Somatosensory system

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

Modality-Specific Perceptual Expectations Selectively Modulate Baseline Activity in Auditory, Somatosensory, and Visual Cortices

Abstract: Valid expectations are known to improve target detection, but the preparatory attentional mechanisms underlying this perceptual facilitation remain an open issue. Using functional magnetic resonance imaging, we show here that expecting auditory, tactile, or visual targets, in the absence of stimulation, selectively increased baseline activity in corresponding sensory cortices and decreased activity in irrelevant ones. Regardless of sensory modality, expectancy activated bilateral premotor and posterior parietal areas, supplementary motor area as well as right anterior insula and right middle frontal gyrus. The bilateral putamen was sensitive to the modality specificity of expectations during the unexpected omission of targets. Thus, across modalities, detection improvement arising from selectively directing attention to a sensory modality appears mediated through transient changes in pretarget activity. This flexible advance modulation of baseline activity in sensory cortices resolves ambiguities among previous studies unable to discriminate modality-specific preparatory activity from attentional modulation of stimulus processing. Our results agree with predictive-coding models, which suggest that these expectancy-related changes reflect top-down biases--presumably originating from the observed supramodal frontoparietal network--that modulate signal-detection sensitivity by differentially modifying background activity (i.e., noise level) in different input channels. The putamen appears to code omission-related Bayesian "surprise" that depends on the specificity of predictions.

Somatosensory cortical atrophy after spinal cord injury: A voxel-based morphometry study

Abstract: The authors used voxel-based morphometry to compare sensorimotor cortical gray and white matter volume on structural MR images of a group of 17 individuals with cervical spinal cord injury (SCI) and a group of 17 healthy subjects. SCI subjects had reduced gray matter volume bilaterally in primary somatosensory cortex (p < 0.001). These findings suggest that the somatosensory cortex of the human brain atrophies after SCI.

Somatosensory System in Two Types of Motor Reorganization in Congenital Hemiparesis : Topography and Function

Abstract: This study investigates the (re-)organization of somatosensory functions following early brain lesions. Using functional magnetic resonance imaging (fMRI), passive hand movement was studied. Transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) were used as complementary methods. fMRI data was analyzed on the first level with regard to topographical variability; second-level group effects as well as the overall integrity of the somatosensory circuitry were also assessed. Subjects with unilateral brain lesions occurring in the third trimester of pregnancy or perinatally with different types of motor reorganization were included: patients with regular, contralateral motor organization following middle cerebral artery strokes (CONTRA(MCA), n = 6) and patients with reorganized, ipsilateral motor functions due to periventricular lesions (IPSI(PL), n = 8). Motor impairment was similar, but sensory impairment was more pronounced in the CONTRA(MCA) group. Using fMRI and MEG, both groups showed a normal pattern with a contralateral somatosensory representation, despite the transhemispherically reorganized primary motor cortex in the IPSI(PL) group, as verified by TMS. Activation topography for the paretic hands was more variable than for the nonparetic hand in both groups. The cortico-cerebellar circuitry was well-preserved in almost all subjects. We conclude that in both models of motor reorganization, no interhemispheric reorganization of somatosensory functions occurred. Also, no relevant intrahemispheric reorganization was observed apart from a higher topographical variability of fMRI activations. This preserved pattern of somatosensory organization argues in favor of a differential lesion effect on motor and somatosensory functions and demonstrates a limited compensatory potential for the latter.

Vibrissal motor cortex in the rat: connections with the barrel field.

Abstract: The flow of information in the sensorimotor cortex may determine how somatic information modulates motor cortex neuronal activity during voluntary movement. Electrophysiological recordings and neuroanatomical tracing techniques were used to study the connections between the primary somatosensory cortex (SI) and the vibrissal representation of the primary motor cortex (MI) in rodents. Intracortical microstimulation (ICMS) was applied to the vibrissal region of the motor cortex to identify a site from which stimulation evoked movements of the vibrissae. Movements of only a single whisker were evoked by applying low-intensity stimulating current to particular locations within MI. A single injection of either horseradish peroxidase (HRP) or biocytin was made at the stimulus site in each animal, to retrogradely label cells in the somatosensory cortex. Receptive field (RF) responses were recorded from neurons in the barrel cortex to identify the sensory cortex representation of the same whisker that responded to ICMS. The site at which neurons responded predominately to manual stimulation of this particular vibrissa was marked by a small electrolytic lesion. The projection from the somatosensory cortex to the identified whisker representation in the motor cortex was determined by mapping the location of labeled neurons in tissue sections processed for either HRP or biocytin. The relationship of the labeled cells in SI to the barrel structures was determined from adjacent sections that were stained for cytochrome oxidase. In all cases, the barrel column associated with the relevant whisker contained labeled cells. Surrounding barrels also contained labeled cells, although fewer in number. Very few labeled cells were found in non-contiguous barrels. These results show that the SI to MI projection is somatotopically arranged, such that the sensory cortex representation of a whisker is morphologically connected to the motor cortex representation of the same whisker. Thus, sensory information is relayed to MI from the relevant whisker region in SI. Adjacent whisker regions also appear to relay somatic input, but presumably to a lesser degree. A second group of animals received single small injections of the anterograde tracer, Phaseolus vulgaris leucoagglutinin, to an electrophysiologically identified whisker representation in the sensory cortex. A single narrow column of labeled fibers was found in the motor cortex following such injections. Thus, the sensory cortex appears to relay somatic information from the vibrissae to restricted regions of the motor cortex in a somatotopically organized manner. Furthermore, the stimulus-evoked whisker movements suggest that certain features of the output map of the motor cortex are discretely organized. These input/output relationships suggest that complex information processing within the vibrissal sensorimotor cortex is highly organized.