Stimulation Of Thalamic Nuclei Research Articles

Evoked responses to electrical stimulation of the auditory pathway during the wake/sleep cycle

Cats with chronically implanted electrodes were used to study changes in the auditory pathway during the wake/sleep cycle. Evoked responses to electrical stimulation of brain stem and thalamic nuclei were recorded and the animals' state of arousal was determined by observation and by monitoring EEG and EMG. Evoked responses in superior olive and inferior colliculus were invariant during the wake/sleep cycle. Evoked responses in medial geniculate and auditory radiations showed significant changes in slow wave sleep compared with wakefulness when stimulated from nuclei below inferior colliculus. However, with inferior colliculus stimulation, no significant changes in response at medial geniculate or radiations were observed. Evoked responses recorded from posterior A1 cortical sites showed increased amplitude of the late wave and simplification of the early biphasic waves during slow wave sleep. In contrast, evoked responses recorded from Ep and anterior A1 sites decreased in amplitude or were absent during slow wave sleep compared to responses recorded during wakefulness. No significant differences between evoked responses recorded at cortex during wake or REM sleep were obtained. It is suggested that in the auditory system, the major changes occurring during the wake/sleep cycle are cortical in origin, and sub-areas of auditory cortex change differentially. Some change is also observed in medial geniculate only if stimulation is below the level of inferior colliculus.

Thalamo-amygdalar relationships. An evoked potential study

Stimulation of dorsal thalamic nuclei from rostral to caudal and mediolateral levels in cats under chloralose anesthesia consistently evoked responses from the basal nucleus of the amygdala. These responses varied in waveform and latency with respect to different functionally distinct thalamic nuclear groups. Within these groups certain characteristics were observed. Stimulation of the anterior reticular (prothalamic), anterior, and ventral anterior nuclei evoked medium to high spike-like responses of short latency indicating a possible direct relationship to the amygdala. Stimulation of the extrinsic relay nuclei evoked the most distinctive responses from the amygdala in the form of relatively high amplitude (75–150 μV) sharply peaked responses of medium latency (11–20 msec). Associational nuclei (LD, LP) evoked medium slow wave responses of long latency. Stimulation of dorsomedial, midline, centromedian, and parafascicular nuclei evoked amygdalar responses of low to medium amplitude and of slow-wave type having mixed latency.

Primary afferent depolarization in the cuneate nucleus induced by stimulation of cerebellar and thalamic non-specific nuclei

It has been observed that, in cats under Nembutal anaesthesia, stimulation of the cerebellar and non-specific thalamic nuclei can induce depolarization of the afferents to the cuneate nucleus. This depolarization has been evidenced by: (1) increase in the excitability of the afferent terminals as revealed by Wall's technique; (2) appearance of a negative slow potential in the dorsal columns; (3) field potentials in the nucleus itself. The cerebellar effects, which were maximal after stimulation of n. fastigii, were present even after acute decerebration and were mainly mediated by the inferior cerebellar peduncle. The thalamic effects were still present after ablation of the sensorimotor cortex and of the basal ganglia. The hypothesis advanced is that both thalamic and cerebellar effects are mediated by the bulbopontine reticular formation.

Cortical synchronization induced by high frequency thalamic stimulation

A peculiar spindle-shaped form of activity composed of high amplitude, slow (3–7/sec), surface negative or biphasic waves could be induced by high frequency electrical stimulation of midline thalamic nuclei on free-moving animals. The appearance of this spindle-like activity depended on the intensity of stimulation. By systematic variation of the stimulus frequency it was found that any frequency above about 5/sec was capable of inducing spindle-like activity if the stimulus intensity was sufficiently strong. In the case of consecutive stimulations, the subsequent stimulation produced spindle-like activity only if it was applied after a 10–60 sec pause. This spindle-like activity never occurred under barbiturate narcosis, but regularly appeared in awake, immobilized animals.

