.6–2.8 msec (mean 2.2 msec).A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 394–403, May–June, 1984.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

Role of different types of fibers of the infraorbital nerve in synaptic activation of masseter and digastric motoneurons

Postsynaptic potentials of motoneurons of the masseter and digastric muscles evoked by stimulation of the infraorbital nerve with a strength of between 1 and 10 thresholds were investigated in cats anesthetized with a mixture of chloralose and pentobarbital. Depending on their ability to be activated by low-threshold afferents of this nerve, motoneurons of the masseter were divided into two groups. Stimuli with a strength of 1.2–2.5 times above threshold for the most excitable fibers of the infraorbital nerve evoked short-latency EPSPs in the motoneurons of the first group; a further increase in stimulus strength (3–9 thresholds) led to the appearance of IPSPs with latent periods of 2.8–3.5 msec. Motoneurons of the second group responded to stimulation of the infraorbital nerve with a strength of 3–9 thresholds by IPSPs whose latent periods varied from 6 to 8 msec. Stimuli below 3 thresholds in strength evoked no responses in these motoneurons. Stimulation of the infraorbital nerve with pulses of between 1 and 2 thresholds in strength evoked EPSPs in digastric motoneurons, but an increase in the strength of stimulation led to action potential generation. The presence of many excitatory and inhibitory inputs formed by afferent fibers of different types evidently provides a basis for functional diversity of jaw-opening and jaw-closing reflexes.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 6, pp. 596–603, November–December, 1980.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

Corticofugal influences on the motoneurons of the trigeminal nucleus

We studied the postsynaptic potentials evoked from 76 trigeminal motoneurons by stimulation of the motor (MI) and somatosensory (SI) cortex in the ipsilateral and contralateral hemispheres of the cat. Stimulation of these cortical regions evoked primarily inhibitory postsynaptic potentials (PSP) in the motoneuron of the masseter muscle, but we also observed excitatory PSP and mixed reactions of the EPSP/IPSP type. The average IPSP latent period for the motoneurons of the masseter on stimulation of the ipsilateral cortex was 6.1±0.3 msec, while that on stimulation of the contralateral cortex was 5.2±0.4 msec; the corresponding figures for the EPSP were 7.6±0.5 and 4.5±0.3 msec respectively. Corticofugal impulses evoked only EPSP and action potentials in the motoneurons of the digastric muscle (m. digastricus). The latent period of the EPSP was 7.6 msec when evoked by afferent impulses from the ipsilateral cortex and 5.4 msec when evoked by pulses from the contralateral cortex. The duration of the PSP ranged from 25 to 30 msec. Postsynaptic potentials developed in the motoneurons studied when the cortex was stimulated with a single stimulus. An increase in the number of stimuli in the series led to a rise in the PSP amplitude and a reduction in the latent periods. When the cortex was stimulated with a series of pulses (lasting 1.0 msec), the IPSP were prolonged by appearance of a late slow component. We have hypothesized that activation of the trigeminal motoneurons by corticofugal impulsation is effected through a polysynaptic pathway; each functional group of motoneurons is activated in the same manner by the ipsilateral and contralateral cortex. The excitation of the digastric motoneurons and inhibition of the masseter motoneurons indicates reciprocal cortical control of their activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 512–519, September–October, 1971.     

Neurophysiological evaluation of central-peripheral sensory and motor pudendal fibres

