Showing papers on "Somatosensory system published in 1976"

Visual cells in the pontine nuclei of the cat.

Abstract: Two hundred and thirty-two visually activated neurones were recorded in a small area of the rostral pontine nuclei of cats. The location of visually activated neurones was coextensive with the input from visual areas of cat's cortex as determined by degeneration studies. 2. Pontine visual cells could only be driven by visual stimuli. Cells responsive to somatosensory or auditory stimuli were also found in different regions in rostral pontine nuclei. They too responded to only one modality. 3. 96% of the cells were directionally selective. 4. Pontine visual cells were responsive to a wide range of stimulus speeds. Some cells responded to targets moving as fast as 1000 degrees/sec without losing directional selectivity. No pontine visual cells gave a clearly sustained response to a stationary stimulus. 5. Exact stimulus configurations were not critical. Large fields containing many spots were the most effective stimuli for 50% of the cells. Inhibition of responses depending upon stimulus dimensions, direction of movement, or location in the visual field was found for many cells. 6. Receptive field dimensions were large, ranging in size from 3 degrees X 4 degrees to more than an entire hemifield. 7. 94% of the cells had receptive fields which were centred in the contralateral hemifield. 8. 98% of the cells could be driven from both eyes. 9. The properties of the pontine visual cells suggest a corticopontocerebellar pathway sensitive to a wide range of speeds and directions of movement, but not sensitive to precise form.

Representation of vestibular afferents in somatosensory thalamic nuclei of the squirrel monkey (Saimiri sciureus).

Abstract: 1. In awake squirrel monkeys the thalamus was investigated for neuronal responses to vestibular, auditory, visual, proprioceptive, and exteroceptive somatosensory stimulation. The vestibular representation in the thalamus was focused.2. Units responding to electrical vestibular stimulation were found to be scattered within thalamic nuclei receiving somatosensory afferents.3. Ventrobasal neurons have previously been considered place and modality specific. The present data suggest exceptions to this belief. Vestibular input converges with somatotopically organized proprioceptive afferents on neurons in the nucleus ventralis posterior lateralis, pars oralis (identical to nucleus ventralis intermedius), as well as in the posterior portion of the caudal part of the same nucleus. Convergence of both modalities was also found in other nuclei, mainly belonging to the posterior nuclear group, where auditory convergence was also demonstrated.4. Of the vestibular cells in the nucleus ventralis posterior lateralis, 23% projected to the sensorimotor cortex, some with collaterals to both pre- and postcentral gyri.

The role of sensory innervation in the development of mechanoreceptors.

Abstract: Publisher Summary The essential component of peripheral receptors is the sensory nerve terminal of the primary sensory neuron. The sensory neuron is polarized in order to receive messages at the periphery, and then transmitted to the nerve centers. However, the sensory neuron may also act in the reverse direction, inducing the differentiation and ensuring the maintenance of specialized cells constituting the peripheral receptor. Such a neural effect of sensory terminals upon specialized cells is observed in various types of receptors, both primary and secondary. Sensory nerve terminals apparently induce and maintain the differentiation of nonnervous components of muscle receptors and Pacinian corpuscles of the rat. The development of muscle spindles, Golgi tendon organs, and Pacinian corpuscles is arrested after neonatal neurotomy, and the immature receptors disintegrate within 10 days after denervation. On the other hand, rat muscle spindles continue to develop and differentiate ultrastructurally after neonatal de-efferentation, if their sensory innervation remains preserved.

Astereognosis. Tactile discrimination after localized hemispheric lesions in man.

Abstract: • The specific object of this study was to determine which cortical areas have to be damaged or disconnected to cause an impairment of somatosensory discrimination (astereognosis). Ninety-three patients with verified unilateral and circumscribed lesions took part in a somatosensory two-alternative forced-choice discrimination of size and shape. The results failed to support earlier views of astereognosis. Only direct damage to or an undercutting of the anterior part of the middle third of the postcentral gyrus caused impairment of size and shape discrimination (astereognosis) contralateral to the lesion. When the hand is used for stereognostic discrimination, the integration of somatosensory impluse patterns into spatial information about the objects is believed to take place in the contralateral somatosensory hand area.

Descending influences of periaqueductal gray matter and somatosensory cerebral cortex on neurones in trigeminal brain stem nuclei.

Abstract: Single relay (to thalamus) and nonrelay neurones that responded to innocuous and/or noxious oral–facial stimuli were located in trigeminal brain stem nuclei oralis and caudalis. The responses of th...

