Neurons of the cat sensorimotor cortex: Responses related to differentiation of monomodal and heteromodal conditioning signals

Spike responses of the sensorimotor cortex neurons were studied in chronic experiments on cats trained to perform an operant reflex, a placing movement triggered by application of the distant stimuli. The responses recorded under conditions of differentiation of sound tones of various frequencies and of a heteromodal complex (light + tone) from its components were compared. The responses recorded from 125 neurons in 3 animals were analyzed. No neurons selectively responding either to monomodal or to heteromodal signals were found. Forty-five cells responded to positive signals by excitation or inhibition, irrespective of the signal modality. The shortest latencies of these responses were 30 and 40 msec, respectively. When inhibitory stimuli were applied, these neurons either generated much weaker responses, or did not respond at all. A correlation was found between the level of response depression and the level of differentiation of the signals by an animal. These findings allow us to hypothesize that the sensorimotor cortex does participate in differentiation of sensory signals, providing preparation for switching on the motor response after a positive stimulus or suppression of such a response after a negative one.Neirofiziologiya/Neurophysiology, Vol. 26, No. 4, pp. 251–261, July–August, 1994.     

Functional characteristics of visual cortical neurons of the cat

The characteristics of neurons in Area 17 of the visual cortex in cats were investigated by extracellular recording of their activity. Unit responses to flashes modulated by intensity and duration (100 µsec-1 sec) were recorded. Of 80 neurons tested, 67.6% were spontaneously active and 32.4% were silent. The threshold responses of the neurons to flashes varied by 7 logarithmic units. The distribution curve of the cells by response thresholds had one maximum corresponding to an energy of the order of 1–10 lm·sec. The time during which the cells could summate excitation did not exceed a mean value of 34 msec. Depending on the latent periods of the visual cortical neurons they can be divided into three groups. The first group includes neurons responding 20–40 msec after stimulation, the second and third neurons responding after 100–120 and 160–180 msec, respectively. Photic stimulation considerably altered the ratio between the numbers of cells generating spikes with high and low frequency. No correlation was found between the sensitivity of the visual cortical cells to light, the latent period of their response, and the critical time of summation. This shows that the cortex contains many duplicate units which are grouped together on the basis of only one of the functional characteristics of their spike response.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 2, pp. 173–179, March–April, 1970.     

Variations in neuronal responses of cat corticocerebral neurons to somatic stimulation on action of additional stimuli

Using alert cats we have investigated the impulse reactions (IR) of corticocerebral neurons (areas 3, 4, 5) in response to electrical stimulation of the contralateral limb (ESL). The short-latency impulse reactions of neurons of an excitatory nature, which were recorded in the animals in the state of rest, decreased considerably in intensity or could not be detected at all after preliminary (after 1.0–1.5 sec) action of a light flash or sound stimulation during the initial periods of their application. When the animals showed a defense or food motivation we observed, apart from a change in the background activity, evoked by the action of the ESL, more complex rearrangements of the impulse reaction, up to the appearance of the periods of inhibition of the impulse activity. Conversely, combined application of ESL with a stimulus of the same modality, did not prevent development of the initially isolated reaction even in cases of decrease in the ESL to a subthreshold value. A subthreshold stimulus "intensified" in this way can become important for the animal and be used as a signal stimulus during the development of the conditioned defense reflex in the animal. We assume that the nature of the reactions of the same neurons to a simple somatic stimulation is not constant. This is due to a preliminary tuning of the analyzers of the animal to the perception of stimuli of a certain modality.A. A. Bogomolets Institute of Physiology, Ukrainian Academy of Sciences, Kiev. Translated from Neirofiziologiya, Vol. 24, No. 1, pp. 27–37, January–February, 1992.     

Involvement of visual specific and association cortex input in the shaping of neostriatal neuron response to visual stimulation in unanesthetized cats

During chronic experiments on unanesthetized cats neuronal response in the caudate nucleus to the presentation of local photic stimuli and electrical stimulation of the specific (field 17) and the association (Clare-Bishop) areas were compared. Stimulation of the Clare-Bishop area proved more effective than stimulating field 17 for neurons of the caudate nucleus; a response was produced in 47% of test neurons in comparison with 8% of units only in the specific area. Lower average values were observed for latency of neuronal response to stimulation of the Clare-Bishop area. An insignificant number of caudate nucleus neurons were activated as a result of stimulation of both cortical areas. A comparison between the response of one set of neurons to electrical cortical and visual stimulation showed that cells responding to visual stimulation were more highly activated by stimulating the Clare-Bishop area than by stimulation of field 17. This type of neuron predominated in the caudate nucleus. A discussion follows of the possible involvement of the Clare-Bishop area in shaping neuronal response to visual stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 619–627, September–October, 1985.     

