Convergence between projections from different thalamic nuclei to columns of the rat somatosensory cortex

Primuline fluorochrome retrograde transport technique was used to investigate sources of thalamocortical projections to a single rat somatosensory cortex column connected with the projection of the C₃ vibrissa. Labeled cells were identified in eight different thalamic nuclei: two specific, five nonspecific, and one association nucleus. Labeled neurons differed in the degree of stain accumulated as well as cell numbers and density of distribution from one nucleus to another, indicative of the different arborization patterns of their axons within the cortex. Highest numbers of heavily stained cells as well as highest density of distribution were observed in the ventral thalamic nucleus. The convergence seen between different thalamocortical inputs on to a single somatosensory cortex column explains the functional differences observed between neurons belonging to the same column and makes the formation of functionally distinct neuronal groupings appear possible on this structural basis.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 168–174, March–April, 1989.     

Localization of sources of thalamic inputs into the sensorimotor cortex in the rabbit using retrograde axonal transport technique

It was shown that the rabbit sensorimotor cortex received afferent fibers from neurons located in the specific, nonspecific, and association thalamic nuclei using the retrograde axonal transport technique. The distribution, dimensions, and shape of the somata of relay neurons spread through the thalamic nuclei were analyzed. The total number of neurons sending out thalamo-sensorimotor-cortical fibers was calculated and the coordinates of loci with the highest density of these cells in each thalamic nucleus were identified. Multipolar and stellate cells with somata measuring 12–20 µm and 10–15 µm in diameter, respectively, prevailed amongst relay neurons. Amongst the specific nuclei, the majority of afferent fibers are sent out by the ventrolateral, ventral anterior, and anterior ventral nuclei. A comparable number of afferent fibers are sent out by the mediodorsal and paracentral nuclei; these split up among the association nuclei and paracentral nuclei, respectively. It is suggested that afferents from many different groups of thalamic nuclei are essential for the sensorimotor cortex to participate in thalamocortical interaction.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 87–94, January–February, 1987.     

Connections between presumed diencephalic nuclei of the lizard limbic system using horseradish peroxidase axonal transport technique

Connections between the anterior thalamic and habenular nuclei were investigated in the lizard by administering horseradish peroxidase to these nuclei. They were shown to have overlapping locations of afferent sources, namely basotelencephalic structures, nuclei of anterior and hippocampal commissures, preoptic and lateral hypothalamic area, and superior raphe nucleus, as well as common projection zones, viz: the mamillary complex and the ventral tegmental area. Specific connections confined to individual nuclei were discovered, apart from those common to the nuclei: A reciprocal connection with the dorsolateral hypothalamic nucleus (for the anterior dorsolateral nucleus), a projection to the interpeduncular nucleus (for the habenular nucleus), and to the dorsal hypothalamic area (for the dorsomedial nucleus). No sources of afferent pathways to the anterior thalamic nuclei were found in the mamillary complex. All the thalamic nuclei studied, togetherwith their connections, are considered diencephalic relay links in pathways comparable with the dorsal (in the case of the habenular nuclei) and the ventral (with respect to the anterior thalamic nuclei) pathways of the mammalian limbic system.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 110–120, January–February, 1987.     

Reactions of neurons of the orbitofrontal cortex to stimulation of optic thalamic nuclei

The reactions of 288 neurons of the orbitofrontal cortex (OFC) to stimulation of the posteroventral (VP), ventral anterior (VA), and reticular (R) nuclei, as well as the median center (CM) of the thalamus, were investigated in acute experiments on cats. OFC neurons can be divided into four groups by their reactions to stimulation of thalamic nuclei: 1) those which respond with an increase in the frequency of the discharges to single and serial stimuli with a frequency of up to 20/sec; 2) those which respond doubtfully to single stimuli with a frequency of 4–12/sec; 3) those which respond with inhibition of the background impulses; 4) those which do not respond to stimulation of the nuclei. Stimulation of the thalamic nuclei evoked responses of OFC neurons with a large scatter of the latent period duration. The responses of neurons to stimulation of the VP (mean latent period 19.1±6.1 msec) had the shortest latent period (sometimes less than 3–4 msec). Reactions with a longer latent period developed upon stimulation of the VA (23.8±7.4 msec) and CM (42.8±12.8 msec). The uniqueness of the links of the OFC with the various optic thalamic nuclei is shown in an analysis of the material obtained and possible methods of the activation of the neurons of this region from thalamic structures are discussed.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 350–358, July–August, 1971.     

