Role of septal and entorhinal inputs in the generation of hippocampal electrical activity in the cat sleep-wake cycle

The effects of septal lesion and entorhinal cortex section on hippocampal electrical activity during the cat sleep-wake cycle were investigated in chronic experiments. The medial portion of the septum only was found to participate in generation of this activity. Complete suppression of hippocampal theta rhythm during active wakefulness and paradoxical sleep were the main effects of septal lesion. In slow-wave sleep, the effects of septal lesion manifested in a slight attenuation of the intensity of the dominant frequency (of 1 Hz). Widespread septal lesion does not add to the changes occurring when the medial portion of the septum is so isolated. Section of the entorhinal cortex produces a sharp increase in hippocampal theta rhythm during waking and paradoxical sleep. Clearcut attenuation of delta and subdelta rhythm intensities were observed in slowwave sleep. It is postulated that under normal conditions hippocampal entorhinal input exerts a modulating effect on the genesis of hippocampal theta rhythm.I. S. Beritashvili Institute of Physiology, Academy of Sciences of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 19, No. 5, pp. 622–630, September–October, 1987.     

Field potentials in the lumbar ventral horn during combined extrapyramidal and cortical stimulation

Field potentials arising in the medial (Rexed's layer VIII) and lateral (region of the flexor motoneuronal nuclei) zones of the ventral horn during stimulation of the motor cortex or ventromedial funiculus in the cervical spinal cord were recorded in experiments on cats. Inhibition of the electrical response in the flexor nerve to stimulation of the contralateral cortex, an indicator of the cortical motor response, can be evoked by stimulation not only of the symmetrical point of the opposite cortex but also of the group of fibers of the ventromedial funiculus connected functionally with that point. In each experiment the fact that these fibers belonged functionally to the system conducting cortically evoked descending influences was verified in each experiment from a combination of specific criteria. Extrapyramidal inhibition of the cortical motor response is accompanied by the same changes in field potential in the medial and lateral zones of the ventral horn as cortical inhibition: by an increase in negativity in the first and by its suppression in the second. The differences between the two types of interaction are concerned chiefly with the temporal course of all the processes studied. The results are used as evidence of the extrapyramidal nature of cortical inhibition of the cortical motor response.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 4, No. 6, pp. 597–607, November–December, 1972.     

Effect of electrical stimulation of the septum on subicular neurons with different kinds of spontaneous activity in rabbits

The effect of electrical stimulation of the medial nucleus of the septum and of hippocampal area CA₁ on subicular neurons with three different types of spontaneous activity (with theta-modulation, with delta-modulation and complex spikes, and with irregular single-spike activity) was studied in unanesthetized rabbits by extracellular recording of unit activity. Cells with theta-activity were found to respond in a distinctive functional manner to stimulation of the medial nucleus of the septum: Their reactivity was higher but latent periods of their responses were much shorter than those of cells with delta-activity and irregular discharges. Stability of modulation of theta-cell activity increased both during and after stimulation of the medial septal nucleus. Electrical stimulation of hippocampal area CA₁, on the other hand, led to disappearance of rhythm modulation. Average response latencies of all three types of cells to stimulation of area CA₁ were equal. The results indicate special properties of the septal input to subicular cells with theta-modulation.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 326–333, May–June, 1985.     

Effect of the vermian cortex of the anterior lobe of the cerebellum on the background electrical activity of fastigial neurons

The effect of electrical stimulation of the vermian cortex of the anterior lobe of the cerebellum on the activity of neurons of different portions of the fastigial nucleus was studied in acute experiments on cats under light nembutal anesthesia. Inhibitory influences of the cortex (80.6% of the reacting neurons) were manifested in total blocking or decrease in the frequency of the background activity of the neurons and were characterized by a long aftereffect and "rebound." Stimulation of the cortex also had a blocking effect on the inhibitory interaction of adjacent nuclear elements. Facilitatory influences (14.5% of the neurons) were expressed either by an increase of spontaneous discharges of the neurons or by the appearance of activity in rhythm with the stimulation. The effectiveness of cortical stimulation depended on the localization of the stimulating electrodes. Zones of maximum density of projections to a given neuron of the nucleus and convergence and divergence of influences were found in the cerebellar cortex.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziolgiya, Vol. 2, No. 3, pp. 260–268, May–June, 1970.     