Inhibitory influence of supplementary extraneous stimulation upon neuronal responses in the sensorimotor cortex of the cat during a conditioned reflex

Using alert rabbits trained to perform placing movements in response to a sound click, we investigated impulse responses (IR) of neurons of the somatosensory cortex preceding realization of the reflex by 50–150 msec. When a brief extraneous stimulation (light flashes, audible tone, electrical stimulation of a limb) was applied after initiation of the reflex, learned movements with the earlier behavioral parameters (latent periods and duration) were maintained. However, the IR of neurons to the presentation of a conditioned stimulus (CS) was of lesser intensity and arose 50–250 msec later. A constant extraneous stimulation (an audible tone, a forced stream of air upon the muzzle) or a decrease in the intensity of the CS administered to the threshold of hearing resulted in similar changes in the neuronal responses upon the application of the CS, but the parameters of the learned movements were maintained. We suggest that the cause of these changes in neuronal responses is increased exteroceptive attention to extraneous stimulation to additional extraneous stimulation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 174–181, March–April, 1991.     

Effects of serotonin on neuronal response induced in the sensorimotor cortex by tactile and conditioned acoustic stimuli

Neuronal firing response in the sensorimotor cortex to tactile (non-conditioned) and acoustic (conditioned) stimuli was investigated in trained cats before and after iontophoretic application of serotonin and lysergide. Three functionally distinct groups of neurons were identified from the response produced by presenting tactile and acoustic stimuli. Applying serotonin was found to facilitate preliminary and residual spike response induced by tactile stimulation; it also facilitates and modulates response in many cortical neurons to conditioned stimuli. Facilitation takes the form of reduced latency of response and increased numbers of spikes in response to conditioned stimulus presentation, especially at the initial phase of response to sound and immediately after the onset of conditioned reflex motion. Additional neurons formerly unresponsive to acoustic stimuli joined in the reaction under the effects of serotonin. Changed response patterns often evolve following minor fluctuations in background activity level. It is suggested that facilitation of response following iontophoretic serotonin application in the neocortex is associated with activation of excitatory serotonin receptors (S₂). The lysergide-induced increase in background and evoked activity noted during experimentation can apparently be put down to blockade of inhibitory serotonon (S_1B) receptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 3, pp. 337–347, May–June, 1990.     

Neuronal responses in the limbic cortex of awake cats during defensive conditioning

Spike activity was investigated in limbic cortex neurons during defensive conditioning to acoustic stimulation in chronic experiments on cats. A relationship was found between the numbers of neurons responding, their contribution to formation of a temporal connection, and the duration of the acoustic stimulus. Phasic responses of 50–500 msec duration with latencies of 15–50 msec were observed for the most part. Intensive spike response with a minimum latency of 15 msec and a duration of between 200 msec and 2.5 sec evolved in most cells (95.1% in field 24 and 83% in field 32) in response to electrical stimulation. Response to acoustic stimulation rose during defensive conditioning in 33.3% cells and declined and finally disappeared in 13.3%, but response at the site where reinforcement was abolished was reproduced in all these cells. It was thus found that the numbers of limbic cortex neurons responding to sound not only fails to increase but actually decreases after training. The limbic cortex is thought to play its most active part in conditioning response to a recognized signal during the period preceding the awaited painful reinforcement.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 660–669, September–October, 1986.     