Dendritic action potentials of pyramidal tract neurons in the cat sensorimotor cortex

The intracellular activity of pyramidal tract neurons was studied during electrical stimulation of ventrolateral and ventroposterolateral thalamic nuclei in acute experiments on cats immobilized by myorelaxants. Somatic action potentials were observed and spontaneous spikes were also produced by single and rhythmic stimulation of the thalamic nuclei at the rate of 8–14 Hz, by iontophoretic application of strychnine, and by intracellular depolarizing current pulses. These potentials had a relatively low and variable amplitude of 5–60 mV and are presumed to be dendritic action potentials. It is postulated that these variable potentials arise in the dendrites of pyramidal neurons with multiple zones generating such activity. No interaction was observed where somatic and dendritic action potentials occur simultaneously. The possible functional role of dendritic action potentials is discussed.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 18, No. 4, pp. 435–443, July–August, 1986.     

Distribution of directionally selective neurons within the thalamic nuclei and striopallidal complex of the human brain

Spike activity was analyzed in the course of visual testing for directional sensitivity in 177 neuronal populations in different thalamic nuclei and the striopallidal complex in the brain of nine parkinsonian patients, diagnosed and treated using implanted intracerebral electrodes. Directionally selective neurons were discovered in the centrum medianum, the thalamic zona incerta and reticular nucleus, the caudate nucleus, and the central area of the globus pallidus. Proportions and distribution of neurons with different properties were investigated in the thalamic nuclei and striopallidal complex.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 652–660, September–October, 1989.     

Neuronal populations in the posterior group of thalamic nuclei projecting to the amygdala and auditory cortex in cats

Neuronal populations which are sources of fiber tracts to the amygdala and auditory cortexin the posterior group of thalamic nuclei and adjacent structures of the cat mesencephalon were studied by the retrograde axonal transport of horseradish peroxidase method. It was shown that the peripeduncular, suprageniculate, and subparafascicular nuclei form numerous projections to the amygdala. In all parts of the posterior group of thalamic nuclei, common zones of localization of sources of ascending pathways into the amygdala and auditory cortex were demonstrated. A powerful source of projections to the amygdala from the caudal part of the medial geniculate body was discovered.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 16, No. 2, pp. 213–224, March–April, 1984.     

Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

Role of the caudate nucleus in the development of evoked synchronized activity

Synchronized activity (spindles, augmentation response) evoked by stimulation of thalamic nonspecific, association, and specific nuclei was investigated in chronic experiments on 11 cats before and after successive destruction of the caudate nuclei. After destruction of the caudate nuclei the duration of spindle activity in the frontal cortex and subcortical formations (thalamic nuclei, globus pallidus, putamen) was reduced to only three or four oscillations. In the subcortical nuclei its amplitude fell significantly (by 50±10%); in the cortex the decrease in amplitude was smaller and in some cases was not significant. Different changes were observed in the amplitude of the augmentation response, depending on where it was recorded. In the subcortical formations it was considerably and persistently reduced (by 50±10%); in the cortex these changes were unstable in character. Unilateral destruction of the caudate nucleus inhibited synchronized activity evoked by stimulation of the thalamic nuclei on the side of the operation only. Destruction of the basal ganglia (caudate nucleus, globus pallidus, entopeduncular nucleus, and putamen) did not prevent the appearance of synchronized activity; just as after isolated destruction of the caudate nucleus, after this operation synchronized activity was simply reduced in duration and amplitude. It is suggested that the caudate nucleus exerts an ipsilateral facilitatory influence on the nonspecific system of the thalamus during the development of evoked synchronized activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 239–248, May–June, 1977.     

Corticofugal influences on the activity of vestibular nuclei units in the cat

Neuronal responses to stimulation of vestibular motor and orbital cerebral cortex were recorded by extracellular techniques in the lateral and medial vestibular nuclei of the bulbar complex during experiments on unanesthetized, immobilized cats. Both phasic and (mostly) tonic response of predominantly inhibitory type were observed. Horseradish peroxidase was injected into the aforementioned nuclei of the vestibular complex during the course of morphological experiments. Labeled neurons were found in the anterior supra- and ectosylvian cerebral gyri, the region of the cruciform sulcus, and that of the orbital cerebral cortex. Findings are discussed from the aspect of corticovestibular interaction.Ivano-Frankovsk Medical Institute, Soviet Ministry of Health. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 802–809, November–December, 1987.     

