Search

Somatosensory evoked potentials (SEPs) to electrical stimulation of the right or left median nerve were studied in 4 patients with hemianesthesia and a severe thalamic or suprathalamic vascular lesion on one side. The SEPs were recorded with a non-cephalic reference. The normal side of each patient served as his or her own control. The lesion consistently abolished the parietal N20-P27-P45 and the prerolandic P22-N30 SEP components. It did not significantly affect the P9-P11-P14 positive far fields, nor the widespread bilateral N18 SEP component. This allowed N18 features to be studied without interference from cortical components. It is proposed that N18 reflects several deeply located generators in brain stem and/or thalamus whereas N20 represents the earliest cortical response of the contralateral post- central receiving areas., info:eu-repo/semantics/published

A computer program has been developed to analyze the neuronal signals in the cerebello-thalamo-cortical pathway. The mathematical constants in an equation capable of approximating cortical responses were systematically altered by the program in the calculation of theoretical cortical values. Using the correlation coefficient between the computer-generated and the experimentally produced cortical responses to the same thalamic signal, as evoked by a cerebellar stimulation, the effects of varying these constants can be determined. As these constants bear physiological meanings, the connections between the cerebellum, thalamus, and motor cortex, believed to play an important role in voluntary movements, can be studied in simulated, normal, and abnormal situations by introducing different values of these parameters into the program.

Retrogradely labeled thalamic neurons—the sources of afferents in the focus of peak activity induced by radial nerve stimulation—were investigated in adult cats by means of microiontophoretic horseradish peroxidase injection into the first somatosensory zone of the cerebral cortex. Labeled cells were found mainly in the ventroposterolateral and a smaller proportion in the posteroventral medial thalamic nuclei. Labeled neurons were distributed in groups differing in their morphological parameters within these nuclei.

Localizations of thalamic relay neurons of vibrissae, common fur of the muzzle and head, as well as those projecting to the cortical vibrissal field in mice with vibrissae coagulated at birth, have been studied by retrograde transport of peroxydase. The tracer was injected in the corresponding cortical areas. In coagulated mice, labeled thalamic neurons were situated in the ventro-basal complex anterior to its vibrissa part, corresponding to the area labeled after intracortical injection of the muzzle and head fur area. These results indicate a reorganization in the origin of thalamo-cortical afferents in coagulated mice.

Stimulation of the dentate nucleus in the chronically implanted baboon elicits both movements restricted to a single joint and also complex movements of several body segments. The complex movements correspond to precise but stereotyped coordinating activity. Two types of data reveal that the cerebello-thalamo-cortical system is concerned in the elaboration of complex movements. (1) Examination of cortical, pyramidal and muscle response latencies shows that the message might be transmitted by this pathway. (2) The complex movement which is produced by stimulation of a site in the dentate nucleus is similar to the sum of movements induced by stimulation of each cortical point receiving excitatory projection from this particular dentate focus.

Summary 1. Changes in electrorortical activity of cats and dogs during hypothermia were studied. 2. The frequency of background potentials changed almost linearly with temperature, though there was appreciable lag of the increase in the frequency during rewarming, whereas the wave frequency of spontaneous barbiturate bursts was fairly preserved in the face of moderate hypothermia. 3. Repetitive after-discharges elicited by single volley applied to the thalamus could be seen during cooling of the animal until they disappeared a little before or shortly after the beginning of rewarming at a temperature of about 20°C., and they reappeared when the animal reached a temperature of about 30°C. during rewarming. 4. Evoked potentials as picked up from the cerebral cortex as primary response to thalamic stimulation persisted even in the extreme of hypothermia in these experiments. 5. The behavior of both the thalamo-cortical circuits and brain stem activating system against cooling and rewarming is discussed, and it is concluded from these results that the oligosynaptic pathways are more resistant to cold and anesthesia than the multiysnaptic systems.

