Activity of the parietal associative cortex neurons and aminergic brainstem neurons at the performance of a voluntary movement in cats

Activity of 98 neurons of the parietal associative cortex (PAC) and 189 supposedly aminergic brainstem neurons (dopaminergic in thesubstantia nigra pans compacta, noradrenergic in thelocus coeruleus region, and serotonergic in theraphe nuclei) was recorded in awake cats. The animals were trained to perform a voluntary movement (pressing a pedal) not earlier than at a certain prefixed time moment. More than half of the recorded units modified their activity before the movement initiation. The PAC neurons responded mostly within the interval of planning of the movement, while reactions of aminergic neurons were observed in the course of its initiation, which probably provides facilitation of the responses of cortical neurons. The pattern of responses was rather specific for each of the studied neuronal populations.     

Origin of associative evoked potential of the orbital cortex

In acute experiments on cats evoked potentials (EP) of the orbital cortex were recorded and the electrogenesis and functional purpose of individual components of associative responses (AR) were investigated. It was concluded that the initial negative fluctuation of the AR arises as a consequence of the physical propagation of potentials from the projection somatosensory cortex and the second, positive, component and the following negative component are the result of arrival of an afferent volley into the orbital cortex via specific thalamic nuclei. These two components are due to activation of neurons of the orbital cortex. The afterdischarge, which appears sometimes, develops under the effect of impulses arriving from nonspecific thalamic nuclei. It is shown that during the second, positive, phase of the AR, primarily afferent neurons are activated, and during the negative phase, efferent neurons of the orbital cortex. The afterdischarge, which complicates the negative phase of the AR, is due to inhibition of afferent neurons.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 384–390, July–August, 1970.     

Unit responses of the cat parietal association cortex to stimulation of reticular and anteroventral thalamic nuclei

Responses of 124 neurons in the anterior division of the middle suprasylvian gyrus to stimulation of the reticular (R) and anteroventral (VA) nuclei and the pulvinar (Pulv.) of the thalamus were studied in acute experiments on unanesthetized cats immobilized with D-tubocurarine. Responses of 70 neurons to stimulation of R and Pulv. were investigated. Altogether 51.5% of the cells of this group responded to stimulation of R while 38.6% of neurons responded to stimulation both of R and of Pulv., indicating convergence of afferents from nonspecific and associative nuclei of the thalamus on these neurons. Responses of 54 cells to stimulation of VA and Pulv. were investigated. The tests showed that 72.2% of neurons responded to stimulation of VA and convergence of afferents from VA and Pulv. was found in 29.6% of neurons. As a rule neurons were excited in response to stimulation of R and VA. Inhibition was observed in only one neuron in response to stimulation of R and in six neurons in response to stimulation of VA. The latent period of responses to stimulation of R varied between 2.2 and 37.0 msec, of VA from 6.0 to 35.5 msec, and of Pulv. from 2.1 to 35.0 msec. The length of the latent periods to stimulation of nonspecific and associative nuclei were compared for groups of neurons for which convergence of afferent influences from R and Pulv. or from VA and Pulv. was found. The question of connections of R and VA with the parietal association cortex is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 339–347, July–August, 1973.     

Neuronal responses of the rate somatosensory cortex transplanted into the vibrissae representation field of the neocortex to the electrical stimulation of the recipient brain

Neuronal responses of the rat somatosensory cortex grafted into damaged host barrel field to electrical stimulation of the host brain were investigated extracellularly in rats under light pentobarbital anaesthesia. The following structures of the host brain were stimulated: ventrobasal complex and posterior thalamic nuclei, ipsilateral area of vibrissae representation in the sensorimotor cortex and contralateral barrel field. Reactivity of the grafted neurones was lower, than in the intact barrel field, but the mean latencies of responses were not significantly different. Stimulation of the thalamic nuclei was more effective than that of the cortical areas both in grafted and intact barrel fields. Posttetanic depression after repetitive stimulation was often observed in the grafts, while posttetanic potentiation was more usual for the intact barrel field. The data show the sources of some functional afferent inputs to the grafts which may be responsible for neuronal reactions to somatosensory stimulation of the host animal.     

