Association Thalamic Nuclei Research Articles

Distribution of afferents from thalamic association nuclei in the occipital and parietal cortex in cats

The laminar distribution of endings of thalamocortical fibers was studied in the parietal (area 7) and visual cortex (area 17) after ultrasonic destruction of the pulvinar, by the Fink-Heimer method and by electron microscopy. Degenerating fibers and their endings were found in the parietal cortex in all layers, with the greatest concentration in layers III–V. In the visual cortex fibers from the pulvinar terminate chiefly in layer IV. Degenerating fibers terminate on spines and thin branches of dendrites in both the parietal and the visual cortex.

Control of thalamic transmission by corticofugal and ascending reticular pathways in the visual system.

Control of thalamic transmission by corticofugal and ascending reticular pathways in the visual system.

Pathophysiology of generalized penicillin epilepsy in the cat: The role of cortical and subcortical structures. I. Systemic application of penicillin

The mechanism of precipitation of generalized epileptiform discharges in feline generalized penicillin epilepsy, a model of human generalized corticoreticular (‘centrencephalic’) epilepsy, was studied in acute and chronic experiments in cats with implanted skull and intracerebral electrodes. Single shock and low frequency repetitive stimulation of subcortical sites from which prior to penicillin administration spindle activity and recruiting responses could be elicited, readily triggered epileptiform discharges in the same animals after penicillin. These structures comprised the intralaminar and midline thalamic nuclei, the neostriatum, and some posterior thalamic association nuclei (Pulvinar and nucleus lateralis posterior). Subcortical and cortical structures which prior to penicillin elicited neither spindle activity nor recruiting responses were significantly less effective in triggering generalized epileptic bursts after penicillin injection. The probability with which such bursts were elicited from these structures was still, however, in many instances above chance level. It is concluded that the generalized epileptiform discharges in feline generalized penicillin epilepsy can be triggered from a large number of brain sites, but most reliably so from subcortical nuclei involved in spindle generation and recruiting responses. The experimental evidence presented still does not allow one to determine whether epileptic alteration of neuronal function in this form of epilepsy primarily resides in cortical or subcortical nerve cells or in both.

Topographic distribution of visual and somesthesic unitary responses in the Pul-LP complex of the cat

An electrophysiological analysis of field potentials and unitary responses evoked by visual, acoustic and somesthesic stimuli in thalamic associative nuclei was performed in ‘encéphale isolé’ cats. Photic responses were particularly pronounced in the pulvinar nucleus (Pul) including its inferior division, while in lateralis posterior (LP) and, to a lesser extent, in the posterior nuclear group (PO) a prevalence of somesthesic responses was found. Only a few units were influenced by the acoustic (clicks) stimulation. Unitary convergence and interaction was a characteristic common to all divisions of Pul-LP complex. Areas of different functional significance can therefore be traced into the associative thalamic posterior nuclei, according to their modal sensitivity. The topographic functional organization is in partial agreement with the distribution of afferent connections shown by previous anatomical studies.

An intracellular study of thalamocortical synapses in the orbito-insular cortex

Intracellular recordings were made in multimodal orbito-insular cortex in response to electrical stimulation of thalamic association nuclei. Four types of responses were observed: One was short latency excitation; another was short latency excitation followed by inhibition; the third was long latency inhibition followed by excitation; the fourth was rhythmic afterdischarge. The initial excitatory response is viewed as being due to direct thalamocortical input and the later inhibitory ones to intracortical inhibition. The results resemble those obtained in lemniscal systems having specific thalamic relay nuclei, and they provide correlates for recent anatomical reports concerning the projections of the frontal orbital cortex.

The human auditory evoked response and contingent negative variation in hyperbaric air

The auditory evoked response (AER) and contingent negative variation (CNV) were recorded from thirteen experienced divers, before, during and following an exposure to an increased ambient air pressure simulating a depth in sea water of 91.5 m (300 ft., 10 atm. abs.). Off-line data analysis was accomplished using a LINC 8 General Purpose Digital Computer. The results indicate that the AER was significantly affected at depth, as shown by an average 63.5% ± 4.5 reduction in the N 1P 2 amplitude, whilst the CNV showed no significant changes from controls. The results are interpreted as indicating that the AER and CNV are generated by independent mechanisms. The AER is considered to be attenuated by inhibition exerted during its propagation and passage through the ascending reticular activating system (ARAS). The CNV is considered to be a self propagating phenomenon, initiated by the interaction between the specific, non-specific and associational thalamic nuclei and, as such, to be at least partly independent of the changes assumed to occur in the activity of the ARAS.