Involvement of mesencephalic reticular formation neurons in cat conditioned reflexes

Traditional defensive and operant food reflexes were used to investigate neuronal responses of the mesencephalic reticular formation. It was found that these neurons may be divided into different groups according to function, depending on how they respond to positive conditioning stimuli. Of the two main groups of neurons with sustained tonic reactions one is activated in response to positive acoustic conditioning stimulation; it no longer reacts to the same stimulus after extinction of the reflex, while the other only becomes involved in response to positive stimulation accompanying the initiation of movement. Neurons belonging to the second group begin to respond directly to acoustic stimulation after extinction of the conditioned reflex. Neurons of the mesencephalic reticular formation can thus exercise additional tonic ascending effects both in the production and inner inhibition of the conditioned reflex. The group of neurons with a phasic reaction, i.e., a double response (a direct response to sound and another produced by movement) displayed a drop in spontaneous activity during the shaping of inhibition of differentiation and of extinction in particular. It was found that the initial changes in the spike response of reticular formation neurons during conditioning and pseudo-conditioning are similar. There are thus grounds for stating that neurons of the mesencephalic reticular formation participate in the shaping, production, and inner inhibition of traditional and operant conditioned reflexes in a differentiated capacity rather than as a population reacting identically.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 161–171, March–April, 1986.     

Participation of midbrain periaqueductal gray matter in defense conditioning in rats

Responses of neurons of the periaqueductal gray matter (PAG) were studied in chronic experiments on cats during formation and extinction of a defensive conditioned reflex to sound and its differential inhibition. In response to conditioned stimulation these neurons developed phasic-tonic spike responses up to 3 sec in duration. During combination of stimuli these responses were formed long before the conditioned reflex and disappeared long after the latter was extinguished. In the case of an established conditioned reflex, the onset of spike responses occurred 100–200 msec before the appearance of motor responses. An increase in spike activity of tonic character in neurons of PAG preceded voluntary movements by 100–500 msec. The responses of these neurons to presentation of a differential stimulus consisted of groups of spikes 150–200 msec in duration. They were formed with difficulty, and their manifestation was made even more difficult by an interruption during the experiment and by preceding positive stimuli. On the basis of the results a conditioned reflex can be regarded as the result of a multilevel hierarchic process of readjustment of unit activity, which begins in the nonspecific structures of the midbrain.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 15, No. 3, pp. 278–287, May–June, 1983.     

Conduction of excitation in the cat visual system

Unit responses in area 17 of the visual cortex to stimulation of the lateral geniculate body and optic tract were studied in experiments on unanesthetized cats immobilized with D-tubocurarine. Of the neurons tested, 53.6% responded to stimulation of the lateral geniculate body. In 92% of these cells the responses were orthodromic with latent periods of between 2 and 12.5 msec. Most cells responded with latent periods of 2.0–2.5, 3.0–3.5, and 4.0–4.5 msec, corresponding to latent periods of the components of the electropositive wave of the primary response. Antidromic responses to stimulation of the lateral geniculate body were given by 8% of neurons. The difference between the latent periods of responses of the same visual cortical neurons to stimulation of the optic tract and lateral geniculate body was 0.1–1.8 msec, but for most neurons (55.8%) it was 0.5–1 msec. The histograms of response latencies of visual cortical neurons to stimulation of the above-mentioned formations were found to be similar. It is concluded that the optic radiation contains three principal groups of fibers with conduction velocities of 28.5–16.6, 11.7–8.9, and 7.4–6.0 m/sec, respectively.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 7, No. 6, pp. 589–596, November–December, 1975.     

Dynamics of the activity of rabbit visual cortex neurons during elaboration of elementary conditioned reflexes to time and association

Elaboration of a reflex to time (with omissions of stimuli) and of association; light--light + electrocutaneous stimulation of the paw was studied on neurones of the rabbit visual cortex. It was shown that by similarity of patterns of the discharge to a conditioned stimulus and to reinforcement, 83% of neurones reveal the formation of a reflex to time, and 57%--elaboration of association. Three ways of coding plastic reorganizations of the neuronal discharges are suggested; by the total number of spikes in the response, by the total sum of inhibitory periods, and by the pattern of the response. It has been found that in the reflex to time the early components of the response to the stimulus are reproduced during omissions; in elaboration of the association the late components of the discharge reaction to reinforcement are mainly repeated. Most cells with plastic reorganizations possessed polysensority and revealed discharge sensitization during habituation.     

