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.
- SourceAvailable from: Christina Popovich
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- "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. "
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).Brain and Behavior 03/2014; 4(2):247-60. DOI:10.1002/brb3.210
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- "One likely structure responsible for setting the " sensory vigilance " is the prefrontal cortex. This region is known to project toward the sensorimotor cortex (Christensen et al. 2007; Jones 1986) and to regulate the transmission of sensory inputs to primary sensory areas according to their task relevance (Knight et al. 1999; Staines et al. 2002; Yamaguchi and Knight 1990). This function of the frontal lobe is also supported by the fact that patients with damage to the prefrontal cortex fail to distinguish between relevant and irrelevant sensory information (Knight et al. 1999). "
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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- "All subjects received the same instructions to maximize the feedback signal using any hand imagery strategy, and subjects were not aware that the signal reflected a laterality index. The observed results are consistent with reported findings of suppressed ipsilateral M1 activity in a study of dynamic interhemispheric interactions during unilateral hand movement (Grefkes et al., 2008), and are similar to the top-down inter-hemispheric sensory gating effects observed in studies of somatosensation (Staines et al., 2002). Previous studies of laterality and motor imagery have shown ipsilateral activations to be present during unilateral imagery (Porro et al., 2000). "
ABSTRACT: Functional MRI neurofeedback (fMRI NF) is an emerging technique that trains subjects to regulate their brain activity while they manipulate sensory stimulus representations of fMRI signals in "real-time". Here we report an fMRI NF study of brain activity associated with kinesthetic motor imagery (kMI), analyzed using partial least squares (PLS), a multivariate analysis technique. Thirteen healthy young adult subjects performed kMI involving each hand separately, with NF training targeting regions of interest (ROIs) in the left and right primary motor cortex (M1). Throughout, subjects attempted to maximize a laterality index (LI) of brain activity-the difference in activity between the contralateral ROI (relative to the hand involved in kMI) and the ipsilateral M1 ROI-while receiving real-time updates on a visual display. Six of 13 subjects were successful in increasing the LI value, whereas the other 7 were not successful and performed similarly to 5 control subjects who received sham NF training. Ability to suppress activity in the ipsilateral M1 ROI was the primary driver of successful NF performance. Multiple PLS analyses depicted activated networks of brain regions involved with imagery, self-awareness, and feedback processing, and additionally showed that activation of the task positive network was correlated with task performance. These results indicate that fMRI NF of kMI is capable of modulating brain activity in primary motor regions in a subset of the population. In the future, such methods may be useful in the development of NF training methods for enhancing motor rehabilitation following stroke.NeuroImage 03/2012; 61(1):21-31. DOI:10.1016/j.neuroimage.2012.02.053 · 6.36 Impact Factor