Showing papers on "Somatosensory system published in 1969"

Origin of Somatosensory Evoked Scalp Responses in Man

Abstract: ECAUSE of similarities between somatosensory evoked potentials recorded from the scalp and those arising directly from the brain (animal or man), early components of the scalp response have been thought to arise from the primary sensory area, late ones to originate more diffusely in associated areas or midline cortex at the vertex. 2,5-1~ However, whether these assumptions are correct, whether there is an ipsilateral as well as a contralateral cortical contribution, or whether the entire scalp response derives only from the contralateral primary sensory area, are questions which remain unanswered and with which this paper will deal. The study centers on a group of patients who had selective cortical ablations for epilepsy. For our purpose they afforded a unique opportunity in that some required excision of the somatosensory hand area, either alone, or in addition to other tissue, thus enabling us to compare the effects of such ablations, on the scalp response, with that of other cerebral excisions. Also, during surgery multiple cortical recordings were made from the entire exposed field to identify all cortical areas that are capable of generating a somatosensory response. Comparison of these cortical responses with scalp potentials that were elicited simultaneously provided additional important information. Methods

Some response characteristics of cells of the magnocellular division of the medial geniculate body of the cat

Abstract: Extracellular recordings were made from single units in the magnocellular division of the medial geniculate body of the cat. The stimuli most frequently used were auditory clicks repeated at varying rates and intensities. Somatosensory stimuli were also used to reveal the presence of polysensory units. The response characteristics for most of the cells of the magnocellular division differed from those of the principal division under similar experimental conditions. A difference was noted between the responses obtained from animals which were anesthetized with chloralose and those anesthetized with sodium pentobarbital. It is suggested that the magnocellular division of the medial geniculate body may be divided into two regions, an anterior region which is primarily somatosensory in function and a posterior region which is primarily auditory in function.

Effect of Lesion of the Lateral Geniculate Body on the EEGs and Photically Evoked Potentials in the Cerebral Visual, Somatosensory and Association Areas of Unanesthetized Cat

Abstract: Visually evoked potentials and background EEGs in the cerebral visual, somatosensory, and association areas (lateral suprasylvian gyrus), as well as in the lateral geniculate body (GL) and mesencephalic reticular formation were studied before and after unilateral destruction of the GL of unanes-thetized cat. Autocorrelograms and power spectra of background EEGs in various areas mainly showed activities of less than 5 c/s. Unilateral GL destruction caused considerable depression of the ipsilateral EEG activities and mild depression in the contralateral EEGs in most regions except the somatosensory area, where some augmentation was observed. Unilateral putamen destruction resulted in augmented EEG activities in various areas. GL activity seemed to augment EEG activities in the cerebral visual and association areas, while it seemed to depress the activity in the somato-sensory area. Summation average of evoked potentials in the association area likewise manifested quite similar diphasic deflections within 130 msec after flashing light stimulus. The initial positive deflection P1 led bipolarily in the medial visual association area was found to be longer in duration than in the medial visual area. Peak latencies of the second positive-negative deflection (P2N2) and third positive deflection P3 in the association area were about 10 msec longer than those in the visual area and this was proven to be statistically significant. Amplitudes of the initial and second diphasic deflections in the medial visual area were higher than those in the posterior visual and medial association areas, whereas amplitudes of the third and fourth deflections in the medial visual area were lower than those in the association area. Almost complete destruction of the GL resulted in disappearance of the initial and succeeding diphasic deflections, and there remained a slow negative wave with a crest at about 70 msec after the flashing stimulus which presumably had been masked by the above deflections prior to GL * • Î –ì • @ " O destruction. After partial destruction of the GL, the initial and succeeding deflections were sustained, but prolonged in their peak latencies and decreased in their amplitudes. It was suggested, therefore, that the association area (medial lateral suprasylvian gyrus) may have intimate interaction with the lateral geniculate body, and that the slow negative wave following the initial positive deflection may have been brought out through the indirect nonspecific projection system.