Characteristic features of augmenting and recruiting responses in the cerebral cortex

Laminar field potentials in the cerebral cortex elicited by repetitive stimulation of thalamic nuclei (6–9/sec) were studied and used to define so-called augmenting and recruiting responses. Deep and superficial thalamocortical responses were first distinguished since they were recognized as elementary components of all cortical responses evoked by the repetitive thalamic stimulation. Augmenting responses were then defined as a succession of the deep and superficial thalamocortical responses and recruiting responses as a pure form of the superficial thalamocortical response. There were presented several examples which indicate the usefulness of laminar field potentials in the analysis of complicated cortical responses elicited by the repetitive thalamic stimulation, e.g., mixtures of augmenting and recruiting responses, exceptionally long latency augmenting responses and very short latency recruiting responses. Laminar field potential study with the aid of such definitions of augmenting and recruiting responses was especially advantageous in the analysis of complex potentials generated around a hidden cortex and in the localization of true active areas in the cortex. The definitions of augmenting and recruiting responses made on laminar field potentials were demonstrated to be consistent in interpretation of various cortical responses provoked in different situations by the repetitive thalamic stimulation. This study indicates the existence of two different thalamocortical projection systems responsible for the deep and superficial thalamocortical responses.

Recruiting responses in the cerebral cortex produced by putamen and palldium stimulation : G. Dieckmann and K. Sasaki (Frankfurt am Main, W. Germany)

1. Field potentials in the cerebral cortex elicited by low frequency (6–10/sec) repetitive stimulation of the putamen (Put) and pallidum (Pal) were recorded by glass microelectrodes inserted at various depths in the cortex and analysed together with those evoked by stimulation of different thalamic nuclei. Surface cortical potentials recorded by a gross electrode and intracellular potential changes in cortical neurones were also provided to complement field potential analysis. 2. Stimulation of putamen or pallidum produced characteristic laminar field potentials which were similar to those elicited by stimulation of the centrum medianum (CM) nucleus in the thalamus. Superficial slow negative and deep positive potentials showed much the same time course as in a mirror image and the polarity change at 0.10–0.25 mm depth in the cortex. These profiles of field potentials indicate that putamen- and pallidum-induced potentials are pure recruiting responses in every respect. Latency of Put-induced responses was always longer than that of Pal- and CM-induced responses, the latter two being comparable. Duration was wider in the responses evoked by CM stimulation than those by Put and Pal. The optimal frequency for Put- and Pal-induced recruiting responses was 7–9/sec and the same as that for CM-induced responses in every experiment. 3. Current spread of Put and Pal stimulation to surrounding structures such as the internal capsule was outruled, since entirely different responses (augmenting responses) could be evoked in the cortex by stimulation of the internal capsule delivered through the same electrode after withdrawal of the electrodes by 1–2 mm from Put and Pal to the internal capsule. 4. The cortical area in which Put- and Pal-evoked recruiting responses were recorded was more restricted than the area for CM-induced recruiting responses and was mainly in area 6 a β. 5. The results lead us to refer to and discuss a hypothesis for the pathways of CM-induced recruiting responses that has been made on previous anatomical findings.

On the Evolution of the Integrative Activity of the Central Nervous System in the Phylogeny of Vertebrates

This chapter analyzes the functional and structural organization of some parts of the central nervous system, in a series of animals constituting the basic stages of the evolution, which is acrania, cyclostomata, crosstomata, reptiles, and lower mammals. In amphyoxus lunceolutus , the responses to light or electrical stimulation of both the head and the tail of the nervous tube were of the same intensity. These reactions persisted even after surgical disconnection of the nervous tube. Combination of unconditioned and conditioned stimulation of the disconnected parts of the head and tail end of amphyoxus resulted in the formation of temporary connections. This proves that the central nervous system of amphyoxus is diffuse with no functional localization. In Cyclostomata, despite differentiation and formation of various parts of the central nervous system, the elements of diffuseness are still inherent. The experiments performed on reptiles ( varanus griseus ) demonstrated that stimulation of the dorsal thalamus evokes recruiting responses in the anterior and medial parts of the common and hippocampal cortex with a latency of 8–30 msec. The experiments carried out on rats and cats showed that low-frequency stimulation of nonspecific thalamic nuclei evokes responses in different cortical areas, different in their latency and the degree of recruiting.

