Dissociable crossmodal recruitment of visual and auditory cortex for tactile perception

Primary sensory areas previously thought to be devoted to a single modality can exhibit multisensory responses. Some have interpreted these responses as evidence for crossmodal recruitment (i.e., primary sensory processing for inputs in a non-primary modality); however, the direct contribution of this activity to perception is unclear. We tested the specific contributions of visual and auditory cortex to tactile perception in healthy adult volunteers using anodal transcranial direct current stimulation (tDCS). This form of non-invasive neuromodulation can enhance neural excitability and facilitate learning. In a series of psychophysical experiments we characterized participants’ ability to discriminate grating orientation or vibration frequency. We measured perceptual sensitivity before, during, and after tDCS application over either visual cortex or auditory cortex. Each participant received both anodal and sham interventions on separate sessions in counterbalanced order. We found that anodal stimulation over visual cortex selectively improved tactile spatial acuity, but not frequency sensitivity. Conversely, anodal stimulation over auditory cortex selectively improved tactile frequency sensitivity, but not spatial acuity. Furthermore, we found that improvements in tactile perception persisted after cessation of tDCS. These results reveal a clear double-dissociation in the crossmodal contributions of visual and auditory cortex to tactile perception, and support a supramodal brain organization scheme in which visual and auditory cortex comprise distributed networks that support shape and frequency perception, independent of sensory input modality.