Extensive neurophysiological investigations were carried out in 18 healthy volunteer subjects, and 6 patients with neurological disease. The tests consisted of spinal and scalp somatosensory evoked potentials (SEPs) to stimulation of the dorsal nerve of penis/clitoris, motor evoked potentials (MEPs) from the bulbocavernosus muscle (BC) and anal sphincter (AS) in response to scalp and sacral root stimulation, and measurement of sacral reflex latency (SRL) from BC and AS.In the control subjects, the mean sensory total conduction time (sensory TCT), as measured at the peak of the scalp P40 wave was 40.9 msec (range: 37.8–44.2). The mean sensory central conduction time (sensory CCT = spine-to-scalp conduction time) was 27.0 msec (range: 23.5–30.4).Transcranial brain stimulation was performed by using a magnetic stimulator both at rest and during voluntary contraction of the examined muscle. Sacral root stimulation was performed at rest. Motor total conduction times (motor TCT) to BC and AS muscles were respectively 28.8 and 30.0 msec at rest, and 22.5 and 22.8 msec during contraction. Motor central conduction times (motor CCT) to sacral cord segments controlling BC and AS muscles were respectively 22.4 and 21.2 msec at rest, and 15.1 and 12.4 msec during contraction.The mean latencies of SRL were respectively 31.4 msec in the bulbocavernosus muscle and 35.9 msec in the anal sphincter. Combined or isolated abnormalities of SEPs, MEPs and SRL were found in a small group of patients with neurological disorders primarily or secondarily affecting the genito-urinary tract.     

Role of cortical inhibition in heterosensory interaction of neurons of the cat sensorimotor cortex

Background and evoked neuronal activity in the cat sensorimotor cortex was recorded under a-chloralose anesthesia. Pairs of heterogeneous stimuli were applied, spaced at intervals of 0, 100, 200, 300, and 400 msec. A clicking sound, flashing light, and electroshock to the contralateral forepaw were used as stimuli. Partial or complete blockade of response to test stimuli presentations spaced 100–200 msec apart were observed when using stimulation of varying modality. The greatest test response was recorded at interstimulus intervals of 200–300 msec. Intracellular mechanisms of heterosensory interaction were investigated by applying the inhibitory transmitter antagonist picrotoxin microiontophoretically to the test cell to produce local attenuation of inhibitory effects. This substance also reduced the duration of blockage following the conditioning stimulus and the occurrence of peak level test response at a lower interstimulus interval than in the controls. Either a consistent increase in the number of spikes per response at one of the interstimulus intervals or a uniform reinforcement in unit response to several different interstimulus intervals were observed in a proportion of the cells. The contribution of intracortical inhibitory influences to the mechanisms of heterosensory interaction on neurons of the cat sensorimotor cortex is discussed in the light of our findings.A. A. Ukhtomskii Institute of Physiology, A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 147–156, March–April, 1987.     

Activation of various areas of the ventral horn of lumbar segments during stimulation of the motor cortex

Focal potentials (FP) in segments L₆–L₇ of the ventral horn, evoked by stimulation of the motor cortex with series of stimuli of threshold magnitude for the flexor nerve response, were studied in acute experiments on cats. Appreciable differences were found to exist between the FP arising in the medial zone (layer VIII of Rexed) and those in the inner and outer parts of the lateral zone (layer IX). The FP of the medial zone appear earlier than in other zones (with a latency of 5–12 msec); they are multiphasic, negative components predominating over the positive ones. The FP from the inner part of layer IX possess the largest amplitude (up to 500 µV), a latency of 7–13 msec, a large first negative phase, and marked late positivity. Positive — negative FP (latency 9–15 msec) of small amplitude are recorded from the outermost portion of the ventral horn. The FP of the three zones mentioned above differ also with respect to other functional criteria. The FP of the medial zone are assumed to reflect the realization at the segmental level of the extrapyramidal component of descending cortical activity, the FP of both lateral zones reflecting reciprocal interrelations between postsynaptic processes in the motoneurons of flexor and extensor nuclei during implementation of a cortical motor reaction.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 175–184, March–April, 1971.     