Analysis of conduction of visual,somatic, and audiovibratory sensory information to the hippocamapal cortex in lizards

Acute electrophysiological experiments on lizards (Ophisaurus apodus) showed that electrical stimulation of the anterior dorsolateral thalamic nucleus and medial forebrain bundle evokes short-latency responses in the hippocampal (mediodorsal) cortex which coincides in distribution and configuration with responses in the same cortical area to sensory stimulation. Extensive destruction of these structures inhibits, or even completely blocks, the conduction of sensory (visual, somatic, audiovibratory) and tactile impulses to the hippocampal cortex. It is concluded that the anterior dorsolateral thalamic nucleus and medial forebrain bundle constitutes, if not the only, at least the principal pathway for transmission of these sensory impulses to the hippocampal cortex in lizards.     

Distribution of specific signals of different modality in the associative parietal area of the cat cortex

In cats under nembutal anesthesia eliciting specific early components of association responses, the drug parietal distribution upon forepaw and thalamic stimulation was studied: relay somatic-ventrobasal complex (VB) and association nuclei, transmitting specific visual impulses in pulvinar (Pul) and lateral-posterior (LP) areas. Signals of maximum intensity were observed in response to peripheral and central stimulation near somatic area and in response to Pul and LP stimulation in the medial part of parietal cortex. Besides, a general principle revealing more intensive signals of different modality in the areas near lateral sulcus than in other parietal areas was established. The difference in processing of specific polysensory signals in various parietal areas and consequently, different involvement of the latter into the systemic action of the brain was proved, this being related to the character of topical organization of these signals.     

Effect of injury to the lateral reticular nucleus and nuclei of the inferior olive on electrical responses of the cerebellar cortex evoked by vagus nerve stimulation in cats

The role of the lateral reticular nucleus and nuclei of the inferior olive in the formation of cerebellar cortical evoked potentials in response to vagus nerve stimulation was determined in experiments on 28 cats anesthetized with chloralose and pentobarbital. After electrolytic destruction of the lateral reticular nucleus, in response to vagus nerve stimulation, especially ipsilateral, lengthening of the latent period and a decrease in amplitude of evoked potentials were observed; after bilateral destruction of this nucleus, evoked potentials could be completely suppressed. It is concluded that the lateral reticular nucleus relays interoceptive impulses in the vagus nerve system on to the cerebellar cortex. Additional evidence was given by the appearance of spike responses of Purkinje cells, in the form of mainly simple discharges, to stimulation of the vagus nerve. After destruction of the nuclei of the inferior olive, the latent period and the number of components of evoked potentials in response to vagus nerve stimulation remained unchanged but their amplitude was reduced. The role of the nuclei of the inferior olive as a regulator of the intensity of the flow of interoceptive impulses to the cerebellum is discussed.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 290–299, May–June, 1977.     

Organization of the Connections between the Parietal Associative Zone and the Primary Sensory Zones in the Cat Neocortex

In acute experiments on cats, we studied the impulse activity of 262 neurons of the parietal associative zone (PAZ, field 5). Among them, 129 cells [100 silent units and 29 units generating background activity (BA)] were identified as output neurons, while 133 cells with the BA were interneurons of the intrinsic cortical neuronal circuits. Electrical stimulation of the primary visual, auditory, or somatosensory cortices evoked no impulse responses in silent output PAZ neurons, while output neurons with the BA and interneurons (more than 65 and 80% of the cell units, respectively) generated clear responses (more frequently, phasic). Stimulation of the auditory and visual cortices exerted mostly inhibitory effects, while stimulation of the somatosensory cortex provided mostly excitatory influences. The ratios of neurons generating primary excitatory and inhibitory responses to stimulation of the visual, auditory, and somatic cortices were 0.3:1, 0.6:1, and 3.2:1, respectively. More than 95% of the field-5 neurons were influenced from the primary sensory zones via di- and/or polysynaptic pathways. Monosynaptic excitatory inputs from the visual cortex were identified for 3.8% of interneurons and 6.9% of output PAZ neurons; for the auditory cortical inputs, the respective figures were 1.7 and 3.5%. Monosynaptic connections with the somatic cortex were found only for 4% of the interneurons under study. It has been concluded that interaction of heteromodal signals coming to the PAZ via the corticopetal and associative inputs occurs on neurons of all the cortical layers.     