Both anterograde and retrograde degeneration techniques were employed to investigate the cortical projections of the dorsal lateral geniculate, medial interlaminar and posterior nuclei of the thalamus

1. 1. The effect of various cortical ablations upon recruiting responses and spindle bursts in cats was studied in acute preparations immobilized with gallamine. 2. 2. Recruiting responses were induced by low frequency stimulation of the midline thalamic nuclear complex; spontaneous spindle bursts were produced by mesencephalic reticular formation lesions. 3. 3. Ablations of primary cortical areas (somato-sensory, auditory and visual), motor cortex and association areas, and orbito-frontal cortex were made in sequence and singly. Extensive ablations of the dorso-lateral convexity enhanced and modified both spindle bursts and recruiting responses. Only orbito-frontal cortex ablations abolished recruiting responses and spindle bursts recorded at the cortex, in the subcortical white matter, and in the thalamus. 4. 4. The results of these experiments suggest that the orbito-frontal cortex is an essential link in a thalamo-cortical synchronizing system responsible for spindle bursts and recruiting responses.

1. 1. During sleep characterized by a low voltage fast EEG, recruiting responses could be elicited in cats in the course of repetitive stimulation of “non-specific” thalamus by using a stimulus strength slightly supraliminal for recruiting responses during sleep characterized by EEG slow waves. 2. 2. The occurrence of recruiting responses and “sustained waves” depended on the stimulus strength and the actual state of the animal. 3. 3. In the same animal the thresholds for eliciting recruiting responses during slow wave sleep and “sustained waves” during low voltage fast sleep and quiet wakefulness were about the same. There was no remarkable difference between the latencies of the “sustained” and recruiting waves during low voltage fast sleep. 4. 4. During low voltage fast sleep, recruiting responses and rapid eye movements (REMs) usually did not appear simultaneously; i.e. , if stimulation was started during REMs the first recruiting response was often delayed. From another point of view, REMs did not usually start during recruiting responses. A similar relationship was found between recruiting responses and the electrical activity of the levator palpebrae superioris muscles. The decrease of the tonic component of the levator EMG was often parallel with the waxing phase of the recruiting response. In the waking state also the searching eye movements and recruiting responses did not usually occur concurrently. 5. 5. It can be assumed that during low voltage fast sleep in the course of continual repetitive stimulation, the temporal distribution of recruiting response groups corresponds to fluctuations of the low voltage fast sleep level. These fluctuations might indicate an occasional tendency to slow wave sleep.

Cortical responses evoked by afferent stimulation of the visual pathway have been observed during increased gravitational stress simulated by a centrifuge. An enhancement of the responses is observed during positive (long axis) acceleration and is related to the magnitude and duration of the linear acceleration. It is not induced by angular accelerations and does not occur during lateral acceleration. It is concluded that the hypotension induced by positive acceleration is essential to the changes in thalamo-cortical excitability. The phenomenon arises from reduced cerebral blood flow but the central effect of carotid receptor activity may be involved. The effects are unlikely to be mediated by the reticular formation but probably arise from changes in cellular excitability induced directly at thalamic and cortical levels. It is suggested that in the conscious animal the increased sensory inflow of gravitational stress may also modify thalamo-cortical excitability, and under these circumstances the effects of increased gravitational stress may modify both reticular and forebrain mechanisms.

Both anterograde and retrograde degeneration techniques were employed to investigate the cortical projections of the dorsal lateral geniculate, medial interlaminar and posterior nuclei of the thalamus

Bei Reizung des Kaninchenauges mit energiegleichen Lichtern verschiedener Spektralbereiche zeigte sich, das nur mit Rotlicht λmax 641 mμ kein Elektroretinogramm und keine spezifischen Aktionspotentiale des Corpus geniculatum laterale und der Sehrinde abzuleiten sind.