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.     

Depression of evoked potentials in rat thalamic ventro-basal complex and somatosensory cortex after reticular stimulation

Experiments on unanesthetized rats immobilized with D-tubocurarine showed that electrical stimulation (100/sec) of the central gray matter and the mesencephalic and medullary reticular formation considerably depressed potentials in the somatic thalamic relay nucleus and somatosensory cortex evoked by stimulation of the forelimb or medial lemniscus. The mean threshold values of the current used for electrical stimulation of these structures did not differ significantly and were 70 (20–100), 100 (20–120), and 120 (50–200) µA, respectively. On comparison of the amplitude-temporal characteristics of inhibition of evoked potentials during electrical stimulation of the above-mentioned structures by a current of twice the threshold strength, no significant differences were found. Immediately after the end of electrical stimulation the amplitude of the cortical evolved potential and the post-synaptic components of the thalamic evoked potential was 50–60% (P<0.01) below the control values. The duration of this depression varied from 0.5 to 1 sec. An increase in the intensity of electrical stimulation of brain-stem structures to between three and five times the threshold led to depression of the presynaptic component of the thalamic evoked potential also. Depression of the evoked potential as described above was found with various ratios between the intensities of conditioning and testing stimuli.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 5, pp. 467–475, September–October, 1976.     

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.     

Effect of regular electrical stimulation of the septum on defensive conditioning

A conditioned defensive reflex to photic stimulation was produced in rabbits in computer-controlled experiments during regular electrical stimulation of the septum. During reflex formation spectral-correlation analysis was undertaken of sensomotor and visual cortical potentials and hippocampal potentials. In each rabbit the reflex to light was produced during septal stimulation at a definite frequency (2, 4, 7, and 9 Hz). Regular electrical stimulation of the septum at frequencies of 7 and 9 Hz accelerated conditioning whereas stimulation at a frequency of 2 Hz prevented formation of the temporary connection (the reflex appeared at the 35th combination). By changing the frequency of electrical stimulation of the septum, the speed of learning can thus be influenced. It is suggested that the role of the septum is to set a definite level of synchronization of brain processes at the optimal value for conduction of excitation from its afferent to its effector system.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 239–244, May–June, 1978.     

Producing the cortical phenomenon of "kindling" during acute experiments on cats

Acute experiments on cats enabled spontaneous epileptogenic foci to be produced by means of electrical stimulation of the cerebral cortex. The central area of the suprasylvian gyrus was stimulated by 5-sec stimuli at 3-sec intervals. The strength of neuronal response gradually increased until spontaneous electrical activity set in as stimulation was set at a fixed intensity which had originally evoked local residual discharge at stimulation foci only, i.e., the phenomenon of "kindling" was observed. When "kindling" was produced in the cortical area under study, bursts of spindle activity were recorded on all ECoG with increasing frequency. Recordings of spindle activity then changed to a "spike-wave" pattern of activity. The results of these investigations, which were performed on an isolated strip of cortex, point to the involvement of subcortical structures in mediating "kindling" of the cortical focus.Institute of Clinical and Experimental Neurology, Ministry of Public Health of the Georgian SSR, Tbilisi. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 601–606, September–October, 1985.     

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.     