Synaptic effects induced in efferent neurons of the parietal associative cortex of the cat by stimulation of the cerebellar nuclei

Properties of EPSP, evoked in efferent neurons of the parietal associative cortex by stimulation of the cerebellar nuclei, were studied in acute experiments on anesthetized and immobilized cats; intracellular recording was used. The neurons were identified by their antidromic activation after stimulation of the motor cortex, pontinen.n. proprii, or red nucleus. The effects of stimulation of the cerebellar nuclei were of oligo- and polysynaptic nature. The latencies of cerebellofugal EPSP correlated with the latencies of antidromic activation, and correlations were significant both in the cases when the effects of stimulation of separate efferent projections (cortico-cortical, cortico-pontine, or cortico-rubral) and the effects of stimulation of separate cerebellar nuclei were analyzed. The functional role of the efferent systems of the parietal associative cortex and significance of functional parameters of the neurons constituting these systems are discussed.Neirofiziologiya/Neurophysiology, Vol. 27, No. 3, pp. 190–198, May–June, 1995.     

Characteristics of dorsal horn neurons expressing subliminal responses to sural nerve stimulation

The present study was designed (1) to characterize the subliminal responses of dorsal horn neurons to stimulation of the sural nerve, and (2) to correlate the type of response to this stimulus with the responses to natural mechanical stimulation of the skin. To accomplish this, intracellular and extracellular recordings were carried out in L6 and L7 dorsal horn neurons in the cat. The excitatory responses of each cell to electrical stimulation of the sural nerve and to mechanical stimulation of the skin were noted. Of 35 dorsal horn cells recorded intracellularly, 11 responded with impulses to sural nerve stimulation, 9 responded with excitatory postsynaptic potentials (EPSPs) but not impulses, and 15 had no excitatory responses to this stimulus. The type of response to sural nerve stimulation was strongly correlated with receptive field modality. Most cells receiving an input from high-threshold cutaneous mechanoreceptors responded with impulses or gave no excitatory response to sural nerve stimulation, whereas most cells that had only low-threshold mechanoreceptor input responded with EPSPs only or gave no response. In cells with only low-threshold (LT) mechanoreceptive input, response to sural nerve stimulation was highly correlated with receptive field locus. Those LT cells with no excitatory responses to sural nerve stimulation had receptive fields confined to the foot and/or toes, whereas those that gave EPSPs had more proximal receptive fields. The possible significance of these data with reference to changes observed after lesions, such as increased response to sural nerve stimulation, increased receptive field size, and somatotopic reorganization, is discussed.     

15th Annual spring brain conference,march 10–13, 2004,summary report

The present study was designed (1) to characterize the subliminal responses of dorsal horn neurons to stimulation of the sural nerve, and (2) to correlate the type of response to this stimulus with the responses to natural mechanical stimulation of the skin. To accomplish this, intracellular and extracellular recordings were carried out in L⁶ and L⁷ dorsal horn neurons in the cat. The excitatory responses of each cell to electrical stimulation of the sural nerve and to mechanical stimulation of the skin were noted.

Of 35 dorsal horn cells recorded intracellularly, 11 responded with impulses to sural nerve stimulation, 9 responded with excitatory postsynaptic potentials (EPSPs) but not impulses, and 15 had no excitatory responses to this stimulus. The type of response to sural nerve stimulation was strongly correlated with receptive field modality. Most cells receiving an input from high-threshold cutaneous mechanoreceptors responded with impulses or gave no excitatory response to sural nerve stimulation, whereas most cells that had only low-threshold mechanoreceptor input responded with EPSPs only or gave no response. In cells with only low-threshold (LT) mechanoreceptive input, response to sural nerve stimulation was highly correlated with receptive field locus. Those LT cells with no excitatory responses to sural nerve stimulation had receptive fields confined to the foot and/or toes, whereas those that gave EPSPs had more proximal receptive fields. The possible significance of these data with reference to changes observed after lesions, such as increased response to sural nerve stimulation, increased receptive field size, and somatotopic reorganization, is discussed.     

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.     