The Rorschach form-perception test was used preoperatively and postoperatively, whenever conditions permitted, in a series of 20 psychotic patients subjected to therapeutic bilateral prefrontal lobotomy. A continuing clinical followup was made on each patient for periods ranging up to one year. Because of the severe psychotic subjects with whom we were dealing, and other factors tending to reduce the number of cases available for reliable comparative studies, it was not possible to compute quantitative relationships on the basis of age, sex, or diagnosis. Qualitatively, the study revealed that the changes from preoperative records to postoperative records are not very large, in most cases, and that atypical signs present in the postoperative records are frequently anticipated in the preoperative records. In the postlobotomy course, Rorschach improvement may, or may not, run parallel with clinical improvement. An analysis of the postoperative scoring signs revealed the presence of several of Piotrowski’s criteria of intracranial damage, but since they frequently appeared in the preoperative picture, it was felt that they were more a function of the psychotic processes than of the lobotomy. In general, it appears that the neurosurgical transection of the frontal association areas plays a less important role in the reorganization of the Rorschach patterns than does the prepsychotic and preoperative personality structure.

Cortical incremental responses to repetitive thalamic stimulation were studied in normal and protein malnourished rats. The rate of cortical incrementation ipsilateral to the thalamic site of stimulation varied as a function of stimulus repetition rate but was unaffected by dietary treatment. The waveform of the ipsilateral response likewise was unaffected by protein malnutrition and a characteristic positive-negative-positive response was observed. In the cortex contralateral to thalamic stimulation, seven of eight malnourished animals exhibited a surface positive peak, in some cases quite prominent, at a latency at which seven of eight normals exhibited a prominent surface negativity. These results are discussed in relation to reported effects of malnutrition on sensory evoked potentials.

Neurons displaying a thalamo-cortical projection were marked by means of the retrograde transport of horseradish peroxidase (HRP), and the labeled elements were compared with neurons impregnated by the Golgi technique. Injections of HRP into the posterior area of the limbic cortex resulted in its uptake by various anterior thalamic nuclei, especially the anteroventral nucleus. HRP-positive cells are characterized by their position, dendritic orientation, and the shape and size of their somata. On the basis of the combined HRP- and Golgi-analysis three different types of thalamo-cortical relay neurons can be distinguished.

Publisher Summary This chapter addresses two questions related to the circuitry of the visual cortex on the basis of Golgi observations. The first is: What types of neurons with intracortical axons can be contacted by geniculo-cortical fibers? The second is: How are these fibers three-dimensionally arranged in layer IV of the primary visual cortex? The Golgi method is used to study the forms of nonpyramidal cells in the primary visual cortex in three animal species; neuronal types that could be the recipients of the geniculo-cortical input are sought. These neurons are classed according to dendritic and axonal characteristics, into several distinct groups: spine-free neurons with either generalized or specialized axons, and spiny neurons always bearing axons of the generalized type. Specific afferent fibers are identified in Golgi preparations, and their geometrical properties are analyzed by means of computer rotations. The morphology differs in the animal species studied, but some basic properties are maintained. Except for laminar distribution, no definite patterns of arborization are found in mouse and monkey, whereas, in cat, afferent fibers form discrete preterminal arborizations.

The thalamo-cortical relationships of alpha rhythms have been analysed in dogs using partial coherence function analysis. The objective was to clarify how far the large intracortical coherence commonly recorded between different cortical sites could depend on a common thalamic site. It was found that the alpha rhythms of the LGN influenced only moderately the coherence between cortical alpha rhythms whereas that of the pulvinar had much more influence, at least in relation to some cortical areas. Significant phase shifts between thalamus and cortex were also measured. The results demonstrate that there are thalamo-cortical and cortico-cortical components which interact in the generation of cortical alpha rhythms.