Effects of local adaptation of receptive field on sensitivity of the cat visual cortex neurons to cruciform images

The responses to flashing single light bars of different orientation and to cruciform images (CI) were compared in 9 neurons of the cat striate cortex possessing high specific sensitivity to CI, during local adaptation of various receptive field (RF) zones. In most neurons, a two- to threefold reduction in the response to CI with a constantly present bar of optimum or orthogonal orientation, if compared with a response to the figure consisting of two flashing bars, was found. Responses to the CI including an adaptation bar were often increased, if compared with those observed at usual orientation tuning. The role of a cross-orientation inhibition in the formation of a selective sensitivity to CI in the neurons of the visual cortex is discussed.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 134–139, March–April, 1995.     

Neuronal spike response produced in the feline thalamic reticular nucleus by instrumental conditioned reflex

Spike response was investigated in 156 units of the thalamic reticular nucleus (RN) during performance of the instrumental feeding reflex of lever-pressing. This response consisted of lead and lag phases. Latency of the lead phase of response varied between 10 and 100 msec and total duration of response between 50 and 250 msec; minimum latency of the lag phase: 100–300 msec. Initial response to a conditioning clicking sound was found in 27 units, of which 26 showed excitation and the remaining single unit an inhibitory-excitatory pattern. The lag stage of response associated with performance of conditioned lever-pressing was found in 134 neurons, of which 115 showed an excitatory pattern, 19 displayed inhibition and the remaining 22 units failed to respond. The lag phase of response preceded the onset of conditioned reflex movement (CRM) in 30 neurons. A total of 118 neurons responded between the onset of CRM and the point of lever-pressing. It was concluded that the RN plays a part in perception of the conditioned signal as well as producing and controlling performance of CRM.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 8–18, January–February, 1991.     

Temporal summation in cat visual cortical neurons

Characteristics of temporal summation in neurons of area 17 of the visual cortex in acute experiments on unanesthetized, immobilized cats. During light adaptation, extracellular spike responses of these neurons to optimal local photic stimuli of varied duration — from 5 to 1000 msec — were studied. The critical duration of temporal summation of excitation, determined by the supraliminal method using the criterion of maximal discharge frequency in the first volley of the spike response, varied in different cells from 5 to 100 msec; neurons with summation lasting 15–100 msec (mean 31.45±5.67 msec) were found most frequently. Neurons with central receptive fields differed significantly from cellswith peripheral fields in the shorter critical duration of temporal summation, the lower frequency of spontaneous discharges, and the shorter duration of the first volley of the response. Summation time in neurons with simple receptive fields was significantly shorter than in neurons with complex receptive fields. The results of these experiments are compared with data in the literature obtained by the study of retinal and lateral geniculate neurons in cats and are discussed from the stand-point of division of ascending afferent projections in the visual system into X-and Y-groups (Ia and Ib).Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 13, No. 4, pp. 345–352, July–August, 1981.     

Response of parietal association cortex neurons to acoustic stimulation before and after auditory cortex blockage in the cat

The effect of auditory cortex blockade on response patterns of parietal association cortex neurons responding to different frequency tones was investigated in the cat. Blockade was produced by two methods: bilateral isolation and application of a 6% Nembutal solution to the auditory cortex surface. Frequency threshold curves were plotted for all test neurons. The majority of test neurons (84%) displayed one or two characteristic frequencies before blockade, as against only 63% of all neurons responding following blockade. Changes also affect the range of frequencies at which the cells could respond. Virtually all test neurons responded to application of a broad spectrum of frequencies under normal conditions. After blockade of the auditory cortex 69% of neurons no longer responded to tones above 8–10 kHz. This would suggest that mainly information on high frequency tones is transmitted via the auditory cortex. The question of where acoustic information for parietal association cortex neurons mostly originates is also discussed; association thalamic nuclei are thought to be the main source.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 354–360, May–June, 1986.     

Investigation of habituation reaction of neurons of the cat motor cortex

The neuronal and total surface activity of the cortical representation of the motor analyzer in the region of the posterior sigmoid gyrus of the cat brain in response to rhythmical light, sound, and electrical stimuli and their complexes was analyzed. Two groups of neurons were found, of which the first is characterized by a gradual decrease in the number of peaks in the response and by their subsequent disappearance and the second by the absence of a discharge in response to stimulation and by its development before the application of the next stimulus. The first group was comprised of neurons which do not have background activity and the second was made up of neurons with a background activity of 0.4–3.7 imp/sec. This reorganization of the activity of cortical neurons in response to rhythmical stimulation is considered to be a habituation phenomenon.A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 245–251, May–June, 1971.     