Basal ganglia influences on the cerebellum of the cat

The changes in firing rate of intracerebellar nuclear neurons following electrical stimulation of the contralateral basal ganglia were investigated in adult cats, in which antidromic activation of cortico-pontine and/or cortico-olivar fibers arising in the area 6 had been excluded by chronic ablation of the motor cortex. Activation of putamen and caudate nucleus induced discharge changes in a low percentage (below 12.5%) of both medial and lateral cerebellar nuclei neurons, while stimulation of globus pallidus and especially of entopeduncular nucleus modified the spontaneous discharge of a greater percent of cells (up to 29%), mainly in the most lateral cerebellar portions. The basal ganglia-induced effects were abolished upon section of the brachium pontis but not of the restiform body. Latency values of the responses, which were predominantly excitatory in nature, suggest the involvement of structures interposed between basal ganglia and precerebellar systems. We postulated that impulses issued by the basal ganglia could reach the cerebellum through a pathway that involves the pedunculopontine nucleus and the nucleus reticularis tegmenti pontis.     

Neurophysiologic analysis of the bilateral organization of the associative parietal regions of the neocortex in the cat

In cats under Nembutal anesthesia, impulses come to the parietal areas of both hemispheres, which, when evoked by unilateral stimulation of fore- and hind-paws, converge at the same cortical points forming early components of associative responses (ECAR). In responses to contralateral paws' stimulation, individual interhemispheric functional asymmetry is shown. The influence of the contralateral parietal area on the ipsilateral one is more strong than the reverse effect. In contrast to ECAR formation on the contralateral side as a result of the arrival of impulses of specific genesis along the "classical" lemniscal tract,--the signals of the same type participating in the initiation of ECAR in the ipsilateral hemisphere, on their way form a relay in the thalamus and the same zone of the opposite side via the interthalamic commissure and callosal body, correspondingly. It is suggested that along with the arrival of impulses through the mentioned crossed tracts, ECAR generation in the ipsilateral parietal cortex involves impulses, coming through the uncrossed channel of the extralemnisc tract.     

Analysis of evoked potentials from the limbic cortex

In acute experiments on cats we investigated evoked potentials from the cingulate gyrus developed in response to stimulation of somatic and visceral nerves; also potentials from various parts of the hypothalamus, and midbrain reticular formation. We showed that the nonspecific afferent system influences electrical activity in the limbic cortex through hypothalamic pathways. We consider the limbic cortex to be part of the association area of the neocortex and that the associative responses of the cortex are more complex in nature than is usually thought to be the case, and that they are formed under the influence of impulses arriving at the cortex along many specific and nonspecific pathways. The hypothalamo—cingulate system is one of the main systems of cortico—subcortical integration. It plays an important part in regulation of autonomic, somatic, and emotional responses.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 2, No. 5, pp. 451–459, September–October, 1970.     

Changes in the evoked potentials in the visual and association cortex of the alert cat after changing the order of stimulation of the lateral geniculate body and superior colliculi

In chronic experiments on alert cats the preceding stimulation of the lateral geniculate body (LGB) facilitates the response in the visual cortex to testing stimulation of the anterior colliculi (AC) at all studied delays between stimuli in contrast to the associative cortex where this response has been depressed in intervals of 10-40 ms. In reverse order of stimulation, facilitation of response to testing LGB stimulation is observed at all studied delays in the associative cortex, while in the visual cortex this response is slightly depressed. The obtained data point to the importance of the information coming in the accessory zones of LGB and AC projections and to different informational value of AC inputs to the associative and visual cortices and reciprocal relations between inputs to these cortical areas from LGB and AC.     

Connections of thalamic nucleus lateralis posterior with suprasylvian cortex in cats

Cats were immobilized with D-tubocurarine. Responses of 231 neurons of the thalamic nucleus lateralis posterior to cortical stimulation in areas 5b and 21 of the suprasylvian gyrus were studied. Responses of 34 neurons were antidromic, indicating the existence of a direct projection of this nucleus to the cortical areas studied. This projection was most extensive in area 5b. The long latencies (up to 60 msec) of the antidromic responses of some neurons indicate that axons of certain neurons of thalamic nucleus lateralis posterior conduct excitation very slowly (0.3 m/sec). Orthodromic responses with latencies of 2–3 msec to cortical stimulation point to the presence of direct pathways from cortex to nucleus. The flow of afferent impulses into the nucleus from area 5b is stronger than from area 21. Convergence of impulses from these areas was observed on 44% of neurons of the nucleus. Cortical stimulation of areas 5b and 21 evoked postsynaptic inhibition in most neurons of the nucleus. It is concluded that two-way direct connections exist between nucleus lateralis posterior of the thalamus and the suprasylvian cortex.     

