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.
"There is accumulating evidence that the brain dynamically increases the weight of somatosensory inputs during the preparation and execution of movements whose control largely depends on proprioceptive or cutaneous feedback (Blouin et al., 2014; Cybulska-Klosowicz et al., 2011; Knecht et al., 1993; Staines et al., 2002; Saradjian et al., 2013). "
"Movement, in particular those whose control relies on sensory feedback can improve the transmission of sensory inputs that are known to be gated prior to and during a voluntary movement –. Indeed, cortical responsiveness to sensory stimuli can be increased during the execution of voluntary movements by alleviating the gating of sensory inputs to suit task-specific demands –. In addition, the amount of signal transmitted to the cerebral cortex is not uniform over the execution of a voluntary movement and can be dynamically modulated while the movement is being performed. "
[Show abstract][Hide abstract] ABSTRACT: We recently found that the cortical response to proprioceptive stimulation was greater when participants were planning a step than when they stood still, and that this sensory facilitation was suppressed in microgravity. The aim of the present study was to test whether the absence of gravity-related sensory afferents during movement planning in microgravity prevented the proprioceptive cortical processing to be enhanced. We reestablished a reference frame in microgravity by providing and translating a horizontal support on which the participants were standing and verified whether this procedure restored the proprioceptive facilitation. The slight translation of the base of support (lateral direction), which occurred prior to step initiation, stimulated at least cutaneous and vestibular receptors. The sensitivity to proprioceptive stimulation was assessed by measuring the amplitude of the cortical somatosensory-evoked potential (SEP, over the Cz electrode) following the vibration of the leg muscle. The vibration lasted 1 s and the participants were asked to either initiate a step at the vibration offset or to remain still. We found that the early SEP (90-160 ms) was smaller when the platform was translated than when it remained stationary, revealing the existence of an interference phenomenon (i.e., when proprioceptive stimulation is preceded by the stimulation of different sensory modalities evoked by the platform translation). By contrast, the late SEP (550 ms post proprioceptive stimulation onset) was greater when the translation preceded the vibration compared to a condition without pre-stimulation (i.e., no translation). This suggests that restoring a body reference system which is impaired in microgravity allowed a greater proprioceptive cortical processing. Importantly, however, the late SEP was similarly increased when participants either produced a step or remained still. We propose that the absence of step-induced facilitation of proprioceptive cortical processing results from a decreased weight of proprioception in the absence of balance constraints in microgravity.
PLoS ONE 09/2014; 9(9):e108636. DOI:10.1371/journal.pone.0108636 · 3.23 Impact Factor
"It is well-known that attention can modulate neurophysiological responses in modality-specific cortices including: visual (Motter, 1993; Gazzaley et al., 2007; Andersen et al., 2008), auditory (Woldorff et al., 1993; Jäncke et al., 1999; Petkov et al., 2004), and somatosensory cortices (Josiassen et al., 1990; Hsiao et al., 1993; Johansen-Berg et al., 2000; Staines et al., 2002). However, recent investigations have begun to examine whether attention influences neural responses across sensory modalities when sensory input from more than one modality is present. "
[Show abstract][Hide abstract] ABSTRACT: Bimodal interactions between relevant visual and tactile inputs can facilitate attentional modulation at early stages in somatosensory cortices to achieve goal-oriented behaviors. However, the specific contribution of each sensory system during attentional processing and, importantly, how these interact with the required behavioural motor goals remains unclear. Here we used EEG and event-related potentials (ERPs) to test the hypothesis that activity from modality-specific somatosensory cortical regions would be enhanced with task-relevant bimodal (visual-tactile) stimuli and that the degree of modulation would depend on the difficulty of the associated sensory-motor task demands. Tactile stimuli were discrete vibrations to the index finger and visual stimuli were horizontal bars on a computer screen, both with random amplitudes. Streams of unimodal (tactile) and crossmodal (visual and tactile) stimuli were randomly presented and participants were instructed to attend to one type of stimulus (unimodal or crossmodal) and responses involved either an indication of the presence of an attended stimulus (detect), or the integration and summation of 2 stimulus amplitudes using a pressure-sensitive ball (grade). Force-amplitude associations were learned in a training session, and no feedback was provided during the task. ERPs were time-locked to tactile stimuli and extracted for early modality-specific components (P50, P100, N140). The P50 was enhanced with bimodal (visual-tactile) stimuli that were attended to. This was maximal when the motor requirements involved integration of the 2 stimuli in the grade task and when the visual stimulus occurred before (100 ms) the tactile stimulus. These results suggest that visual information relevant for movement modulates early somatosensory processing and that the motor behavioral context influences this likely through interaction of top-down attentional and motor preparatory systems with more bottom-up crossmodal influences.
Frontiers in Psychology 04/2014; 5:351. DOI:10.3389/fpsyg.2014.00351 · 2.80 Impact Factor
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