Somatosensory system

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

Somatotopic maps are disorganized in adult rodents treated neonatally with capsaicin.

Abstract: The somatosensory system is characterized at each stage of the projection pathways by the presence of maps formed by an orderly arrangement of cells and of the incoming fibres. Each cell responds to a definite area of skin, its receptive field (RF). If cell locations and their RFs are plotted side by side, they make up a continuous map of the body surface. Given the stability and repeatability of these maps, it was of interest to find that lesions which destroyed the input to one part of the map of the spinal cord in adults were followed by a readjustment of the RFs of cells which had lost their normal input1. It was more surprising to discover in adult cats and rats that peripheral nerve lesions which do not produce an anatomical destruction of spinal cord afferents were followed by the appearance of novel RFs in cells deprived of their normal physiological input2,3. Capsaicin given to neonatal mice or rats destroys unmyelinated afferents. We report here that this is followed by an expansion of the normal receptive fields supplied by myelinated afferents2,3. Our results suggest that unmyelinated fibres may be involved in controlling the connectivity of myelinated afferents with first central cells.

Large-scale reorganization of the somatosensory cortex following spinal cord injuries is due to brainstem plasticity

Abstract: Adult mammalian brains undergo reorganization following deafferentations due to peripheral nerve, cortical or spinal cord injuries. The largest extent of cortical reorganization is seen in area 3b of the somatosensory cortex of monkeys with chronic transection of the dorsal roots or dorsal columns of the spinal cord. These injuries cause expansion of intact face inputs into the deafferented hand cortex, resulting in a change of representational boundaries by more than 7 mm. Here we show that large-scale reorganization in area 3b following spinal cord injuries is due to changes at the level of the brainstem nuclei and not due to cortical mechanisms. Selective inactivation of the reorganized cuneate nucleus of the brainstem eliminates observed face expansion in area 3b. Thus, the substrate for the observed expanded face representation in area 3b lies in the cuneate nucleus.

KCNQ4 K(+) channels tune mechanoreceptors for normal touch sensation in mouse and man.

Abstract: Mutations inactivating the potassium channel KCNQ4 (K(v)7.4) lead to deafness in humans and mice. In addition to its expression in mechanosensitive hair cells of the inner ear, KCNQ4 is found in the auditory pathway and in trigeminal nuclei that convey somatosensory information. We have now detected KCNQ4 in the peripheral nerve endings of cutaneous rapidly adapting hair follicle and Meissner corpuscle mechanoreceptors from mice and humans. Electrophysiological recordings from single afferents from Kcnq4(-/-) mice and mice carrying a KCNQ4 mutation found in DFNA2-type monogenic dominant human hearing loss showed elevated mechanosensitivity and altered frequency response of rapidly adapting, but not of slowly adapting nor of D-hair, mechanoreceptor neurons. Human subjects from independent DFNA2 pedigrees outperformed age-matched control subjects when tested for vibrotactile acuity at low frequencies. This work describes a gene mutation that modulates touch sensitivity in mice and humans and establishes KCNQ4 as a specific molecular marker for rapidly adapting Meissner and a subset of hair follicle afferents.

Functional roles of rhythmic neuronal activity in the human visual and somatosensory system

Abstract: The main aim of this thesis was to investigate the functional role of synchronised oscillations in sensory systems of the human brain. In the first study we found high-frequency gamma-oscillations in the somatosensory system in response to mechanical tactile stimulation. These stimulus-related high-frequency oscillations have been described before in other sensory systems, but not in the somatosensory system in response to tactile stimulation. Its functional relevance was assessed by means of a spatial selective attention task. We found that performance of this task caused a variety of changes in neural activity with different temporal dynamics: The main affect of attention on stimulus-related activity was an enhancement of somatosensory gamma-band-activity, while low-frequency activity in the alpha- and beta-band were altered largely independently from stimulation. Tactile stimulation also altered neural activity in occipital cortex. We therefore investigated how simultaneous visual and tactile stimulation influence activity in visual cortex compared to unimodal stimulation, and as a function of the spatial relation between the two stimuli. We found that in occipital cortex, primarily gamma-band activity was enhanced by tactile stimulation (irrespective of location) and that this effect corresponded with the shortening of response latencies to visual stimuli by tactile stimulation. We further investigated the role of oscillatory activity in sensory information transmission using a visual detection task, where stimuli were presented at threshold level. The main result from this study was that (presumably non-stimulus-related) beta-band-activity in a parieto-frontal network discriminated best between successful and unsuccesful performance. Together the results show that rhythmic activity in sensory cortex is not only altered by stimulation but also correlates with various cognitive and behavioural parameters, suggesting it has a function role. A differential pattern of high- and low-frequency activity in response to bottom-up and top-down-activation was observed and is of interest for further research.