Unit responses of the cat somatosensory cortex to stimulation of the reticular and anteroventral thalamic nuclei

Responses of 189 neurons of the somatosensory cortex to stimulation of the nonspecific reticular (R) and anteroventral (AV) nuclei of the thalamus were studied in cats anesthetized with thiopental and immobilized with tubocurarine. In the series of experiments with stimulation of R and, for comparison, of the specific ventral posterolateral nucleus (VPL), 132 neurons were recorded, of which 22 (16.7%) did not respond to stimulation of these nuclei, 77 (58.3%) responded only to stimulation of VPL, and 33 (25%) responded to stimulation of both VPL and R. In the series of experiments in which AV was stimulated, 57 neurons were recorded. Eight (14.8%) responded to neither stimulus and 25 (43.1%) responded only to stimulation of VPL; 24 responded to stimulation of AV (42.1%), and of these, 10 also responded to stimulation of VPL. A characteristic feature of unit responses in the somatosensory cortex to stimulation of the nonspecific nuclei was the irregularity of the responses and their longer latent period. Only five cells responded sooner to stimulation of the nonspecific nuclei than to stimulation of VPL. Responses of the nonspecific nuclei to stimulation appeared clearly only if the stimulation was repetitive. Preliminary stimulation of R blocks the response to stimulation of VPL during the subsequent 40–60 msec.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol.4, No.4, pp. 384–390, July–August, 1972.     

Interaction between unit responses of the cat cerebellar cortex during paired stimulation of the forelimbs

Interaction between spike responses of 41 cerebellar cortical neurons to electrical stimulation of the two forelimbs with different intervals between stimuli were studied in cats anesthetized with chloralose and pentobarbital. The responsiveness of neurons with a phasic type of discharge to testing stimulation of the limb was reduced for 300–500 msec or longer after conditioning stimulation of the other limb. Interaction between the responses was less clear in neurons with a tonic type of response. Interaction was absent or was summating in character if the stimuli were applied at the same times. Only if the intertrial intervals were 50–150 msec was regular inhibition of the responses of tonic type to the testing stimulus observed. It is postulated that the nucleus of the inferior olive participates in the interaction between phasic unit responses during simultaneous stimulation of the two limbs or to stimulation separated by short intervals (under 30 msec). With longer intervals between stimuli, interaction between responses of either type is connected with involvement of the lateral reticular nucleus. In the process of interaction competitive relations may develop between responses caused by impulses reaching neurons of the cerebellar cortex along climbing and mossy fibers.     

Modulation of synaptic plasticity in the hippocampus and piriform cortex by physiologically meaningful olfactory cues in an olfactory association task

Animals were trained to discriminate two natural odors while another group was trained to discriminate between a patterned electrical stimulation distributed on the lateral olfactory tract (LOT), labelled olfaco-mimetic stimulation (OMS), used as an olfactory cue versus a natural odor. No statistically significant difference was observed in behavioral data between these two groups. The animals trained to learn the meaning of the OMS exhibited a gradual long-term potentiation (LTP) phenomenon in the piriform cortex. When a group of naive animals was pseudo-conditioned, giving the OMS for the same number of sessions but without any olfactory training, no LTP was recorded. These results indicate that the process of learning olfactory association gradually potentiates cortical synapses in a defined cortical terminal field, and may explain why LTP in the piriform cortex is not elicited by the patterned stimulation itself, but only in an associative context. As olfactory and hippocampus regions are connected via the lateral entorhinal cortex, the olfactomimetic model was used to study the dynamic of involvement of the dentate gyrus (DG) in learning and memory of this associative olfactory task. Polysynaptic field potentials, evoked by the LOT stimulation, were recorded in the molecular layer of the ipsilateral DG. An early and rapid (2nd session) potentiation was observed when a significant discrimination of the two cues began to be observed. The onset latency of the potentiated response was 30–40 ms. When a group of naive animals was pseudoconditioned, no change was observed. Taken together, these results support the hypothesis that early activation of the DG during the learning of olfactory cue allows the progressive storage of olfactory information in a defined set of potentiated cortical synapses. The onset latency of the polysynaptic potentiated responses suggests the existence of a reactivating hippocampal loops during the processing of olfactory information.