Somatosensory system

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

Is the Medial Posterior Parietal Area V6A a Single Functional Area

Abstract: The visuomotor medial posterior parietal area V6A has been recently subdivided into two cytoarchitectonic sectors called V6Ad and V6Av (Luppino et al., 2005). The aim of the present study was to recognize whether these two cortical sectors show different functional profiles. Fourteen hemispheres from eight animals (Macaca fascicularis) were included in this study, for a total of 3828 extracellularly recorded neurons assigned to areas V6Ad or V6Av on cytoarchitectural basis. The sensitivity of recorded neurons to sensory- and motor-related activities was checked with a series of functional tests performed on behaving animals. We found that cells sensitive to visual stimuli were more represented in V6Av and cells sensitive to somatosensory stimuli were more represented in V6Ad. Visual cells directly encoding spatial locations (real-position cells) were present only in V6Av. Cells encoding basic visual and somatic properties as well as different aspects of reaching and grasping activities were present in both sectors of V6A, although with different incidence. Cells that had reach-related activity enhanced by visual feedback and grasping neurons activated by whole-hand prehension were more concentrated in V6Av. Conversely, reaching neurons inhibited by visual feedback and grasping neurons activated by precision grip were more represented in V6Ad. Although V6Av and V6Ad show partly different functional profiles, our data support the idea that V6A is a single functional area involved in the control of reach-to-grasp movements, with the dorsal sector (V6Ad) more involved in the somatomotor control and the ventral sector (V6Av) in the visual control of reaching and grasping actions.

Dynamic organization of the somatosensory cortex induced by motor activity

Abstract: Intensive and long-lasting experience of altered sensory input induces permanent changes in the functional organization of the somatosensory cortex. In addition, an increasing body of evidence suggests the existence of dynamic, short-term and task-dependent adaptation of representational maps within somatosensory cortex. It is hypothesized that somatosensory maps can, not only, be acquired within a short period of time, but might also be set up during periods of training related to specific tasks and subsequently activated dynamically upon performance of that particular task. In order to test this hypothesis we studied the functional organization of somatosensory cortex for a heavily overlearned and frequently performed task for which no new acquisition of a sensory map had to be assumed. To this end, the functional organization of somatosensory cortex for handwriting was compared with the organization during rest in healthy humans. Functional organization of the somatosensory cortex was assessed using non-invasive, neuromagnetic source imaging based on tactile stimulation of the thumb (D1) and little finger (D5) during writing and rest. In different blocks, subjects wrote with their right, dominant and their left hand, respectively. During writing, D1 and D5 of the writing hand were stimulated. To test the reliability of our results all measurements were repeated after 1 week. It was found that amplitudes of somatosensory evoked magnetic fields with latencies of 45 ms were reduced during writing compared with rest. This finding is in accordance with the sensorimotor gating effect. Using source localization we could show that cortical representations of D1 and D5 are more distant during writing with either hand compared with rest. Our data suggest that somatosensory cortical maps undergo rapid modulation depending on task-specific involvement of sensory processing in daily-life overlearned movements. As it is unlikely that a new sensory map is always acquired when a frequently used task such as writing is performed, we suggest that somatosensory cortex switches between different, concurrently pre-existing maps depending on actual requirements. Task-dependent activation of pre-existing maps might be a powerful mechanism to optimize stimulus processing.

Spinal and supraspinal correlates of nociception in man.

Abstract: The objective of this work was to simultaneously measure pain-related spinal and supraspinal physiological responses in humans. The sural nerve compound action potential (CAP), the spinal withdrawal reflex (RIII), the somatosensory evoked potential (SEP) and subjective magnitude ratings were elicited by electrical stimulation of the sural nerve in 10 healthy subjects. The sural nerve CAP was used to normalize the evoking stimulus current and to help identify the peripheral nerve afferent types contributing to the physiological and psychophysical responses. Normalizing stimulus current to a proportion of that which elicited a just maximal sural nerve CAP significantly reduced individual variability in magnitude ratings, the RIII and the SEP. Pain and RIII responses only occurred at stimulus levels that were greater than or equal to 1.5 x that which produced a just maximal sural nerve CAP and both responses were positively related to stimulus intensity above that level. Activity in the large diameter A beta fibers will be saturated at stimulus levels near that which produced a just maximal CAP, which implies that both the pain and RIII responses can be attributed to recruitment of the smaller diameter A delta fibers. Although the amplitudes of the P200 and P300 peaks of the SEP were significantly related to stimulation at noxious levels, both were also affected by stimulation at innocuous levels. This result implies that these peaks receive contributions from both noxious and innocuous somatosensory processes. Clearly, the non-pain-related components of these SEP peaks must be identified and isolated before their potential in measuring supraspinal nociceptive processes can be fully realized.

Functional Independence of Layer IV Barrels in Rodent Somatosensory Cortex

Abstract: Layer IV of rodent primary somatosensory cortex is characterized by an array of whisker-related groups of neurons, known as “barrels.” Neurons within each barrel respond best to a particular whiske...

Stimulation of motor tracts in motor neuron disease.

Abstract: The muscle responses evoked by cortical and cervical stimulation in 11 patients with motor neuron disease were studied. The muscle potential in the abductor pollicis brevis, evoked by median nerve stimulation and the somatosensory potential evoked by wrist stimulation were also studied. In eight of 11 patients there was absence or increased central delay of the responses evoked by cortical stimulation. In four patients muscle responses on cervical stimulation and muscle action potentials on median nerve stimulation were also altered, indicating peripheral abnormalities. Somatosensory responses evoked by wrist stimulation were normal. Electrophysiological techniques are helpful in estimating the site of motor involvement in motor neuron disease.