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.     

Properties of monosynaptic connections between callosal neurons and specific thalamic nuclei

A comparative analysis of monosynaptic afferent and efferent connections of callosal neurons and target neurons of transcallosal fibers with neurons of the specific ipsilateral thalamic nuclei (ventral posterolateral, ventral posteromedial, ventral lateral, and anteroventral) was undertaken on the sensomotor cortex of unanesthetized rabbits, using an electrophysiological method. Differences were demonstrated between callosal neurons and target neurons of transcallosal fibers with respect to monosynaptic inputs from the thalamic nuclei and pathways proceeding toward these structures and (or) entering the pyramidal tract. Among target neurons, compared with callosal neurons, more cells had descending projections (54 and 14%, respectively). Monosynaptic action potentials arose in 22% of target neurons in response to stimulation of specific thalamic nuclei, whereas no such responses occurred in callosal neurons. Projections of target neurons into thalamic nuclei were shown to be formed both by independent fibers and by axon collaterals of the pyramidal tract. It is postulated that the distinctive properties thus discovered indicate significantly greater convergence of influence of thalamic relay neurons on the target neurons; this determines differences known to exist in characteristics of receptive fields and spontaneous and evoked activity of callosal neurons, on the one hand, and of neurons excited synaptically by transcallosal stimulation, on the other hand.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 305–314, May–June, 1985.     

Analysis of long cortical evoked potentials

Evoked potentials arising in the motor cortex in response to its direct stimulation (dendritic and slow negative potentials), to stimulation of the ventrolateral (primary response) and intralaminar (nonspecific response) thalamic nuclei, and to stimulation of the pyramidal tracts (antidromic response), and also postsynaptic responses of neurons corresponding to them were studied in acute experiments on curarized cats. Evoked potentials arising in response to direct cortical stimulation and also to stimulation of the specific and nonspecific thalamic nuclei and pyramidal tracts were recorded from the same point of the motor cortex, and the corresponding intracellular responses were recorded from the same neuron. Slow negative potentials arising under these conditions of stimulation and the IPSPs corresponding to them were shown to have an identical time course. The results show that slow negative potentials are a reflection of hyperpolarization of pyramidal neurons. It is suggested that the individual components of responses evoked by direct stimulation of the cortex and thalamic nuclei have a common genesis.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 14, No. 2, pp. 115–121, March–April, 1982.     

Unit responses of the cat caudate nucleus to cortical stimulation before and after destruction of nonspecific thalamic nuclei

Responses of caudate neurons to stimulation of the anterior sigmoid and various parts of the suprasylvian gyrus were studied in acute experiments on cats. The experiments consisted of two series: on animals with an intact thalamus and on animals after preliminary destruction of the nonspecific thalamic nuclei. Stimulation of all cortical areas tested in intact animals evoked complex multicomponent responses in caudate neurons with (or without) initial excitation, followed by a phase of inhibition and late activation. The latent periods of the initial responses to stimulation of all parts of the cortex were long and averaged 14.5–25.5 msec. Quantitative and qualitative differences were established in responses of the caudate neurons to stimulation of different parts of the cortex. Considerable convergence of cortical influences on neurons of the caudate nucleus was found. After destruction of the nonspecific thalamic nuclei all components of the complex response of the caudate neurons to cortical stimulation were preserved, and only the time course of late activation was modified.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 464–471, September–October, 1980.     

Unit responses of the medial group of thalamic nuclei to stimulation of the frontobasal regions of the neocortex

In acute experiments on cats anesthetized with pentobarbital and chloralose, single-unit and focal responses of the medial group of thalamic nuclei (mediodorsal, central lateral, paracentral, central medianum, parafascicular) were studied to stimulation of the frontobasal regions of the cortex (proreal, posterior orbital, basal temporal regions). Depending on the number of neurons responding to cortical stimulation and on the length of the latent period of the responses three functionally heterogeneous subdividions of the medial nuclei were distinguished; the parvocellular and magnocellular portions of the mediodorsal nucleus and the intralaminar nuclei with the parafascicular complex. On the basis of responses of neurons activated antidromically by stimulation of the same cortical region and synaptically by stimulation of another region, the concept of the integrative function of nuclei of the medial group, integrating the frontobasal zones of the neocortex with the aid of neuron circuits in which the medial nuclei are included, is argued.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 9, No. 1, pp. 11–18, January–February, 1977.     