Some problems associated with interpretation of physiological and behavioral responses to stimulation of caudate and thalamic nuclei

Low frequency electrical stimulation of the caudate nucleus or ventral lateral or ventral anterior nucleus of the thalamus inhibits the performance of learned behavior. Concomitant with the behavioral inhibition and elicited by stimuli of the same intensity, is an electrophysiological response consisting of inhibition of unit activity and an associated slow wave which is followed by a spindle. Whether this response is a necessary or sufficient condition for behavioral inhibition has not been fully ascertained, although results of chemical stimulation indicate that behavioral inhibition need not necessarily be accompanied by unit inhibition and spindling. Novel afferent stimulation disinhibits the inhibitory effects of caudate or thalamic stimulation. Under certain conditions, detailed in the text, a disinhibitory stimulus can act as an inhibitor and an inhibitory stimulus can act as a disinhibitor.

Intracellular study of lemniscal and non-specific synaptic interactions in thalamic ventrobasal neurons

The effects of low frequency repetitive stimulation of medial thalamic (MTh) non-specific nuclei have been examined in intracellular studies of neurons of the ventrobasal (VB) thalamic complex. VB relay cells identified by medial lemniscus (ML) stimulation were relatively uninfluenced during recruiting responses elicited by MTh stimulation. VB neurons exhibiting long latency EPSPs or IPSP-EPSP sequences in response to ML stimulation were more consistently affected by MTh stimulation. Interactions observed in these elements were characteristically inhibitory in nature although in some cells facilitation of discharge without significant change in membrane potential occurred during MTh stimulation. Potentiation or enhancement of ML evoked IPSPs was observed in a small proportion of identified VB relay cells during 3nd as an after-effect of MTh stimulation. Spontaneosly developing 6–12/sec spindle waves in posterior sigmoid gyrus were associated with prominent IPSP and EPSP-IPSP sequences in VB relay cells. Stimulation of posterior sigmoid gyrus, corona radiata or internal capsule elicited prominent, variable latency, IPSPs or EPSP-IPSP sequences in relay cells and other neurons of the VB complex. The characteristics of these PSPs suggest the operation of complex interneuronal systems acting on VB relay cells via corticofugal projections. The intracellular data indicate marked differences in the distribution of synaptic pathways to VB relay and non-relay cells from medial non-specific nuclei. These results are considered in the light of previous findings on the effects of medial thalamic stimulation on specific neurons of the ventrolateral thalamic nucleus.

Intracellular potentials from “idle” cells in cerebral cortex of cat

Intracellular recording was carried out in “idle” cells from somatosensory, motor and anterior suprasylvian cortex of cat. The cells were studied simultaneously with examination of the DCR, spreading cortical depression, responses to stimulation of midline and postero-ventral thalamic nuclei, and Metrazol-induced seizure discharge. 1. 1. Observations were made on 70 cells showing resting membrane potentials of 50–80 mV. “Idle” cells show no injury discharge upon impalement and no spontaneous firing. During repetitively evoked DCR, and responses to repetitive stimulation (6–60/sec) of midline and postero-ventral thalamic nuclei, “idle” cells show a slow depolarizing response (SDR). The depolarization can attain a magnitude of 20 mV, summates and outlasts the stimulus period for one or more sec. The SDR never gives rise to cell discharge and closely corresponds in configuration to the evoked surface-negative shifts. If stimulation fails to evoke surface slow negativity, it produces no change in the intracellular record. 2. 2. During spreading cortical depression, a marked membrane depolarization (20–40 mV) occurs. Duration and configuration of the depolarization approximates the negative SP shift that accompanies the depression. During this sustained depolarization, a surface stimulus is no longer capable of producing an SDR. Upon recovery of resting membrane potential, surface stimulation once again evokes an SDR. 3. 3. After i.v. injection of Metrazol, there is a reduction in membrane potential followed by appearance of transient membrane depolarizations. Each depolarization corresponds closely to a paroxysmal wave recorded at the surface. 4. 4. The alternatives that “idle” cells are neuroglia, pyramidal cell dendrites or short axon cells are discussed.

