The effect of task-relevance on primary somatosensory cortex during continuous sensory-guided movement in the presence of bimodal competition.

Recent perceptual neuroimaging studies have shown that intermodal selective attention extracts relevant information from one modality at the expense of another at the level of unimodal sensory cortex. The present paper sought 1) to determine the effects of intermodal selective attention on primary somatosensory cortex (S1) during continuous sensorimotor transformations, 2) to investigate the interactions of spatial relationship between the target and distracter modalities on S1 and 3) to identify any potential modulators during continuous sensorimotor transformations. Functional MRI was acquired while participants (n=10) received simultaneous vibrotactile and visuospatial stimulation. In each condition, participants tracked either vibrotactile stimulation (25 Hz), applied to the right index finger with variable intensity, or a visuospatial stimulus, a centrally presented dial where the spatial position of a needle randomly moved, by applying graded force to a force sensing resistor. The distracter modality either originated from a location that was spatially related or distinct to the target that guided movement. Vibrotactile tracking resulted in decreased S1 activation relative to when it was task-irrelevant. Neither S1 activity nor tracking performance was influenced by spatial relationship. In addition the superior parietal lobe/precuneus (BA 7), inferior parietal lobe (BA 40), precentral gyrus (BA 6) and secondary visual areas (BA 18 and 19) may modulate the extraction of task-relevant information while the insula (BA 13) may do so during cases of spatial conflict. We conclude that modulation of S1 is important to the proper execution of sensory-guided movements and that sensorimotor requirements determine the mechanisms of intermodal selective attention.