Somatosensory system

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

Posterior Corpus Callosum and Interhemispheric Transfer of Somatosensory Information: An fMRI and Neuropsychological Study of a Partially Callosotomized Patient

Abstract: Interhemispheric somatosensory transfer was studied by functional magnetic resonance imaging (fMRI) and neuropsychological tests in a patient who underwent resection of the corpus callosum (CC) for drug-resistant epilepsy in two stages. The first resection involved the anterior half of the body of CC and the second, its posterior half and the splenium. For the fMRI study, the hand was stimulated with a rough sponge. The neuropsychological tests included: Tactile Naming Test (TNT), Same-Different Recognition Test (SDRT), and Tactile Finger Localization Test (intra- and intermanual tasks, TFLT). The patient was studied 1 week before and then 6 months and 1 year after the second surgery. Before this operation, unilateral tactile stimulation of either hand activated contralaterally the first (SI) and second (SII) somatosensory areas and the posterior parietal (PP) cortex, and SII and PP cortex ipsilaterally. All three tests were performed without errors. In both postoperative sessions, somatosensory activation was observed in contralateral SI, SII, and PP cortex, but not in ipsilateral SII and PP cortex. Performance was 100p correct in the TNT for the right hand, but below chance for the left; in the other tests, it was below chance except for TFLT in the intramanual task. This case provides the direct demonstration that activation of SII and PP cortex to stimulation of the ipsilateral hand and normal interhemispheric transfer of tactile information require the integrity of the posterior body of the CC.

Cortical representation of pain in primary sensory‐motor areas (S1/M1)—a study using intracortical recordings in humans

Abstract: Intracortical evoked potentials to nonnoxious Aβ (electrical) and noxious Aδ (laser) stimuli within the human primary somatosensory (S1) and motor (M1) areas were recorded from 71 electrode sites in 9 epileptic patients. All cortical sites responding to specific noxious inputs also responded to nonnoxious stimuli, while the reverse was not always true. Evoked responses in S1 area 3b were systematic for nonnoxious inputs, but seen in only half of cases after nociceptive stimulation. Nociceptive responses were systematically recorded when electrode tracks reached the crown of the postcentral gyrus, consistent with an origin in somatosensory areas 1-2. Sites in the precentral cortex also exhibited noxious and nonnoxious responses with phase reversals indicating a local origin in area 4 (M1). We conclude that a representation of thermal nociceptive information does exist in human S1, although to a much lesser extent than the nonnociceptive one. Notably, area 3b, which responds massively to nonnoxious Aβ activation was less involved in the processing of noxious heat. S1 and M1 responses to noxious heat occurred at latencies comparable to those observed in the supra-sylvian opercular region of the same patients, suggesting a parallel, rather than hierarchical, processing of noxious inputs in S1, M1 and opercular cortex. This study provides the first direct evidence for a spinothalamic related input to the motor cortex in humans.

POm Thalamocortical Input Drives Layer-Specific Microcircuits in Somatosensory Cortex.

Abstract: Higher-order thalamic nuclei, such as the posterior medial nucleus (POm) in the somatosensory system or the pulvinar in the visual system, densely innervate the cortex and can influence perception and plasticity. To systematically evaluate how higher-order thalamic nuclei can drive cortical circuits, we investigated cell-type selective responses to POm stimulation in mouse primary somatosensory (barrel) cortex, using genetically targeted whole-cell recordings in acute brain slices. We find that ChR2-evoked thalamic input selectively targets specific cell types in the neocortex, revealing layer-specific modules for the summation and processing of POm input. Evoked activity in pyramidal neurons from deep layers is fast and synchronized by rapid feedforward inhibition from GABAergic parvalbumin-expressing neurons, and activity in superficial layers is weaker and prolonged, facilitated by slow inhibition from GABAergic neurons expressing the 5HT3a receptor. Somatostatin-expressing GABAergic neurons do not receive direct input in either layer and their spontaneous activity is suppressed during POm stimulation. This novel pattern of weak, delayed, thalamus-evoked inhibition in layer 2 suggests a longer integration window for incoming sensory information and may facilitate stimulus detection and plasticity in superficial pyramidal neurons.

Effects of stimulus rate on regional cerebral blood flow after median nerve stimulation

Abstract: The primary motor cortex and supplementary motor area (SMA) are purportedly involved in the generation of the P22 and N30 components of somatosensory evoked potentials (SEPs) evoked by electrical stimulation of the median nerve at the wrist. We used regional cerebral blood flow (rCBF) measurements and PET in 10 normal subjects to study the cerebral areas activated by median nerve electrical stimulation. PET scans were performed with the subjects at rest and during stimulation of the right median nerve at frequencies of up to 20 Hz. Stimulation evoked a single focus of activation in the primary somatosensory area (SI). An increase of rCBF in this area was linearly correlated with stimulus frequencies of up to 4 Hz and then reached a plateau. The SMA was not significantly activated by stimulation at any of the frequencies tested. In contrast to the SI, the SMA showed no trend toward a correlation between the rCBF changes and the stimulus repetition rate. In order to achieve maximal resolution in the sensorimotor cortex, regions of interest were placed in individual co-registered MRI-PET images on both sides of the central sulcus. There was no significant increase of rCBF in the crown of the precentral gyrus. These results suggest that a contribution of the primary motor cortex and the SMA to the generation of the P22 and N30 components of SEPs is unlikely. Consequently, functional clinical interpretations derived from P22 or N30 abnormalities must be reconsidered.