The organization of thalamic afferents to the rat's visual cortex was investigated autoradiographically and through the retrograde transport of horseradish peroxidase (HRP) following injections into striate and peristriate cortex. The results revealed that Nucleus lateralis posterior (NLP) projects to a large peristriate cortical field that includes areas 18A, 7, and the anterior portion of area 18, and to a circumscribed temporal area corresponding to Krieg's ('46a,b) area 20. The dorsal lateral geniculate nucleus (LGNd) was shown to project to two spatially discontinuous cortical areas. The largest geniculate receiving area is partially coextensive with Krieg's area 17, but an extension of this projection posterior and medial to the striate cortex was found. In addition, a geniculate projection to a restricted field located in the lateral peristriate cortex was identified. Concurrent investigations were designed to assess the pattern discrimination abilities of rats prepared with striate cortical ablations, lesions in NLP and combined striate-cortical and thalamic ablations. Comparison of these animals with normal control subjects revealed that the striate cortex in the rat (as in the cat [Doty, '71; Sprague et al., '77] and the tree shrew [Killackey and Diamond, '71; Ware et al., '74]) is not necessary for successful pattern discrimination, and that the geniculo-striate and NLP-extra-striate projection systems are both involved in mediating the visual discriminative abilities of the rat. The results add species generality to the concept that the central connections to the visual cortex are characterized by parallel-conducting thalamic channels and contribute to the growing number of demonstrations that the extra-striate cortex and associated thalamic cell groups contribute significantly to the process of visual-pattern recognition.

The thalamo-cortical neurons conveying impulses responsible for cortical recruiting and spindling activities were identified by a combined electrophysiological and anatomical method using horseradish peroxidase in cats. The neurons relating to the frontal motor cortex (areas 6 and 4) were found to be distributed mainly in the ventromedial part of the ventral anterior and ventral lateral nuclear complex of the thalamus. The neurons relating to the parietal association cortex (area 5) were seen to be localized chiefly in the dorsolateral part of the nuclear complex.

Twenty-five taste and 35 mechanoreceptive neurons were recorded from the parvicellular part of the posteromedial ventral nucleus (VPMpc) in rats. Among them, 14 (56%) of the taste and 7 (18.4%) of the mechanoreceptive neurons were antidromically activated from the cortical taste area (CTA) with a latency of 1–4 ms and identified as thalamocortical (TC) relay neurons. No significant differences were evident in the receptive field properties or in the location in the VPMpc between the TC and non-TC neuron groups. Two classes of TC neurons were recognized: one class consisted of neurons which were most excited by NaCl among the four basic taste stimuli with receptive fields (RFs) confined to a part of the oral cavity, e.g. the anterior tongue, and the other class contained neurons which were most excited by sucrose or HCl, with RFs over a wide area of the oral cavity. Both the TC and non-TC neurons showed similar effects of CTA stimulation: post-stimulus time histograms revealed a long lasting inhibition followed by a rebound facilitation of spontaneous discharge.

Three rhythmic cortical phenomena (rhythmic after-discharges, incremental responses and self-sustained after-discharges formed by spike-and-wave rhythm) were elicited by electrical stimulation of thalamic nuclei during ontogenesis in rats. All three phenomena could be recorded for the first time at the age of 12 days and they matured until the 18th postnatal day. Possible explanation for the delayed development of these rhythmic thalamo-cortical phenomena in comparison with single thalamo-cortical responses are discussed.

In 25 rhesus monkeys horseradish peroxidase was injected in different parts of the frontal cortex. The retrogradely labelled thalamic neurons formed longitudinal bands, some of which crossed the internal medullary lamina, and extended from one thalamic nucleus into another. On the basis of these findings the frontal cortex was subdivided into seven transverse cortical strips which receive afferents from seven longitudinal bands of thalamic neurons. The most rostral transverse strip receives afferents from the most medial thalamic band which is oriented vertically and extends through the most medial part of the MD into the medial pulvinar. Progressively more caudally located transverse strips receive afferents from progressively more laterally located thalamic bands which in part are situated in the VL and show an increasing tilt towards the horizontal. Moreover, those parts of the various bands which are situated along the dorsal and lateral margin of the thalamus project to the medial portions of the transverse cortical strips, i.e. along the medial margin of the frontal lobe, while the other parts situated ventromedially in the thalamus project to the lateral portions of these strips, i.e. along the lateral margin of the frontal lobe. These data provide an alternative view of the organization of the thalamus and suggest that this structure contains a matrix of longitudinal cell columns which in some cases extend across specific nuclear borders and may represent the basic thalamic building blocks in respect to the thalamo-cortical connexions.