Effects of Dorsal Fornix Section and Hippocampectomy on Adrenocortical Responses to Sensory Stimulation in the Rat

Abstract: With the purpose of identifying the neural structures which are involved in the mediation of the adrenocortical responses to photic, acoustic and sciatic nerve stimulation, experiments were conducted on male rats with bilateral section of the dorsal fornix and dorsal or ventral hippocampectomies. The basal corticosterone levels in these animals were not significantly different from those in controls. Stimulation of the 3 sensory modalities produced normal adrenocortical responses in rats with fornix section. The hippocampectomies had no effect or only a marginal effect on the response to ether stress and to photic and acoustic stimulation; however, the adrenal response to sciatic stimulation was very significantly reduced. The data demonstrate the participation of the hippocampus in the transmission of somatosensory responses which promote adrenocortical activity. The efferent connections of the hippocampus to the hypothalamus which are involved in this mechanism are discussed.

Effects of serial lesions of somatosensory cortex and further neodecortication on retention of a rough-smooth discrimination in rats.

Abstract: Five groups of rats with bilateral lesions of the somatosensory cortex and one of animals sustaining only sham operations were tested for retention of a rough-smooth discrimination. Two of the lesion groups had sequential unilateral ablations, in one case with interoperative testing, and three groups had one-stage bilateral lesions. The two groups of animals with serial lesions did not differ from each other or from sham operates in relearning the task. Rats with one-stage lesions and preoperative overtraining also performed well, but the other one-stage groups showed deficits relative to control and serial lesion groups. In the second experiment the sham operated rats from Experiment 1 experienced lesions anterior and posterior to the somatosensory zones. These lesions did not affect retention. Somatosensory cortex then was ablated in one operation and severe performance decrements were seen. Removal of additional neocortex in a sample of animals that had relearned the discrimination after one-stage somatosensory cortex lesions (Exp. 1) also affected retention. In contrast, retention was not impaired on some of the measures in those animals that originally had two-stage ablations. The findings from these two experiments show that some ablation effects can be circumvented with overtraining or serial lesion techniques. The data also indicate that non-somatosensory cortex may play a role in recovery after somatic cortex lesions, but that the substrates underlying recovery might, not be the same after one-stage and two-stage ablations.

Effects of multifocal brain stimulation on pain and somatosensory functions

Abstract: Publisher Summary This chapter presents a study examining effects of multifocal brain stimulation on pain and somatosensory functions. The stimulating electrodes for temporary implantation were designed similarly to those used by others both in experimental animal work and in patients. The electrode material was originally steel, and was later exchanged for gold or platinum to minimize the possible deposition of toxic metal ions during stimulation. The diameter of the electrode wires was 0.1 mm, and four or six wires were twisted together so that the overall dimension of the composite electrode amounted to 0.4 mm. The distance between the stimulating points was about 4 mm. It was observed that stimulation within the sensory nuclei of the thalamus (VPM, VPL) and within the posterior limb of the internal capsule regularly produced paresthesias. The thresholds were found to vary considerably in different locations of one and the same structure. In one of the patients with pain of central origin, there was a tendency to a spontaneous decrease of the thresholds for paresthesias during the course of stimulation. The results of this study confirmed that stimulation of the thalamic sensory nucleus (VPM) can alleviate facial pain (anesthesia dolorosa).

Somatosensory cortical involvement in responses to noxious stimulation in the cat : Exp. Brain Res., 20 (1974) 363–374

Abstract: s These abstracts have been selected and written by the Editorial Panel Leaders.

Sensory Jacksonian seizures.

Abstract: Sensory Jacksonian seizures were analyzed in 42 patients with regard to anatomical and temporal sequences. The origin of sensory Jacksonian seizures, in contrast to motor Jacksonian seizures, often began at peripheral sites with littel cortical representation. The progression of seizure activity across the cerebral cortex followed a course that was neither rectilinear, radiate, nor random; it appeared to preceed in an organized manner to involve functionally coherent units. The patterns analyzed conformed more closely to cortical somatosensory maps reported for the chimpanzee than the sensory sequences presently available for the cortex of man. Complete diagnostic studies are indicated in patients presenting with sensory Jacksonian seizures because of the frequency of related focal pathology.

Direct action of angiotensin II on central neurons

Abstract: Response of nerve cells of the somatosensory and visual cortex and anterior hypothalamus of rabbits and also of the isolated circumesophageal nerve ring ofHelix pomatia to microiontophoretic administration of angiotensin II (A-II) were studied Responses of the rabbit brain neurons to A-II were characterized by a marked increase in the frequency of spike discharges which depended on the dose of the drug injected Neurons of the anterior hypothalamus had a lower threshold of response than cortical neurons Application of A-II to the soma of the recorded snail cells caused a marked but reversible decrease in the membrane potential level The resistance of the membrane under these circumstances was reduced by two to four times These results are evidence of the direct action of A-II on central neurons

Vestibulo-thalamic projections studied with antidromic technique in the cat.

