Multisensory stimulation with or without saccades: fMRI evidence for crossmodal effects on sensory-specific cortices that reflect multisensory location-congruence rather than task-relevance

During covert attention to peripheral visual targets, presenting a concurrent tactile stimulus at the same location as a visual target can boost neural responses to it, even in sensory-specific occipital areas. Here, we examined any such crossmodal spatial-congruence effects in the context of overt spatial orienting, when saccadic eye-movements were directed to each peripheral target or central fixation maintained. In addition, we tested whether crossmodal spatial-congruence effects depend on the task-relevance of visual or tactile stimuli. On each trial, subjects received spatially congruent (same location) or incongruent (opposite hemifields) visuo-tactile stimulation. In different blocks, they made saccades either to the location of each visual stimulus, or to the location of each tactile stimulus; or else passively received the multisensory stimulation. Activity in visual extrastriate areas and in somatosensory parietal operculum was modulated by spatial congruence of the multisensory stimulation, with stronger activations when concurrent visual and tactile stimuli were both delivered at the same contralateral location. Critically, lateral occipital cortex and parietal operculum showed such crossmodal spatial effects irrespective of which modality was task relevant; and also of whether the stimuli were used to guide eye-movements or were just passively received. These results reveal crossmodal spatial-congruence effects upon visual and somatosensory sensory-specific areas that are relatively 'automatic', determined by the spatial relation of multisensory input rather than by its task-relevance.