Although some brain areas preferentially process information from a particular sensory modality, these areas can also respond to other modalities (1-5). We used fMRI to show that such responsiveness to tactile stimuli depends on the temporal frequency of stimulation. Participants performed a tactile threshold-tracking task where the tip of either their left or right middle finger was stimulated at 3, 20, or 100 Hz. Whole-brain analysis revealed an effect of stimulus frequency in two regions: the auditory cortex and the visual cortex. The BOLD response in the auditory cortex was stronger during tactile stimulation at hearable frequencies (20 and 100 Hz) whereas the response in the visual cortex was suppressed at infrasonic frequencies typical of biological motion (3 Hz). Regardless of which hand was stimulated, the frequency dependent effects were lateralized to the left auditory cortex and the right visual cortex. Furthermore, the frequency-dependent effects in both areas were abolished when the participants performed a visual task while receiving identical tactile stimulation as in the tactile threshold-tracking task. Our findings advance the metamodal theory of brain function (6) by showing that changing input to a single sensory modality in the context of the same task can affect BOLD activity in two unimodal cortical areas primarily associated with processing other sensory modalities. That is, brain areas contribute to sensory processing by performing specific computations regardless of input modality.

Human, Touch, Auditory Cortex, Visual Cortex, Somatosensory Cortex