Thalamic inputs to the motor cortex studied in cats by retrograde axonal horseradish peroxidase transport

Thalamic afferent inputs of the motor cortex (area 4) were studied in cats by retrograde axonal transport of horseradish peroxidase (HRP). The main concentration of HRP-labeled neurons was found in rostral zones of the relay nuclei (of the ventrolateral and ventrobasal complex). A few labeled neurons were found in the mediodorsal association nucleus, where their distribution is quite local. HRP-labeled neurons of nonspecific intralaminar nuclei, projecting into the motor cortex, are present only in single numbers and show no tendency toward grouping in any parts of these nuclei. The results are evidence that the motor cortex receives heterogeneous afferentation from various thalamic nuclei, and it is evidently this which guarantees the reliability of transmission of incoming information.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 17, No. 2, pp. 250–255, March–April, 1985.     

Unit responses of the ventral posterior and ventral lateral thalamic nuclei to electrical stimulation of the thalamic reticular nucleus

A microelectrode investigation was made of responses of 72 physiologically identified neurons of the ventral posterior (VP) and 116 neurons of the ventral lateral (VL) thalamic nuclei to electrical stimulation of the reticular (R) thalamic nucleus. Mainly those neurons of VP and VL (73.7 and 86.2% respectively) which responded to stimulation of the first motor area and nucleus interpositus of the cerebellum responded to stimulation of R; 19.8% of VL neurons tested responded to stimulation of R by an antidromic action potential with latent period of 0.5–2.0 msec and 46.6% of neurons responded by orthodromic excitation; 23% of orthodromic responses had a latent period of 0.9–3.5 msec and 77% a latent period of 4.0–21.0 msec; 19.8% of VL neurons tested were inhibited. Among IPSPs recorded only one was monosynaptic (1.0 msec) and the rest polysynaptic. It is postulated that both R neurons are excitatory and that the inhibition which develops in VL neurons during stimulation of R are connected mainly with activation of inhibitory interneurons outside the reticular nucleus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 5, pp. 477–485, September–October, 1977.     

Response of recticular and dorsal thalamic nuclei neurons during extinction of conditioned implementation in the cat

Unit activity in 66 neurons of the reticular (R) nucleus and 31 neurons of the ventropostrolateral nuclei of the thalamus, and 14 neurons of the posterolateral nuclear complex, the pulvinar, were studied during extinction of the conditioned food implementation reflex. The number of R neurons that had responded to initial excitation in the first 300 msec after the conditional stimulus (CS) decreased with the extinction. Simultaneous disappearance of conditioned-reflex placement movements and late excitatory and inhibitory responses of R and dorsal thalamic nuclei neurons with latent periods exceeding 300 msec was also observed. Extinction of the conditioned reflex (CR) led to a significant lowering of background activity in two-thirds of investigated R and other thalamic nuclear neurons. This suggests that efferent effects from the reticular nucleus are decreased during Cr extinction.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 1, pp. 3–8, January–February, 1991.     

Involvement of thalamic neurons and the striopallidal complex in maintaining constancy of visual perception in the human brain

Neuronal activity was investigated in different thalamic nuclei and the striopallidal complex in parkinsonian patients with long-term implantation of intracerebral electrodes in the structures concerned for diagnostic and therapeutic purposes. Directionally selective neurons were found with consistent response to presentation of visual stimuli oriented at the same angle in a variety of (spatial) head positions differing by 90°.Institute of Experimental Medicine, Academy of Medical Sciences of the USSR, Leningrad. Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 93–101, January–February, 1989.     

Neural connections of the lizard septum investigated by HRP axonal transport techniques

Neuronal connections were investigated in the lizard (Ophisaurus apodus) by injecting horseradish peroxidase. Reciprocal connections were found between the septum and the dorsal and mediodorsal cortex, as well as projections from the diagonal bundle nucleus and the anterior dorsolateral and dorsomedial thalamic nuclei to the septum. The most clear-cut bilateral connections were observed between the septum and the preoptic region, the hypothalamic periventricular structures, and the lateral hypothalamic region (containing dopaminergic neurons) as well as nuclei of the mamillary body. Some characteristics and the overall organization pattern of connections between the septum and other limbic system structures are reviewed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 3, pp. 398–407, May–June, 1988.