Abstract: The vestibulo-thalamic projection was investigated in anaesthetized cats. Electrical stimulation of posterolateral thalamic areas frequently changed the spontaneous firing pattern of neurons in the vestibular nuclei but only 5 % were antidromically invaded. This group was further analysed with regard to types of labyrinthine and somatosensory input; thalamo-projecting neurons in the vestibular nuclei are frequently located in the lateral vestibular nucleus, they receive no monosynaptic inflow from the labyrinth and they often receive convergent vestibular and somatosensory input.

Evoked potential studies in neurological disorders.

Abstract: Techniques for recording and analysing visual and somatosensory evoked reponses using an on-line PDP 11/40 computer have been developed and applied to a group of subjects with established or suspected multiple sclerosis as well as to patients with a variety of other lesions of the visual pathways, myoclonic epilepsy and functional neurological deficits. The most consistent responses were obtained using the pattern reversal visual evoked response and the spinal somatosensory evoked response, abnormal responses being found with both techniques in a significant number of patients with suspected demyelinating disease even in the absence of symptoms or signs referable to the visual or somatosensory pathways. The complementary role of these techniques in the detection of sub-clinical abnormalities of conduction in sensory pathways in patients with suspected MS is emphasized.

Comparative electrophysiological characteristics of afferent representation in the cortical and striatal divisions of the turtle forebrain

Abstract: In experiments on immobilized, lightly anesthetized turtles the presence of visual and somatic representation was established in the subcortical striatal division of the forebrain — the pallial thickening, the dorsal ventricular ridge, and the putamen. In their physiological characteristics they are similar to the corresponding representation in the general cortex. The absence of significant differences between the latent periods of cortical and striatal evoked potentials to flashes and to stimulation of the dorsal thalamus indicates that visual projection fibers (from the lateral geniculate body) terminate at both cortical and striatal levels. Differences in the distribution of latent periods of unit responses in the cortex to visual and thalamic stimulation are due to the presence of a rotundo-telencephalic visual channel, with direct connections with the striatal and polysynaptic connections with the general cortex, as well as the geniculo-telencephalic tract. Considerable differences between the latent periods of the evoked potentials and also between unit responses to electrodermal stimulation in the cortical and striatal structures indicate that somatic projection fibers relay in the striatum on their path to the general cortex. Consequently, the somatosensory system of turtles is less corticalized than the visual system. Comparison of the results described with those obtained by workers studying other vertebrates suggests that the afferent supply of the striatum may be reorganized in the transition from premammals to mammals.

Development of cerebellar somatosensory evoked potentials in the rat.

Abstract: In lobule VIa of the vermis cerebelli of 69 male albino rats aged from 7 to 90 days we studied the somatosensory potential evoked by electrical stimulation of the sciatic nerve. A response consisting of a marked positive wave and a small negative wave was constantly present in the group of 9- to 10-day-old animals. At the end of the second week, an initial negative wave appeared. The response of 18-day-old animals consisted of 5 waves of alternating polarity and started with a small positive wave as in adult rats. During subsequent development only the relative size of the individual components changed, the later negative wave, N2, being the most marked component in adult animals. An attempted explanation of the possible origin of evoked potentials in young animals, based on the available data on the morphological development of the cerebellar cortex, is submitted. The latent periods, measured to the maxima of the individual waves, shorten abruptly between the 10th and 20th day and then undergo little change. Greater fatigability of the responses of young animals can be demonstrated by using rhythmical stimulation and paired stimuli. Somatosensory responses appear sooner than visual evoked potentials in the cerebellum, but they develop later than somatosensory evoked potentials in the cerebral cortex.

[Changes in the phasic evoked activity of cortical neurons following iontophoretic application of glutamate, GABA and atropine].

Abstract: L-glutamic acid, GABA and atropine were applied ionophoretically from a microelectrode to single neurons in the somatosensory cortex of awake rabbits. The influence of the substances varied for the separate neuron response phases and depended on changes in electric stimulation parameters. A conclusion is made on the chemical specificity of separate phases of the neuronal responses and the neurochemical nature of the changes in the receptive fields of central neurons.

Polysensory interaction in the posterior ventrolateral thalamic nucleus in cats

Abstract: A study of unit activity in the posterior ventrolateral thalamic nucleus in acute experiments on unanesthetized cats revealed neurons (about 20% of those studied) which respond to visual and somatosensory stimulation. By the character of their response to these stimuli, polymodal neurons can be divided into three groups. During the formation of an active defensive reflex to visual and electrodermal stimulation, a rhythm-binding response to flashes was recorded in this nucleus; this response was depressed if a biologically meaningful stimulus was presented at the same time. After division of the optic tract and severance of interhemispheric connections down to the cerebellar level the rhythm-binding response and its depression were found in the posterior ventrolateral thalamic nucleus on the side of the divided optic tract. This fact indicates that the dominant channel for transmission of visual afferentation to this nucleus passes through the brain-stem reticular formation.