Evoked potentials in the visual and association cortex of alert cats during paired uniform stimulation of the lateral geniculate body and pulvinar

Recovery curves of evoked potentials in the association and visual cortex during paired stimulation of the pulvinar in chronic experiments on alert cats were shown to be similar in character. Depression of the test response was observed only if the interval between stimuli was of the order of 10 msec, but if it was 40 msec considerable (2–4 times) facilitation of the second response was observed, mainly on account of an increase in the negative component N₁. Facilitation was less marked if the intervals were from 60 to 100 msec, and they decreased gradually to an interval of 200 msec. The recovery curve of cortical evoked potentials during paired stimulation of the lateral geniculate body differed considerably from the recovery curve during paired stimulation of the pulvinar and was characterized by a gradual increase in amplitude of the second response — from its almost total suppression with an interval of 10 msec to slight facilitation with an interval of 200 msec. If intervals of 10 to 80 msec were used, the test response was restored more slowly in the association cortex than in the visual cortex. The results are discussed from the standpoint of differences in the character of intracortical spread of excitation as a result of activation of geniculo-cortical and pulvinar-cortical pathways of conduction of information.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 497–505, July–August, 1984.     

Effect of response inhibition in cat motor cortex neurons during the expectation of conditioning stimulus

The spike responses of the motor cortex neurons (area 4) associated with forelimb movement were studied in awake cats earlier trained to perform placing motor reactions. Responses produced by the same neurons were compared in two situations: 1) when a sound-click conditioning stimulus (CS) was applied in isolation; 2) when a CS followed a preliminary warning stimulus (WS), a light flash, with a 100–1000 msec delay. During the reflex initiation by combined action of the WS and CS, response components that occurred prior to the placing movement (PM) performance under isolated CS action weakened and arrived 50–150 msec later; yet, response components that appeared in the same situation simultaneously with PM onset or later remained unchanged. PM latent periods were not changed when WS was applied. The temporal interval between WS and CS was characterized by depression of neuronal activity; depression duration was determined by the interstimulus delay. It is conceivable that the described transformations in spike responses of cortical neurons occurred due to changes in the sensory direction of the animal's attention; this direction, in all cases, is a crucial factor in the formation of neuronal activity in the cortex.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 21–27, January–February, 1993.t     

EPSPs of masseter motoneurons evoked by stimulation of low-threshold infraorbital nerve afferents in cat

Stimulation of the infraorbital nerve at strengths 1.4–2.5 times higer than the threshold of excitation of A fibers in cats anesthetized with chloralose and pentobarbital evoked EPSPs with an amplitude up to 3.0 mV and a duration of 9–15 msec in 69% of masseter motoneurons after 1.5–3.0 msec. These EPSPs were complex and formed by summation of simpler short-latency and long-latency EPSPs. The short-latency EPSPs appeared in response to infraorbital nerve stimulation at 1.1–1.5 thresholds and had a slow rate of rise (2.5–4.5 msec, mean 3.7±0.4 msec), low amplitude (under 2.0 mV), and short duration (5–6 msec). Their latent period varied from 1.5 to 3.0 msec (mean 2.1±0.2 msec). The shortness of the latent period and its constancy during stimulation of the nerve at increasing strength, and also the character of development of facilitation and inhibition of the EPSP during high-frequency stimulation suggests that these EPSPs are monosynaptic. The slow rate of rise suggested that these EPSPs arise on distal dendrites of the motoneurons. Long-latency EPSPs appeared 7–9 msec after stimulation of the infraorbital nerve at 1.1–1.5 thresholds. Their amplitude reached 1.5–2.0 mV and their duration 7–9 msec. The long duration of the latent period combined with low ability to reproduce high-frequency stimulation (up to 30/sec) points to the polysynaptic origin of these EPSPs.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 6, pp. 583–591, November–December, 1977.     

Disturbance and restoration of functions after division of spinal afferent pathways in the cat

The possibility and degree of recovery of motor and sensory functions in cats were studied after one-stage or two-stage bilateral division of the posterior columns and spinocervical tracts at the cervical level. Blocking the afferent inflow along these systems led to severe and prolonged disturbances of sensation and motor activity and was accompanied by a sharp decrease in nociceptive sensation. Weak (6–8 V) electrical stimulation of the skin of the limbs, which evoked a primary response of maximal amplitude in intact waking animals, evoked no electrical response in the somatosensory cortex of the chordotomized animals. However, on increasing the intensity of stimulation by 2, 3, or more times, low-amplitude negative waves with a spike latency of about 15 msec, together with slow late waves, were recorded in foci of maximal activity of the cortex. Recovery of motor activity and, to some extent, of proprioception was observed 2–4 months after injury; responses to tactile stimulation were not restored. In the course of compensatory reconstruction evoked activity in the somatosensory cortex did not recover. It is concluded that the recovery of motor activity in cats after injury to the afferent systems of the spinal cord can take place despite a considerable defect of somatic sensation.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 281–288, May–June, 1973.     