Stable changes in the pattern of the recruiting response associated with a well established conditioned reflex

1. 1. Low frequency stimulation of midline thalamic nuclei can be used as a conditional stimulus in the elaboration of motor food procuring reflexes in cats which have been trained to take meat from a rack with the right forelimb. 2. 2. The food procuring conditioned reflex to stimulation of midline thalamic nuclei is elaborated after 50–70, and established after 100–200, trials in different animals. 3. 3. When the conditioned reflex is established at the point of cortical representation of the right forelimb (g. sigm. post. lat.) the recruiting response (RR) acquires a complex pattern composed of 3 surface negative waves: the preliminary one with a somewhat increased amplitude compared to its original size, the main RR component decreased in amplitude, and the subsequent newly formed wave, dominating in this complex by both its amplitude and duration. In the region of g. sigm. ant. RR are recorded unchanged compared to their initial pattern. 4. 4. The complex RR pattern formed at the poiny of cortical representation of the right forelimb after establishment of the conditioned reflex is extremely stable. It occurs in response to each application of the conditional stimulus during the whole existence of the given conditioned reflex. When the conditioned reflex is well established a similar additional surface negative wave is also recorded following the primary response elicited by electrical stimulation of the skin of the right forelimb.

Single unit studies on ventrolateral nucleus of the thalamus in cat: its relation to the cerebellum, motor cortex and basal ganglia.

Extracellular recordings were made from single neurons in cat's ventrolateral nucleus (VL) of the thalamus to study the mode of their activity as relay neurons mediating cerebellar impulses to the cerebral cortex. The following results were obtained.1. 144 VL units were recorded which fired with a short latency to brachium conjunctivum stimulation. Latencies ranged from 1.2 to 4.6 msec and the greatest number was between 1.5 and 2.0 msec. These units were presumably excited monosynaptically.2. 68 out of 144 VL neurons could be driven antidromically by a stimulus to the pericruciate cortex. Lowest threshold points for the antidromic activation were predominantly distributed on the precruciate gyrus3. Cortical stimulation also produced a prolonged inhibition of VL neurons, which may be attributed to recurrent inhibition. The inhibition was demonstrated after chronic ablation of the cortical gray matter.4. 21 out of 144 VL neurons were activated synaptically by pericruciate cortex stimulation, suggesting the existence of corticofugal facilitatory projection to VL.5. Globus pallidus and caudate nucleus stimulation usually had a facilitatory effect on VL neurons with occasional evoked discharges.6. Stimulation of nonspecific thalamic nuclei produced discharges of VL neurons followed by a prolonged inhibition.7. Functional relationships between VL relay neurons and the motor cortex were discussed and the role of VL neurons as the specific relay neuron was analized.

The recruiting response mechanism used as a conditional stimulus for the elaboration of the defensive conditioned reflex

1. 1. Low frequency stimulation of midline thalamic nuclei can be used as a conditional stimulus in the elaboration of defensive conditioned reflexes in dogs. 2. 2. A conditioned reflex formed to stimulation of midline thalamic nuclei differs from classical conditioned reflexes in remaining very labile and in requiring a greater number of trials for its establishment. 3. 3. Certain changes are observed in recruiting response (RR) characteristics during conditioning, which consist in: (a) development and subsequent increase in the amplitude of the additional positive RR component; (b) an increase in the amplitude of the initial positive RR component; (c) decrease of the main negative RR component. These changes in the amplitudes of additional RR components are most evident at the phase directly preceding the manifestation of the conditioned reflex. During extinction of the conditioned reflex a considerable amplitude decrease of all the RR components is observed.

Functional properties of synaptic pathways influencing transmission in the specific cerebello-thalamocortical projection system

Effects of stimulation of midline thalamic nuclei, caudate nucleus and reticular formation on responses evoked in n. ventralis lateralis by brachium conjunctivum stimulation have been studied to further elucidate the properties of synaptic pathways influencing input-output relations in n. ventralis lateralis. Low-frequency midline thalamic or caudate stimulation produces early facilitation and later developing inhibition of brachium conjunctivum-evoked responses in n. ventralis lateralis. These effects in n. ventralis lateralis are associated with diphasic negative-positive, focal potentials which are fundamentally similar in overt characteristics. Caudate evoked responses in n. ventralis lateralis have a longer latency and are more temporally dispersed than those elicited by midline thalamic stimulation. Inhibitory interactions between midline thalamic and brachium conjunctivum-evoked activities in n. ventralis lateralis are abolished by high-frequency caudate stimulation. The caudate-induced blockade of inhibitory interactions in n. ventralis lateralis is similar in many respects to that observed following high-frequency brain stem reticular formation stimulation. However, additional effects of reticular stimulation are seen in facilitation of brachium conjunctivum-evoked responses in n. ventralis lateralis, motor cortex and corticospinal tract. Motor cortex stimulation elicits a focal positivity in n. ventralis lateralis which is associated with inhibition of brachium conjunctivum-evoked activity. This inhibition mediated by corticofugal projections is not preceded by a phase of facilitation as in the case of midline thalamic or caudate stimulation. The results indicate that transmission of activity in cerebellothalamocortical projections may be dramatically influenced in n. ventralis lateralis by inhibitory and excitatory drives in intrathalamic, striothalamic and reticulothalamic synaptic pathways. Involvement of these synaptic pathways is considered in the genesis of movement disorders and the clinical effects of n. ventralis lateralis lesions in the treatment of dyskinesias.