Neuronal responses of a chronically isolated slab of auditory cortex to intracortical stimulation during paroxysmal electrical activity in cats

Responses of 155 neurons 3 weeks after neuronal isolation of a slab of auditory cortex (area AI) to single intracortical stimulating pulses at the level of layer IV were studied in unanesthetized, curarized cats during paroxysmal electrical activity evoked by series of high-frequency (10–20 Hz) electrical stimulation by a current 2–5 times above threshold for the direct cortical response. In response to such stimulation a discharge of paroxysmal electrical activity, lasting from a few seconds to tens of seconds, appeared in the slab. As a rule it consisted of two phases — tonic and clonic. This indicates that cortical neurons can form both phases of paroxysmal cortical activity. Depending on behavior of the neurons during paroxysmal electrical activity and preservation of their ability to respond to intracortical stimulation at this time, all cells tested in the isolated slab were divided into four groups. Their distribution layer by layer and by duration of latent periods was studied. Two-thirds of the neurons tested were shown to generate spike activity during paroxysmal discharges whereas the rest exhibited no such activity. A special role of neurons in layer II in generation of paroxysmal activity in the isolated slab was noted. The view is expressed that at each moment functional neuronal circuits, independent of each other, exist in the slab and also, evidently in the intact cortex, which can interact with one another when conditions change.I. I. Mechnikov Odessa State University. Translated from Neirofiziologiya, Vol. 16, No. 1, pp. 3–11, January–February, 1984.     

Visual cortex contribution to the organization of eye movements produced by local electrical stimulation of the cat lateral geniculate body

Eye movements evoked by local electrical stimulation of the dorsal nucleus of the lateral geniculate body were analyzed after removal of the visual cortex and in intact animals during trials on awake cats. No significant difference was observed between the eye movement patterns of the two animal groups evoked by electrical stimulation. These movements could be classed into three main groups: those unassociated with the starting position of the eyes in orbit (or unidirectional movements), goal-directed, and centered movements, with direction depending on the initial position of the eyes in their orbits. Our findings indicate that the cortical visual areas are neither the principal nor an indispensable link in the chain for transmitting signals evoked by (electrically) stimulating the geniculate body from the cortical structures of the direct visual pathway towards the operative links of the oculomotor system. Potential pathways for conducting information from the dorsal nucleus of the lateral geniculate body to oculomotor system structures are discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 164–170, March–April, 1987.     

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.     

Comparison of fMRI BOLD Response Patterns by Electrical Stimulation of the Ventroposterior Complex and Medial Thalamus of the Rat

The objective of this study was to compare the functional connectivity of the lateral and medial thalamocortical pain pathways by investigating the blood oxygen level-dependent (BOLD) activation patterns in the forebrain elicited by direct electrical stimulation of the ventroposterior (VP) and medial (MT) thalamus. An MRI-compatible stimulation electrode was implanted in the VP or MT of α-chloralose-anesthetized rats. Electrical stimulation was applied to the VP or MT at various intensities (50 µA to 300 µA) and frequencies (1 Hz to 12 Hz). BOLD responses were analyzed in the ipsilateral forelimb region of the primary somatosensory cortex (iS1FL) after VP stimulation and in the ipsilateral cingulate cortex (iCC) after MT stimulation. When stimulating the VP, the strongest activation occurred at 3 Hz. The stimulation intensity threshold was 50 µA and the response rapidly peaked at 100 µA. When stimulating the MT, The optimal frequency for stimulation was 9 Hz or 12 Hz, the stimulation intensity threshold was 100 µA and we observed a graded increase in the BOLD response following the application of higher intensity stimuli. We also evaluated c-Fos expression following the application of a 200-µA stimulus. Ventroposterior thalamic stimulation elicited c-Fos-positivity in few cells in the iS1FL and caudate putamen (iCPu). Medial thalamic stimulation, however, produced numerous c-Fos-positive cells in the iCC and iCPu. The differential BOLD responses and c-Fos expressions elicited by VP and MT stimulation indicate differences in stimulus-response properties of the medial and lateral thalamic pain pathways.     