Foci of excitation in the central nervous system which become dominant foci, hence yielding the same reflex response regardless of the place and type of stimulation, present a conceptual problem since a diffuse spread of excitation is present concurrently with a local excitatory condition. This, in turn, raises the question of the dynamic relations between the specific and nonspecific afferent systems.

Die Wirkung des Schlafdialysates des Kaninchens auf das Gehirn eines normalen Empfangers kennzeichnet sich durch Erregbarkeitszunahme des mediozentralen somnogenen thalamischen Feldes (Amplitudenzunahme der im Cortex ausgelosten Potentiale). Eine ahnliche Wirkung ubt Chlorpromazin als zentraldampfendes Pharmakon und Substanz P aus, wahrend zentrale Stimulantien wie Amphetamin eine umgekehrte Wirkung entfalten.

1. 1. The pathways of the non-specific thalamo-cortical projection system, in the cat, are independent of the specific thalamic nuclei and the striatum. 2. 2. The non-specific pathways pass forward to the oral pole of the thalamus where there is a topographical organization, with the ventro-medial portion related to anterior and the dorso-lateral portion to posterior cortical responses. 3. 3. The final neurons in this multi-synaptic thalamic pathway probably lie in the nucleus reticularis and pass in a topographical manner through the internal capsule directly to various cortical areas. 4. 4. Transcortical transmission was not found to be an important factor in the distribution of non-specific thalamo-cortical responses.

1. 1. Spontaneous alpha rhythms and barbiturate spindles have been recorded in dogs from the same electrode sites (thalamus and cortex). 2. 2. Alpha rhythms were found to differ from barbiturate spindles as regards their spectra and topographic distribution. 3. 3. Thalamo-cortical coherences obtained during alpha rhythm differed significantly from equivalent coherences during barbiturate spindles for many thalamic and cortical sites. The latter were larger than the former. 4. 4. It is concluded that thalamic and cortical sites act more independently of one another in the state in which alpha rhythms occur than under light barbiturate anaesthesia.

Arousal and activation in nonspecific reticulo- thalamo-cortical systems due to underlying emotion expressed through cortical, visceral and somatomotor channels

Publisher Summary This chapter focuses on the influence of pituitary-adrenocortical hormones on the thalamo-cortical and brain stem limbic circuits. The main connections of the brain stem and basal forebrain structures playing a role in the organization of motivated behavioral reactions are illustrated in the chapter. The ascending activatory system, through multisynaptic and oligosynaptic pathways, influences the forebrain, which is known to be involved in the organization of complex behavioral mechanisms and the regulation of pituitary functions. On the other hand, the descending inhibitory pathways of basal forebrain origin, terminating at both the thalamic and the brain stem level, play an important role in the control of sensory input. Recent observations clearly show that corticosteroids, like other steroids of gonadal sources, can modify the central nervous system at two different levels and in two different ways. The chapter discusses routes that may be involved in corticosteroid action on the central nervous processes besides the priority of a neuronal excitability state that basically determines the behavioral resultant of hormonal influence. The hormones may exert either a facilitatory or an inhibitory effect, and the behavioral outcome can be facilitation or inhibition, depending on the site of action. According to this assumption, opposite behavioral effects of corticosteroids may explain changes in mood and emotionality in human beings, as well as diverse behavioral manifestations in different species and ambivalent reactions or rebound-like phenomena in the same individual.

It is generally accepted that excessive synchronization (hypersynchrony) should be one of the essential features of epileptic activity in the nervous tissue (see e.g., Jasper 1969, Creutzfeldt 1969, and Ajmone Marsan 1969).