Somatosensory system

About: Somatosensory system is a research topic. Over the lifetime, 6371 publications have been published within this topic receiving 316900 citations.

Depression of cortical somatosensory evoked potentials by nitrous oxide

Abstract: The effects of the inhalation of50% nitrous oxide on somatosensory evoked potentials during a fentanyf-oxygen anaesthetic technique for central nervous system surgery were evaluated. The latency and amplitude of the first cortical wave were obtained using conventional somatosensory techniques with median or posterior tibialnerve stimulation. Data were collected before and after the inhalation of 50% nitrous oxide in oxygen introduced at the conclusion of the surgical procedure. The addition of nitrous oxide was associated with consistent decreases in the amplitude of somatosensory evoked potentials, but with no significant changes in latency. Since no electrical, physiological, or surgical event was associated with these changes, the results suggest that they were attributable to nitrous oxide per se.

Rapid functional plasticity in the primary somatomotor cortex and perceptual changes after nerve block

Abstract: The mature human primary somatosensory cortex displays a striking plastic capacity to reorganize itself in response to changes in sensory input. Following the elimination of afferent return, produced by either amputation, deafferentation by dorsal rhizotomy, or nerve block, there is a well-known but little-understood ‘invasion’ of the deafferented region of the brain by the cortical representation zones of still-intact portions of the brain adjacent to it. We report here that within an hour of abolishing sensation from the radial and medial three-quarters of the hand by pharmacological blockade of the radial and median nerves, magnetic source imaging showed that the cortical representation of the little finger and the skin beneath the lower lip, whose intact cortical representation zones are adjacent to the deafferented region, had moved closer together, presumably because of their expansion across the deafferented area. A paired-pulse transcranial magnetic stimulation procedure revealed a motor cortex disinhibition for two muscles supplied by the unaffected ulnar nerve. In addition, two notable perceptual changes were observed: increased two-point discrimination ability near the lip and mislocalization of touch of the intact ulnar portion of the fourth finger to the neighbouring third finger whose nerve supply was blocked. We suggest that disinhibition within the somatosensory system as a functional correlate for the known enlargement of cortical representation zones might account for not only the ‘invasion’ phenomenon, but also for the observed behavioural correlates of the nerve block.

Sensory properties and afferents of the N. dorsolateralis posterior thalami of the pigeon

Abstract: According to previous studies, the avian n. dorsolateralis posterior thalami (DLP) receives visual and somatosensory afferents. While some authors (e.g., Gamlin and Cohen: J. Comp. Neurol. 250:296-310, '86) proposed a distinction between a visual caudal (DLPc) and a somatosensory rostral (DLPr) part, other authors (e.g., Wild: Brain Res. 412:205-223, '87) could not confirm such a differentiation. The aim of the present experiment was to study with physiological and anatomical methods the proposed parcellation of the DLP into various components dealing with different modalities. The physiological properties of the DLP of the pigeon were analysed with extracellular single unit recordings. With the same approach, neurons of the n. dorsalis intermedius ventralis anterior (DIVA), a somatosensory relay nucleus in the dorsal thalamus, were also analysed. The afferents of the DLP were studied by using anatomical tract tracing techniques with retrograde and anterograde tracers. The sensory properties of DLP cells revealed that somatosensory, visual, and auditory modalities affect the neuronal firing frequency in this nucleus. All three modalities were present throughout the full caudorostral extent of the DLP. Cells recorded in DIVA responded nearly exclusively to somatosensory stimulation. Unlike the DLP, single units in DIVA generally had smaller receptive fields encompassing only one extremity. The analysis of afferent connections of the DLP by using injections of retrograde and anterograde tracers (HRP, WGA-HRP, Fast Blue, and Rhodamine-beta-isothiocyanate) demonstrated extensive projections from the nuclei gracilis et cuneatus (GC) and more sparse projections from the nucleus tractus descendens trigemini (TTD), and the nucleus cuneatus externus (CE). Brainstem afferents of the DLP came from different vestibular nuclei, various areas of the brainstem reticular formation, and the optic tectum. Prosencephalic afferents originated in the n. posteroventralis thalami (PV), the n. ventromedialis posterior thalami (VMP), the n. dorsalis intermedius ventralis anterior (DIVA), and the nucleus reticularis superior pars dorsalis and ventralis (RSd and RSv). Telencephalic afferents of the DLP came from the hyperstriatum accessorium (HA) and a group of cells at the borderline between the hyperstriatum intercalatus superior (HIS) and the hyperstriatum dorsale (HD). The somatosensory afferents of the DLP probably originate from the GC, TTD, and CE, whereas it is likely that the visual input is mediated by the optic tectum. The anatomical source for the acoustic input is unclear. The very long latencies of auditory DLP neurons make it likely that the acoustic input originates at least partly in the reticular formation.(ABSTRACT TRUNCATED AT 400 WORDS)