Evoked activity in the ventral horn of the lumbar segments of the spinal cord during cortical inhibition of cortical motor responses

Electrical activity in the flexor nerve and focal potentials (FP) in the medial and lateral zones of the ventral horn (VH) of segments L₆ and L₇ of the spinal cord, evoked by excitation of the contralateral motor cortex, were recorded in delicate experiments on cats. These focal potentials were studied during inhibition of the flexor response that developed as a result of prior excitation of the ipsilateral cortex ("cortical inhibition"). During the inhibition the FP's of the medial zone (layer VIII, according to Rexed) were greatly increased, mainly in their negative components, their time-characteristics being altered. When the interval between excitations was 50 msec (in that case the inhibition was most pronounced) the medial FP's arose against a negative background, which was a late component of the previous activity evoked by conditioning excitation. The appearance of this late component was correlated with the development of inhibition of the cortical flexor response. At the same time a positive condition developed in the lateral zone, in the region of the nucleus biceps-semitendinosus, which indicated orientation in a lateral direction of the interneurons discharging in the medial zone at late periods after the conditioning excitation. Inhibition of the flexor response was accompanied by depression of the lateral FP's without change in their sign or in the time-structure of their components. It is suggested that cortical inhibition of the cortical flexor response arises at the interneuron level. The functional structure of that inhibitory pathway is discussed.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 185–193, March–April, 1971.     

Direct cortical response in the cat motor cortex during summation

Summation was studied by a procedure close to that used in producing a conditioned reflex. Subthreshold electrical stimulation, which gave rise to a dominant focus in the cat motor cortex, was applied after photic stimulation. Under these conditions, summation occurred both when the two stimuli were applied simultaneously and when the weaker stimulus preceded the stronger one by a very short interval (tens of milliseconds). Increased excitability was characteristic of the dominant focus. An excessive increase in excitability weakened the summation reflex. Electrographically, this type of conditioning was reflected in an increase in amplitude of the primary negative wave of the direct cortical response, recorded in the motor area at a distance of 2–3 mm from the stimulation point. It is concluded from analysis of this electrophysiological phenomenon and comparison of the results with data in the literature that different mechanisms are involved in the summation process during different sequences of stimulation ("photic+electrical" and "electrical+photic").Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 293–302, November–December, 1969.     

Unit responses in the cat auditory cortex to medial geniculate body stimulation

Responses of 98 auditory cortical neurons to electrical stimulation of the medial geniculate body (MGB) were recorded (45 extracellulary, 53 intracellularly) in experiments on cats immobilized with tubocurarine. Responses of the same neurons to clicks were recorded for comparison. Of the total number of neurons, 75 (76%) responded both to MGB stimulation and to clicks, and 23 (24%) to MGB stimulation only. The latent period of extracellularly recorded action potentials of auditory cortical neurons in response to clicks varied from 7 to 28 msec (late responses were disregarded), and that to MGB stimulation varied from 1.5 to 12.5 msec. For EPSPs these values were 8–13 and 1–4 msec respectively. The latent period of IPSPs arising in response to MGB stimulation varied from 2.2 to 6.5 msec; for 34% of neurons it did not exceed 3 msec. The difference between the latent periods of responses to clicks and to MGB stimulation varied for different neurons from 6 to 21 msec. Responses of 11% of neurons to MGB stimulation, recorded intracellularly, consisted of sub-threshold EPSPs, while responses of 23% of neurons began with an EPSP which was either followed by an action potential and subsequent IPSP or was at once cut off by an IPSP; 66% of neurons responded with primary IPSPs. Neurons responding to MGB stimulation by primary IPSPs are distributed irregularly in the depth of the cortex: there are very few in layers III and IV and many more at a depth of 1.6–2 mm. Conversely, excited neurons are predominant in layer III and IV, and they are few in number at a depth of 1.6–2 mm. It is concluded that the afferent volley reaching the auditory cortex induces excitation of some neurons therein and, at the same time, by the principle of reciprocity, induces inhibition of others. This afferent inhibition takes place with the participation of inhibitory interneurons, and in some cells the inhibition is recurrent. The existence of reciprocal relationships between neurons in different layers of the auditory cortex is postulated.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 23–31, January–February, 1972.     

