Somatosensory system

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

Visual, auditory, and somatosensory convergence on cells in superior colliculus results in multisensory integration

Abstract: Convergence of inputs from different sensory modalities onto individual neurons is a phenomenon that occurs widely throughout the brain at many phyletic levels and appears to represent a basic neural mechanism by which an organism integrates complex environmental stimuli. In the present study, neurons in the superior colliculus (SC) were used as a model to examine how single neurons deal with simultaneous cues from different sensory modalities (e.g., visual, auditory, somatosensory). The functional result of multisensory convergence on an individual cell was determined by comparing the responses evoked from it by a combined-modality (multimodal) stimulus with those elicited by each (unimodal) component of that stimulus presented alone. Superior colliculus cells exhibited profound changes in their activity when individual sensory stimuli were combined. These "multisensory interactions" were found to be widespread among deep laminae cells and fell into one of two functional categories: response enhancement, characterized by a significant increase in the number of discharges evoked; and response depression, characterized by a significant decrease in the discharges elicited. Multisensory response interactions most often reflected a multiplicative, rather than summative, change in activity. Their absolute magnitude varied from cell to cell and, when stimulus conditions were altered, within the same cell. However, the percentage change of enhanced interactions was generally inversely related to the vigor of the responses that could be evoked by presenting each unimodal stimulus alone and suggest that the potential for response amplification was greatest when responses evoked by individual stimuli were weakest. The majority of cells exhibiting multi-sensory characteristics were demonstrated to have descending efferent projections and thus had access to premotor and motor areas of the brain stem and spinal cord involved in SC-mediated attentive and orientation behaviors. These data show that multisensory convergence provides the descending efferent cells of the SC with a dynamic response character. The responses of these cells and the SC-mediated behaviors that they underlie need not be immutably tied to the presence of any single stimulus, but can vary in response to the particular complex of stimuli present in the environment at any given moment.

Nonrepinephrine-containing locus coeruleus neurons in behaving rats exhibit pronounced responses to non-noxious environmental stimuli

Abstract: The effect of sensory stimulation on discharge in norepinephrine- containing locus coeruleus (NE-LC) neurons was studied in unanesthetized behaving rats. Single unit and multiple unit extracellular recordings demonstrated consistent patterns of response. (1) Short latency (15-to 50-msec), transient, biphasic changes in discharge were elicited predictably by non-noxious auditory, visual, and somatosensory stimuli; individual recordings typically exhibited polysensory responsiveness. (2) Sensory-evoked field potentials (FPs) were synchronized with unit responses simultaneously recorded from the same electrodes. (3) The magnitudes of sensory-evoked response varied as a function of vigilance, so that the largest responses occurred for stimuli which awakened animals and the least responsiveness was exhibited during uninterrupted sleep. (4) Sensory responsiveness decreased during grooming and sweet water consumption, similar to the results for sleep. (5) Characteristic response properties were topographically homogeneous throughout the NE-LC. (6) Discharge was synchronized markedly among neurons in multiple unit populations during phasic robust responses. These results are interpreted in light of the preceding report (Aston-Jones, G., and F.E. Bloom (1981) J. Neurosci. 1: 876–886) and studies of the postsynaptic effects of NE to indicate that the NE-LC system may function more in phasic processes than in modulation of the tonic arousal level. We propose that pronouced NE-LC discharge may enhance activity within target cell systems primarily concerned with processing salient external stimuli and suppress cental nervous system activity related more to tonic, vegetative functions. Thus, the NE-LC system may bias global behavioral orientation between stimuli in the external versus internal environments.

Multiple representations of pain in human cerebral cortex

Abstract: The representation of pain in the cerebral cortex is less well understood than that of any other sensory system. However, with the use of magnetic resonance imaging and positron emission tomography in humans, it has now been demonstrated that painful heat causes significant activation of the contralateral anterior cingulate, secondary somatosensory, and primary somatosensory cortices. This contrasts with the predominant activation of primary somatosensory cortex caused by vibrotactile stimuli in similar experiments. Furthermore, the unilateral cingulate activation indicates that this forebrain area, thought to regulate emotions, contains an unexpectedly specific representation of pain.

Thermosensory activation of insular cortex.

Abstract: Temperature sensation is regarded as a submodality of touch, but evidence suggests involvement of insular cortex rather than parietal somatosensory cortices. Using positron emission tomography (PET), we found contralateral activity correlated with graded cooling stimuli only in the dorsal margin of the middle/posterior insula in humans. This corresponds to the thermoreceptive- and nociceptive-specific lamina I spinothalamocortical pathway in monkeys, and can be considered an enteroceptive area within limbic sensory cortex. Because lesions at this site can produce the post-stroke central pain syndrome, this finding supports the proposal that central pain results from loss of the normal inhibition of pain by cold. Notably, perceived thermal intensity was well correlated with activation in the right (ipsilateral) anterior insular and orbitofrontal cortices.