Functional Organization Of Somatosensory Cortex Research Articles

Dynamic shifts in the organization of primary somatosensory cortex induced by bimanual spatial coupling of motor activity

Previous work has shown that training and learning can induce powerful changes in the homuncular organization of the primary somatosensory cortex (SI). Moreover, a number of studies suggest the existence of short-term adaptation of representational maps in SI. Recently, motor activity has been shown to induce rapid modulation of somatosensory cortical maps. It is hypothesized that there is a task-related influence of motor and premotor areas upon the organization of somatosensory cortex. In order to test this hypothesis, we studied the functional organization of somatosensory cortex by examining coupling effects in a bimanual movement task. Bimanual coupling is known to be related to an activation of the premotor cortex and the supplementary motor area. The functional organization of the somatosensory cortex for known bimanual coupling effects was compared to the organization of the somatosensory cortex during the same movements but with only a small effort in coupling. Topography of the functional organization of the somatosensory cortex was assessed using neuromagnetic source imaging based on tactile stimulation of the first (D1) and fifth digit (D5). We could show that the cortical representations of D1 and D5 moved further apart during the bimanual coupling task in comparison to the same task without coupling and rest. Our data suggest that somatosensory cortical maps undergo fast and dynamic modulation as a result of a task-related influence of motor or premotor areas.

Task-specific plasticity of somatosensory cortex in patients with writer's cramp

Focal dystonias such as writer's cramp are characterized by muscular cramps that accompany the execution of specific motor tasks. Until now, the pathophysiology of focal dystonia remains incompletely understood. Recent studies suggest that the development of writer's cramp is related to abnormal organization of primary somatosensory cortex (SI), which in turn leads to impaired motor function. To explore contributions of SI on mechanisms of task specificity in focal dystonia, we investigated dynamic alterations in the functional organization of SI as well as sensory-motor gating for rest, left- and right-handed writing and brushing in writer's cramp patients and healthy controls. The functional organization of somatosensory cortex was assessed by neuromagnetic source imaging (151 channel whole-head MEG). In accordance with previous reports, distances between cortical representations of thumb and little finger of the affected hand were smaller in patients compared to healthy subjects. However, similar to healthy controls, patients showed normal modulation of the functional organization of SI as induced by the execution of different motor tasks. Both in the control subjects and patients, cortical distances between representations of thumb and little finger increased when writing and brushing compared to the resting condition. Although, cramps only occured during writing, no differences in the organization of SI were seen among motor tasks. Our data suggest that despite alterations in the organization of primary somatosensory cortex in writer's cramp, the capability of SI to adapt dynamically to different tasks is not impaired.

MEG Reveals the Functional Organization of Somatosensory Cortex Using Automated Analyses

MEG Reveals the Functional Organization of Somatosensory Cortex Using Automated Analyses

The functional organization of somatosensory cortex in primates

Our understanding of the functional organization of somatosensory cortex and thalamus in primates and other mammals has greatly increased over the last few years. It is now clear that higher primates have four strip-like representations of skin and muscle receptors corresponding to areas 3 a, 3b, 1 and 2 of anterior parietal cortex. Areas 3b and 1 receive cutaneous information from the ventroposterior nucleus, while a ventroposterior superior nucleus provides areas 3a and 2 with information from muscle receptors. Area 3b is the homolog of S-I in prosimians and non-primates and it provides most of the activating cutaneous inputs to areas 1 and 2. Most of the further processing that allows tactile recognition of objects involves somatosensory areas of the lateral sulcus, where both S-II and the parietal ventral area (PV) receive activating inputs from areas 3a, 3b, 1 and 2. S-II also projects to PV and to a parietal rostral area where further connections with the amygdala and hippocampus may occur to allow the formation of tactile memories. Areas of anterior parietal cortex also project to posterior parietal cortex, where regions of cortex are largely somatosensory, but the functional subdivisions remain uncertain. All of the somatosensory fields have access to motor areas of the frontal lobe, but the magnitude and targets of the projections differ.

The organization and connections of somatosensory cortex in primates

The use of microelectrode mapping methods, in conjunction with studies of cortical architecture, patterns of connections, and the response properties of single neurons, has led to a greatly increased understanding of the functional organization of somatosensory cortex in mammals. All mammals appear to have the traditionally defined first and second somatosensory representations, SI and SII, but at least some mammals have additional body representations as well. Furthermore, the area traditionally regarded as “SI” in monkeys actually includes four functionally distinct representations. Within “SI,” four striplike architectonic fields, areas 3a, 3b, 1, and 2 have long been recognized. It is now clear that areas 3b and 1 form separate parallel and largely mirror‐image representations of the body surface, each with major inputs from a single representation of the body surface in the ventroposterior nucleus (VP) of the thalamus. VP appears to relay information from both slowly and rapidly adapting peripheral neurons to area 3b, while information from rapidly adapting neurons is relayed to area 1. Neurons with properties that could reflect Pacinian receptor influences are found in area 1, but not area 3b. The anatomical pathways mediating Pacinian‐like responses are unknown. Area 3a contains a representation of largely deep receptors, probably muscle spindle afferents, relayed from part of the thalamus dorsal to VP. Area 2 forms a representation of both deep and cutaneous body receptors. The somatosensory cortex receives input from other regions as well, including the anterior pulvinar and ventroposterior inferior nucleus of the thalamus. Other portions of the somatosensory cortex are less well understood.

Functional reorganization of adult raccoon somatosensory cerebral cortex following neonatal digit amputation

Amputation of a forepaw digit in raccoons 2–8 weeks of age produced dramatic changes in the functional organization of somatosensory cortex examined electrophysiologically 9–12 months later. The cortical region normally representing the digit that was amputated received widely overlapping input from the entire forepaw, with local disruption of somatotopic organization. Compared with normal animals, the receptive fields of cortical neurons in amputated animals were larger, often included both glabrous and hairy skin, sometimes involved discontinuous skin regions, and were much more variable in peripheral location as a function of recording distance across the cortex and of depth within the cortex.