Corticofugal influences on postsynaptic processes in rubrospinal neurons in the cat brain

Composite and unitary EPSPs of red nucleus neurons evoked by stimulation of the sensomotor and association parietal cortex and nucleus interpositus of the cerebellum were studied in acute experiments on cats anesthetized with pentobarbital. A monosynaptic connection was shown to exist between not only the sensomotor, but also the association cortex, and rubrospinal neurons, in which unitary EPSPs appeared during stimulation of the association cortex after a latent period of 1.5–2.7 msec, with a peak rise time of 1.1–3.1 msec and an amplitude of 0.22–0.65 mV. Analysis of the temporal characteristics of the unitary EPSP suggested that synapses formed by fibers from the association cortex occupy a position nearer the soma than synapses formed by axons of sensomotor cortical cells.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 67–74, January–February, 1984.     

Responses of somatic cortical neurons during the conditioned placing reflex in cats

Unit activity was studied in areas 3 and 4 during the conditioned placing reflex in cats. Responses of somatic cortical neurons in this case were shown to develop comparatively late — 80–100 or, more often, 200–450 msec after the conditioned stimulus. In the motor cortex responses preceded movement by 50–550 msec, whereas in the somatosensory cortex they usually began simultaneously with or after the beginning of the movement. Judging from responses of somatic cortical neurons, the placing reflex is realized by the same neuronal mechanism as the corresponding voluntary movement. The differential stimulus and positive conditioned stimulus, after extinction of the conditioned placing reflex, evoked short-latency spike responses lasting 250–350 msec in the same neurons as took part in the reflex itself. In these types of internal inhibition, responses of the neurons were thus initially excitatory in character. Participation of the neurons in the conditioned placing reflex and its extinction, disinhibition, and differentiation, is the result of a change in the time course of excitatory processes and is evidently connected with differential changes in the efficiency of the various synaptic inputs of the neuron.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 392–401, July–August, 1982.     

Inhibition of jaw opening reflexes by stimulation of the central gray matter and raphe nuclei in cats

The effect of stimulation of the mesencephalic central gray matter and raphe nuclei on jaw opening reflexes evoked by excitation of high-threshold (dental pulp) and low-threshold (A-alpha) fibers of the infraorbital nerve afferents was studied in cats anesthetized with chloralose and pentobarbital. The jaw opening reflex evoked by stimulation of the dental pulp was shown to be effectively suppressed by conditioning stimulation of the central gray matter and raphe nuclei. The reflex evoked by stimulation of low-threshold infraorbital nerve afferents also was depressed (but less deeply and for a shorter period than the reflex evoked by stimulation of the dental pulp) during stimulation of the raphe nuclei and caudal zone of the central gray matter, but was unchanged after stimulation of the points located in the rostral zone of the central gray matter. Application of single stimuli or bursts of five stimuli with a frequency of 100 Hz had no effect on the reflexes studied. Short-term stimulation with a burst of 10–20 stimuli with a following frequency of 200–400 Hz led to inhibition of the reflexes, which lasted 450–1000 msec. Long-term stimulation of the central gray matter and raphe nuclei for 30 sec with a frequency of 50 Hz caused inhibition of jaw opening reflexes evoked by stimulation of both high- and low-threshold afferents for 60 min. Impulses from the central gray matter and raphe nuclei thus have a mainly inhibitory action on the jaw opening reflex evoked by stimulation of high-threshold afferents, but they act less effectively on the reflex evoked by stimulation of low-thres-hold afferents. The duration of inhibition depends essentially on the parameters of stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 3, pp. 374–387, May–June, 1984.