Dynamics of orientational tuning of feling visual cortex neurons under the effects of sombrevine

Dynamics of orientational tuning in 59 primary visual cortex neurons were investigated before and after sombrevine-induced anesthesia during acute experiments on immobilized cats using temporal slice techniques. A dynamic shift in preferred orientation of a flashing light strip, during which peak amplitude of spike discharges was noted (at an angle of between 22 and 157°) occurred as response developed in two-thirds of the cells. We had previously named this effect "scanning the orientational range" [9]. Scanning declined significantly in 45% of the sample, culminating in complete disappearance of this effect in some cells following sombrevine action. Scanning intensified in 30%, while dynamics of tuning remained unchanged in 25% of units. Sombrevine administration induced change in the preferred stimulus orientation of 60% of the neurons (referred to as "unstable" cells) and remained constant in "stable" cells (= 40%). Dynamic changes in preferred stimulus orientation were 2.5 times as high as those of stable cells in the waking state. The scanning effect declined significantly in 60% of "unstable" neurons under the action of anesthesia and remained unchanged in not more than 6%. At the same time, orientational tuning did not alter in the "stable" cell group in 46% of units, either declining (25%) or increasing (29%) in the remaining scanning ranges.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 107–113, January–February, 1990.     

Convergence of signals of various sensory modalities on the neurons of the sensorimotor zone of the rabbit cerebral cortex

The responses of the neurons to electrocutaneous stimulation, light flashes, and clicks in the cortical region of the motor representation of the rabbit forelimb were investigated by means of intra- and quasiintracellular recordings. In unanesthetized animals, in only eight out of 65 neurons did postsynaptic potentials (PSP) with a short (10–30 msec) latent period arise in response to light and sound. In 15 neurons, long latency (50–150 msec) responses to one or both of these stimuli were recorded. In most of the cells, short latency stable responses to stimulation of the contralateral forelimb and unstable long latency responses to light and/or sound, frequently of the nature of an increase in the background "synaptic noise," were observed. Under deep chloralose narcosis, the type of convergence was sharply changed: in most of the neurons, short latency responses to all the stimuli used appeared. However, the picture of convergence differed from that described earlier [5,6] for the motor cortex of the cat under chloralose narcosis. The responses to various stimuli were less similar to one another; the somesthetic modality substantially "predominated" (judging by the stability and nature of the interaction of the response).Brain Institute, Academy of Medical Sciences of the USSR. Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 5, pp. 474–483, September–October, 1971.     

Dynamics of single unit activity in the association cortex of waking cats during defensive conditioning

Responses of neurons in association area 5 during defensive conditioning to acoustic stimulation were studied in chronic experiments on cats. As a rule the neurons responded by excitation to presentation of conditioned and unconditioned stimuli. During the conditioned reflex unit responses usually appeared in the first 50 msec after the beginning of acoustic stimulation, i.e., they were connected with the action of the conditioned stimulus and not with manifestations of conditioned-reflex motion. The most significant changes in responses of cortical association units were observed in the initial period of conditioning. During stabilization of the conditioned reflex, responses of some neurons became stabilized, whereas in other neurons the spontaneous activity and intensity of responses increased, and in a third group the response to one of the stimuli disappeared. This last result indicates a switch during conditioning from polysensory unit responses to monosensory specialized responses. Extinctive inhibition was found to consist of a gradual decrease in the level of the spike discharge and its approximation to spontaneous activity, i.e., to be passive in character.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 563–572, November–December, 1978.     

Neuronal responses in the cat substantia innominata during instrumental conditioned reflex

Neuronal spike activity in the substantia innominata was investigated when establishing the instrumental conditioned reflex of lever-pressing with food reinforcement during chronic experiments on cats. Spike activity changed in 44.3% of neurons during this process; 24.3% responded directly to conditioned acoustic stimulation. Reactions associated with conditioned reflex movement were less pronounced. Response of peak intensity and duration was observed during food reinforcement, when the reaction occasionally occurred 500 msec in advance of the reinforcement provided. Involvement of cholinergic substantia innominata neurons in reinforcement is thought to be responsible for the persistence of residual effects in neocortical neurons.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 796–804, November–December, 1989.