Gegenseitige Beeinflussung von postsynaptischen Potentialen corticaler Nervenzellen nach Reizen in unspezifischen und spezifischen Kernen des Thalamus

1. The effect of non-specific excitation by medial thalamic (MT) electrical stimulation on PSP's of single nerve cells of the motor cortex elicited by electrical stimulation of specific thalamic nuclei (VL and VPL) was investigated. 2. If the VL-EPSP fell on the rising phase of the MT-EPSP (stimulus intervals of 5–40 msec) the latter added to the momentary depolarization resulting in facilitation of firing. If, however, the VL-EPSP was placed on the repolarizing phase of the MT-EPSP (30–80 msec) a significant reduction in amplitude was observed. This was true for primary as well as for secondary VL-EPSP at stimulation frequencies between 0.5 and 8/sec. VL-IPSP are enhanced during the MT-EPSP, mainly during its falling phase. Here even the absolute polarization of the IPSP could be increased. MT-EPSP were strongly reduced or even suppressed during the VL-IPSP, especially during its beginning. 3. The possible mechanisms of interaction within the thalamus and cortex were discussed. Although intrathalamic interaction and cortical presynaptic inhibition could not be ruled out completely, these mechanisms were considered insufficient to explain all observed phenomena. Therefore, an explanation was proposed assuming subsynaptic mechanisms in the receptive neurones themselves involving excitability changes of subsynaptic membranes.

Electrophysiological studies on the functional relationship between the nonspecific thalamic nuclei and the cerebellum in dogs

Some of the functional relationships between the nonspecific thalamic nuclei and the cerebellum have been investigated in dogs. The non-specific thalamic nuclei were stimulated and cerebellar responses recorded from the anterior lobe, the vermis, and the cerebellar hemispheres. 1. 1. Low frequency (7.5/sec) repetitive stimulation of nonspecific thalamic nuclei evoked biphasic (positive-negative) deflections in the anterior lobe, both hemispheres and the vermis. These potentials were grouped into three types according to their latencies and wave forms: type I of short latency, type II of long latency, and type III of double positive deflections in which the amplitude of the second positive deflection was always greater than that of the first. Type I was divided into two subtypes according to the duration (short, Ia; long, Ib) of the positive component; type II was divided into three subtypes according to the duration (short, IIa; long, IIb) and the latency (longest latency, IIc) of the positive deflection. Cerebellar responses evoked by stimulation of CM belong to the longest latency type (IIc), those evoked by stimulation of CL, Pc, and Pf belong to the long latency type (IIa, IIb), and those evoked by stimulation of SG and R to the short latency type (Ia, Ib). On the other hand, the latency of the cerebellar responses evoked by stimulation of primary and secondary afferent relay nuclei of specific thalamic system (VPL, VPM, VL) was shorter than that of the responses evoked by stimulation of nonspecific intralaminar thalamic nuclei and CM, and the responses could be observed primarily in the hemisphere on the side opposite to the stimulated thalamus. When MD and LP, which belong to association nuclei, were stimulated, their latencies were similar to those of nonspecific thalamic stimulation. 2. 2. High frequency repetitive stimulation (90/sec) of nonspecific thalamic nuclei induced low voltage fast patterns in the cerebral corticogram, but only elicited inconspicuous activation patterns in the cerebellogram. 3. 3. Low frequency stimulation of the nonspecific thalamic nuclei facilities the cerebellar response to subsequent subliminal stimulation of the sciatic nerve. These observations suggest that low frequency repetitive stimulation of the nonspecific thalamic nuclei may influence cerebellocortical activity as well as cerebrocortical activity.

