Task-relevant modulation of contralateral and ipsilateral primary somatosensory cortex and the role of a prefrontal-cortical sensory gating system.
ABSTRACT Electrophysiological studies have shown that task-relevant somatosensory information leads to selective facilitation within the primary somatosensory cortex (SI). The purpose of the present study was (1) to further explore the relationship between the relevancy of stimuli and activation within the contralateral and ipsilateral SI and (2) to provide further insight into the specific sensory gating network responsible for modulating neural activity within SI. Functional MRI of 12 normal subjects was performed with vibrotactile stimuli presented to the pad of the index finger. In experiment 1, the stimulus was presented to either the left or the right hand. Subjects were required to detect transient changes in stimulus frequency. In experiment 2, stimuli were presented to either the right hand alone or both hands simultaneously. Stimuli were applied either (A) passively or (B) when subjects were asked to detect frequency changes that occurred to the right hand only. In experiment 1, task-relevant somatosensory stimulation led not only to enhanced contralateral SI activity, but also to a suppression of activity in the ipsilateral SI. In experiment 2, SI activation was enhanced when stimuli were task-relevant, compared to that observed with passive input. When stimuli were presented simultaneously to both hands, only those that were task-relevant increased SI activation. This was associated with recruitment of a network of cortical regions, including the right prefrontal cortex (Brodmann area 9). We conclude that SI modulation is dependent on task relevancy and that this modulation may be regulated, at least in part, by the prefrontal cortex.
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ABSTRACT: Crossmodal interactions between relevant visual and tactile inputs can enhance attentional modulation at early stages in somatosensory cortices to achieve goal-oriented behaviors. However, the specific contribution of each sensory system during attentional processing remains unclear. We used EEG to investigate the effects of visual priming and attentional relevance in modulating somatosensory cortical responses. Healthy adults performed a sensory integration task that required scaled motor responses dependent on the amplitudes of tactile and visual stimuli. Participants completed an attentional paradigm comprised of 5 conditions that presented sequential or concurrent pairs of discrete stimuli with random amplitude variations: 1) tactile-tactile (TT), 2) visual-visual (VV), 3) visual-tactile simultaneous (SIM), 4) tactile-visual delay (TVd), and 5) visual-tactile delay (VTd), each with a 100 ms temporal delay between stimulus onsets. Attention was directed to crossmodal conditions and graded motor responses representing the summation of the 2 stimulus amplitudes were made. Results of somatosensory ERPs showed that the modality-specific components (P50, P100) were sensitive to i) the temporal dynamics of crossmodal interactions, and ii) the relevance of these sensory signals for behaviour. Notably, the P50 amplitude was greatest in the VTd condition, suggesting that presentation of relevant visual information for upcoming movement modulates somatosensory processing in modality-specific cortical regions, as early as the primary somatosensory cortex (SI).03/2014; 4(2):247-60. DOI:10.1002/brb3.210
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ABSTRACT: Several studies showed that the transmission of afferent inputs from the periphery to the somatosensory cortex is attenuated during the preparation of voluntary movements. Here, we tested whether sensory attenuation is also observed during the preparation of a voluntary step. It would appear dysfunctional to suppress somatosensory information which is considered to be of the utmost importance for gait preparation. In this context, we predict that the somatosensory information is facilitated during gait preparation. To test this prediction, we recorded cortical somatosensory potentials (SEPs) evoked by bi-lateral lower limb vibration (i.e., proprioceptive inputs) during the preparation phase of a voluntary right foot stepping movement (i.e., Stepping condition). The subjects were also asked to remain still during and after the vibration as a control condition (i.e., Static condition). The amplitude and timing of the early arrival of afferent inflow to the somatosensory cortices (i.e., P1-N1) were not significantly different between the Static and Stepping conditions. However, a large sustained negativity (i.e. late SEP) developed after the P1-N1 component, which was larger when subjects were preparing a step compared to standing. To determine whether this facilitation of proprioceptive inputs was related to gravitational equilibrium constraints, we performed the same experiment in microgravity. In the absence of equilibrium constraints, both the P1-N1 and late SEPs did not significantly differ between the Static and Stepping conditions. These observations provide neurophysiological evidence that the brain exerts a dynamic control over the transmission of the afferent signal according to their current relevance during movement preparation.Journal of Neurophysiology 04/2013; 110(2). DOI:10.1152/jn.00905.2012 · 3.04 Impact Factor
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ABSTRACT: The inter-play between changes in beta-band (14-30-Hz) cortical rhythms and attention during somatosensation informs us about where and when relevant processes occur in the brain. As such, we investigated the effects of attention on somatosensory evoked and induced responses using vibrotactile stimulation and magnetoencephalographic recording. Subjects received trains of vibration at 23 Hz to the right index finger while watching a movie and ignoring the somatosensory stimuli or paying attention to the stimuli to detect a change in the duration of the stimulus. The amplitude of the evoked 23-Hz steady-state response in the contralateral primary somatosensory cortex (SI) was enhanced by attention and the underlying dipole source was located 2 mm more medially, indicating top-down recruitment of additional neuronal populations for the functionally relevant stimulus. Attentional modulation of the somatosensory evoked response indicates facilitation of early processing of the tactile stimulus. Beta-band activity increased after vibration offset in the contralateral primary motor cortex (MI) [event-related synchronization (ERS)] and this increase was larger for attended than ignored stimuli. Beta-band activity decreased in the ipsilateral SI prior to stimulus offset [event-related desynchronization (ERD)] for attended stimuli only. Whereas attention modulation of the evoked response was confined to the contralateral SI, event-related changes of beta-band activity involved contralateral SI-MI and inter-hemispheric SI-SI connections. Modulation of neural activity in such a large sensorimotor network indicates a role for beta activity in higher-order processing.European Journal of Neuroscience 02/2010; 31(4):761-9. DOI:10.1111/j.1460-9568.2010.07094.x · 3.67 Impact Factor