Somatosensory system

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

Functional role of GABA in cat primary somatosensory cortex: shaping receptive fields of cortical neurons.

Abstract: Extracellular recordings of 209 neurons were obtained with carbon fiber-containing multibarrel micropipettes. The cells were isolated in the primary somatosensory cortex of cats anesthetized with barbiturate and classified according to the nature of their response to natural stimuli, the nature of the surrounding multiunit responses to the same stimuli, the response to thalamic stimulation, and their depth in the cortex. To study factors controlling the excitability of somatosensory neurons, their receptive fields were examined in the presence of iontophoretically administered gamma-aminobutyric acid (GABA), glutamate, and bicuculline methiodide (BMI). Even when the neurons were depolarized to perithreshold levels with glutamate, or when local inhibitory influences mediated by GABA were antagonized by BMI, the apparent specificity for one class of afferent input was maintained. Neurons responding to stimulation of either cutaneous or deep receptors maintained their modality specificity, and neurons in cutaneous rapidly adapting regions never took on slowly adapting properties. When ejected at currents that did not elicit action potentials, glutamate lowered the threshold for activation by cutaneous stimuli but did not enlarge the receptive field. With larger ejecting currents, the neurons developed an on-going discharge, but even at these higher doses, glutamate did not produce an increase in the receptive-field size. Some neurons in regions of cortex exhibiting slowly adapting multiunit responses were relatively insensitive to glutamate. These cells required four to five times more glutamate to evoke discharges than did most neurons. Other cells, previously unresponsive to somatic stimuli, could be shown to possess distinct cutaneous receptive fields when either glutamate or BMI was ejected in their vicinity. Iontophoretically administered BMI altered the firing pattern of somatosensory neurons, causing them to discharge in bursts of 3-15 impulses. BMI enlarged the receptive-field size of neurons in regions displaying rapidly adapting multiunit background discharges but not in those regions with slowly adapting multiunit discharges. This differential effect of BMI, suggesting that GABA controls receptive-field size in rapidly adapting regions, also indicates that neurons in rapidly adapting regions differ pharmacologically from those in other submodality regions. In all cortical regions, BMI blocked the poststimulus inhibitory period that normally followed thalamic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Extensive reorganization of the somatosensory cortex in adult humans after nervous system injury

Abstract: MAGNETIC source imaging revealed that the topographic representation in the somatosensory cortex of the face area in upper extremity amputees was shifted an average of 1.5 cm toward the area that would normally receive input from the now absent nerves supplying the hand and fingers. Observed alterat

Gamma Oscillations in Human Primary Somatosensory Cortex Reflect Pain Perception

Abstract: Successful behavior requires selection and preferred processing of relevant sensory information. The cortical representation of relevant sensory information has been related to neuronal oscillations in the gamma frequency band. Pain is of invariably high behavioral relevance and, thus, nociceptive stimuli receive preferred processing. Here, by using magnetoencephalography, we show that selective nociceptive stimuli induce gamma oscillations between 60 and 95 Hz in primary somatosensory cortex. Amplitudes of pain-induced gamma oscillations vary with objective stimulus intensity and subjective pain intensity. However, around pain threshold, perceived stimuli yielded stronger gamma oscillations than unperceived stimuli of equal stimulus intensity. These results show that pain induces gamma oscillations in primary somatosensory cortex that are particularly related to the subjective perception of pain. Our findings support the hypothesis that gamma oscillations are related to the internal representation of behaviorally relevant stimuli that should receive preferred processing.

Transformation from temporal to rate coding in a somatosensory thalamocortical pathway

Abstract: The anatomical connections from the whiskers to the rodent somatosensory (barrel) cortex form two parallel (lemniscal and paralemniscal) pathways. It is unclear whether the paralemniscal pathway is directly involved in tactile processing, because paralemniscal neuronal responses show poor spatial resolution, labile latencies and strong dependence on cortical feedback. Here we show that the paralemniscal system can transform temporally encoded vibrissal information into a rate code. We recorded the representations of the frequency of whisker movement along the two pathways in anaesthetized rats. In response to varying stimulus frequencies, the lemniscal neurons exhibited amplitude modulations and constant latencies. In contrast, paralemniscal neurons in both thalamus and cortex coded the input frequency as changes in latency. Because the onset latencies increased and the offset latencies remained constant, the latency increments were translated into a rate code: increasing onset latencies led to lower spike counts. A thalamocortical loop that includes cortical oscillations and thalamic gating can account for these results. Thus, variable latencies and effective cortical feedback in the paralemniscal system can serve the processing of temporal sensory cues, such as those that encode object location during whisking. In contrast, fixed time locking in the lemniscal system is crucial for reliable spatial processing.

Residual function in peripheral nerve stumps of amputees: implications for neural control of artificial limbs.

Abstract: Purpose It is not known whether motor and sensory pathways associated with a missing or denervated limb remain functionally intact over periods of many months or years after amputation or chronic peripheral nerve transection injury. We examined the extent to which activity on chronically severed motor nerve fibers could be controlled by human amputees and whether distally referred tactile and proprioceptive sensations could be induced by stimulation of sensory axons in the nerve stumps. Methods Amputees undergoing elective stump procedures were invited to participate in this study. Longitudinal intrafascicular electrodes were threaded percutaneously and implanted in severed nerves of human amputees. The electrodes were interfaced to an amplifier and stimulator system controlled by a laptop computer. Electrophysiologic tests were conducted for 2 consecutive days after recovery from the surgery. Results It was possible to record volitional motor nerve activity uniquely associated with missing limb movements. Electrical stimulation through the implanted electrodes elicited discrete, unitary, graded sensations of touch, joint movement, and position, referring to the missing limb. Conclusions These findings indicate that both central and peripheral motor and somatosensory pathways retain significant residual connectivity and function for many years after limb amputation. This implies that peripheral nerve interfaces could be used to provide amputees with prosthetic limbs that have more natural feel and control than is possible with current myoelectric and body-powered control systems.