Forebrain inhibitory mechanisms: Conditioning of basal forebrain induced EEG synchronization and sleep

There is evidence suggesting that EEG synchronization and sleep are capable of becoming associated with specific sensory stimuli through the process of conditioning. In some preliminary experiments it was found that the EEG and behavioral patterns induced by basal forebrain stimulation could be evoked by a tone which had been paired in time with electrical stimulation of this area in the cat. The present experiments are concerned with a closer examination of this conditioning. Adult cats were surgically prepared for chronic study with stimulating electrodes lowered bilaterally into the basal forebrain synchronizing area and the intralaminar thalamic nuclei with recording electrodes placed diffusely in the calvarium over the cerebral cortex. After recovery, these animals were placed in an observation chamber and presented with a fixed interval conditioning sequence of tone followed by basal forebrain stimulation. A conditioned EEG synchronization accompanied by behavioral manifestations of sleep developed rapidly to the tone when either low- (5 cycle/sec) or high- (150 cycle/sec) frequency stimulation in the basal forebrain was used as the unconditioned stimulus. Generalization of the conditioned response was observed when tone frequencies were changed, and discrimination developed in relation to a different tone paired with high-frequency (alerting) stimulation of intralaminar thalamic nuclei. A relationship between the frequency of basal forebrain stimulation and that of the conditioned EEG synchronization was also observed. These findings support the conclusion that important functional connections exist between the basal forebrain synchronizing areas and the cerebral cortex.

Effects of stimulation of cerebellar and thalamic nuclei upon spinal alpha motoneurons of the cat.

1. Effects of stimulation of cerebellar and thalamic nuclei on the spinal function were tested by recording monosynaptic reflex discharges from ventral roots and recording intracellular potentials from alpha motoneurons in the lumbar segments of the cat.2. The effect elicited by single pulse stimulation of nuclei was fairly the same between the animals under very light anesthesia and good general conditions. However, it was easily variable with a slight change of the animal conditions.3. Single stimulation of the fastigial nucleus (FN) elicited two group facilitations upon the monosynaptic reflex set up by tibial nerve stimulation (extensor), the one at a latency of about 10msec with a relatively short lapse and the other at a latency of 20-30msec with a long-lasting slow time course of 50-100msec. The facilitations appeared on bilateral bodily sides but more marked on the ipsilateral side than the contralateral. Scarce effect was observed with the FN stimulation upon the reflex set up by peroneal nerve stimulation (flexor).4. Single stimulation of the interpositus nucleus (IN) produced the reciprocal effect that was facilitatory upon the ipsilateral flexor reflex at a latency of 10-15msec while inhibitory upon the ipsilateral extensor reflex at a latency of about 15msec. Somewhat similar but undistinguishable effect was elicited upon the contralateral side.5. The effect of stimulating the dentate nucleus (DN) was characterized by the long-lasting slow facilitation upon bilateral peroneal and tibial reflexes. The facilitation appeared usually at a latency of 50-100msec and continued for about 100msec or more. It was often preceded by the other facilitation of a short latency of 10-15msec and of a relatively short duration.6. Single stimulation of the ventral-lateral nucleus of the thalamus (VL) elicited the facilitation upon bilateral peroneal and tibial reflexes at a latency of about 15 msec although far dominant upon the contralateral side. The time course of the facilitation showed an initial steep increase and a following slow decay. The lapse of the decay was always longer in the extensor reflex than the flexor one.7. Effects of repetitive stimulation of a nucleus were, in usual, deducible from the effect of single pulse stimulation of that nucleus as its temporal summation. However, they were rather complicated when compared with the single stimulation.8. The facilitation and inhibition of the monosynaptic reflex by stimulating cerebellar and thalamic nuclei seemed, in almost all cases, to be elicited by PSP mechanism in motoneurons which was produced directly or indirectly with descending impulses through spinal tracts.9. DN stimulation set up the inhibitory effect upon some motoneurons without any remarkable membrane potential change. Analyses of the effect showed, however, that the inhibition may be due to the shunting effect of the motoneuronal membrane by both EPSP's and IPSP's which converged to the motoneuron with a balancing amount and were neutralized mutually at the resting potential level.10. Most of PSP's in motoneurons elicited by the cerebellar and thalamic stimulation, especially the late group PSP's, were consisted of both EPSP's and IPSP's. Facilitation or inhibition of the motoneurons by the stimulation was the net result of the both PSP's.