Two patterns of bulbar neuronal response to microstimulation of locomotor and inhibitory brain stem sites

Synaptic responses (postsynaptic potentials and action potentials) were evoked in mesencephalic decerebellated cats by stimulating pontine bulbar locomotor and inhibitory sites (LS and IS, respectively) with a current of not more than 20 µA in "medial" and "lateral" neurons of the medulla. Some neurons even produced a response to presentation of single (actually low — 2–5 Hz — frequency) stimuli. The remaining cells responded to stimulation at a steady rate of 30–60 Hz only. Both groups of medial neurons were more receptive to input from LS. Lateral neurons responding to even single stimuli reacted more commonly to input from LS and those responding to steady stimulation only to input from IS. Many neurons with background activity (whether lateral or medial) produced no stimulus-bound response, but rhythmic stimulation either intensified or inhibited such activity. This response occurs most commonly with LS stimulation. Partial redistribution of target neurons in step with increasing rate of presynaptic input may play a major part in control of motor activity.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 257–266, March–April, 1990.     

Modulation of pyramidal response in the rat sensorimotor cortex after combined stimulation of the lateral hypothalamus and the sensorimotor cortex

It was shown during experiments on unrestrained rats that rhythmic stimulation of the pyramidal tract produced a statistically significant increase in the functional activity of neuronal populations of the sensorimotor cortex, manifesting as potentiation of the primary, positive phase of pyramidal cortical response. Combined rhythmically matched stimulation of the pyramidal tract and of the lateral hypothalamus leads to statistically significant enhancement in potentiation of the positive phase of pyramidal cortical response compared with effects produced independently of hypothalamic involvement. When stimulation of the pyramidal tract and the lateral hypothalamus are combined with stimulation applied at the same periodicity to the sensorimotor cortex, a further statistically significant enhancement in potentiation of the positive phase of pyramidal cortical response is seen in addition to the potentiating effect produced by hypothalamic stimulation.Institute for Brain Research of the All-Union Scientific Center of Mental Health, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 367–373, May–June, 1986.     

Unit responses in area 5b of the suprasylvian gyrus to stimulation of the posterior lateral thalmamic nucleus

In response to stimulation of the posterior lateral nucleus in unanesthetized cats immobilized with D-tubocurarine an evoked potential consisting of three components with a latent period of 3–5 msec appeared in area 5b of the suprasylvian gyrus. All three components were reversed at about the same depth in the cortex (1500–1600 µ). Reversal of the potential shows that it is generated in that area by neurons evidently located in deeper layers of the cortex and is not conducted to it physically from other regions. Responses of 53 spontaneously active neurons in the same area of the cortex to stimulation of the posterior lateral nucleus were investigated. A characteristic feature of these reponses was that inhibition occurred nearly all of them. In 22 neurons the responses began with inhibition, which lasted from 30 to 400 msec. In 30 neurons inhibition appeared immediately after excitation while one neuron responded by excitation alone. The latent periods of the excitatory responses varied from 3 to 28 msec. The short latent period of the evoked potentials and of some single units responses (3–6 msec) confirms morphological evidence of direct connections between the posterior lateral nucleus and area 5b of the suprasylvian gyrus. Repetitive stimulation of that nucleus led to strengthening of both excitation and inhibition. Influences of the posterior lateral nucleus were opposite to those of the specific nuclei: the posterior ventrolateral nucleus and the lateral and medial geniculate bodies. Stimulation of the nonspecific reticular nucleus, however, evoked discharges from neurons like those produced by stimulation of the posterior lateral nucleus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 502–509, September–October, 1973.