The spread of after-discharge from stimulation of the rhinencephalon in the cat

1. 1. The spread of after-discharge following electrical stimulation of the dorsal and ventral hippocampus, septum, basal and lateral amygdaloid nuclei, and the anterior sigmoid gyrus has been studied in locally anesthetized cats and in animals anesthetized with Dial. 2. 2. From each stimulated focus after-discharge was found to spread diffusely to subcortical and paleocortical areas, but the overall epileptoid response varied in character and some areas remained negative. Propagation of after-discharge to the dorsolateral isocortex was less diffuse than that to subcortical brain levels. 3. 3. Following stimulation of each area investigated, rhythmic after-discharge of high amplitude was recorded from certain brain structures and these corresponded with the same areas that fired at liminal stimulation of the same foci in animals anesthetized with Dial. These were predominantly rhinencephalic and hypothalamic nuclei when rhinencephalic areas were stimulated and structures of the pyramidal and extrapyramidal systems when the anterior sigmoid gyrus was stimulated. 4. 4. The medial geniculate body, ventrolateral reticular formation and associational thalamic nuclei responded prominently to each of the rhinencephalic structures stimulated. 5. 5. After-discharge of certain areas appeared to be distinctive, such as: activation of the ventral thalamus following ventral hippocampal stimulation; the intralaminar thalamic nuclei after dorsal hippocampal stimulation; the sensorimotor cortex after basal amygdaloid stimulation; and superior colliculus and lateral geniculate nucleus after stimulation of the septum. 6. 6. It is concluded that each area stimulated has a pattern of ictal projection to the subcortex, paleo- and juxtallocortex and neocortex that is sufficiently distinctive, but that there is considerable overlap in the main projection areas of each rhinencephalic focus. There is a strong contrast between the propagation pattern of after-discharge from the rhinencephalon and that originating in the anterior sigmoid gyrus. 7. 7. The possible correlation of certain features of rhinencephalic after-discharge with autonomic and behavioral effects generally known to follow rhinencephalic stimulation or ablation, and with clinical effects of psychomotor epilepsy have been discussed.

Étude des systèmes ⪡ associatifs ⪢ visuels et auditifs chez le chat anesthésié au chloralose

1. 1. In cats deeply anesthetized with chloralose cortical responses to visual or auditory stimulations can be observed in the suprasylvian and lateral anterior gyri. These cortical “association” responses as well as the subcortical pathways upon which they depend were the object of the present study. 2. 2. The association areas occupy well-defined areas of the cortex (two visual areas and two auditory areas). The corresponding responses differ from the primary evoked potentials by their longer latency, their long duration and by their greater lability. 3. 3. The association responses do not depend upon the corresponding primary projection areas. This is clearly demonstrated by their persistence after removal of the primary projection areas and their resistence towards any experimental modification of the reactivity of the primary areas. 4. 4. Extensive destruction of the mesencephalic reticular formation does not abolish these responses. It seems therefore necessary to reject a hypothesis according to which the origin of the responses would be within the non-specific projection system. 5. 5. The organization of the thalamo-cortical pathways mediating these responses seems for each of the two sensory systems studied to depend upon “collateral” elements which detach themselves from the primary pathway and enter into thalamic association nuclei and hence the responses are conducted to the corresponding cortical areas. It has been shown indeed that stimulation of the primary relay nuclei (medial and lateral geniculate bodies) produces primary and associative responses. It has further been shown that responses to either visual or auditory stimuli can be recorded within the lateral-posterior nuclear group of the thalamus. For visual stimuli the thalamic association area occupies the nucleus posterior and the dorsal part of the nucleus lateralis posterior. For auditory stimuli the corresponding areas occupy the inferior part of the nucleus lateralis posterior and the nucleus suprageniculatus. Finally it has been shown that projection from these thalamic structures upon the suprasylvian cortex can be confirmed with localized thalamic stimulation. 6. 6. The significance of these results, especially the fact that experimentation under deep chloralose anesthesia permits to identify specific association systems, is discussed.

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.