The inhibitory action of the caudate nucleus in cortical primary receiving areas in the cat

1. I. The caudate nucleus repetitive stimulation (40–100 c/sec, 3 msec) effects on the thalamocortical evoked potentials, in primary receiving areas, were investigated in cerveau isolé or RF lesioned (electrolytic) animals (cats). 1. (a) The visual evoked potential (in gyrus marginalis) elicited by optic radiations, lateral geniculate, optic tract or optic nerve stimulation, was depressed during caudate head stimulation. 2. (b) The auditive evoked potential (in gyrus ectosylvius, areas I, II and in area III, Tunturi) elicited by medial geniculate body stimulation, was depressed during caudate stimulation. 3. (c) The somesthetic evoked potential (along the cruciate sulcus), elicited by VPL stimulation, was depressed during caudate stimulation. 4. (d) The thalamic mid-line nuclei stimulation facilitates all the optic, acoustic and somesthetic evoked potentials, in the same animals in which caudate stimulation depresses them. 5. II. The ascendant caudate influences have been investigated also in animals under light barbiturate anesthesia, comparatively with RF lesioned animals. 6. (a) In this condition the caudate stimulation may sometimes give a double effect, facilitation during the first 1–3 sec, followed by inhibition (during the same stimulation). 7. (b) The stimulation pulse shape changing from rectangular to triangular, with intensities immediately over-threshold, suppresses the facilitatory phase, the inhibitory one persisting. 8. (c) In animals in which a particularly marked facilitation phase to caudate stimulation occurs, electrolytic lesion or trans-section of rostral mesencephalic RF suppresses it. In these conditions, an increase of caudate stimulation intensities gives only an inhibitory effect. 9. III. The inhibition of evoked potentials in the optic, acoustic and somesthetic areas obtained by caudate stimulation is compared with the facilitation of these same potentials, through unspecific thalamic nuclei stimulation and also with the facilitation obtained in Bremer-Stoupel's experiments by reticular stimulation, in order to demonstrate the diffuse ascendent inhibitory action of the caudate nucleus. The caudate activating-like effects obtained sometimes in light barbiturate anesthesia, appear to be mediated through the mesencephalic RF, since its lesion suppresses only this activating phase.

Cortical and subcortical electrical activity in experimental seizures induced by metrazol.

An electroencephalographic study has been made of both cortical and subcortical activity occurring in the brain of the cat during seizures produced by convulsive doses of metrazol and by auditory stimuli or direct stimulation of thalamic nuclei in the presence of subthreshold doses. The effect upon this activity of various lesions was also observed. The seizure induced by threshold doses of metrazol appeared, by every test, to be primary in the cerebral cortex and to radiate from it to deep structures. Prominent activity in the internal capsule, basis pedunculi, subthalamus and midbrain tegmentum appeared to represent discharge descending to motor outflows. The basal ganglin did not display conspicuous seizure activity. The thalamus was prominently involved, its sensory relay nuclei exhibiting the most marked seizure discharge, paralleling that in related cortical areas. Associational thalamic nuclei were next most affected. The nuclei of the diffuse thalamic projection system were implicated later than their neighbors and manifested a markedly different type of activity, resembling giant spindle bursts. The possibility is suggested that this may be associated with loss of consciousness in seizures. With subconvulsive doses of metrazol, repetitive afferent stimulation led to development of a complex evoked potential in the receiving cortex, to its irradiation to other cortical area and, finally, to seizure induction. This series of events could still be provoked after destruction of the thalamus, except for the relay nucleus of the sensory pathway involved. It could be reproduced by direct stimulation of the thalamic sensory relay nuclei, but not the nuclei of the diffuse thalamic projection system. It was abolished by ablating the sensory receiving area of the cortex. The ascending sensory pathway and the cerebral cortex itself seem to be the only structures essentially involved in such seizure induction.