Cross-modal plasticity for tactile and auditory stimuli within the visual cortex of early blind human subjects

A number of studies have demonstrated cross-modal responses within visual cortex as a result of blindness. However, little is known about the organizational principles that drive cross-modal plasticity. One possibility is that cross-modal plasticity in visual cortex is pluripotent - cross-modal responses in visual cortex may not show strong selectivity for either modality or task. Alternatively, if cross-modal plasticity is driven by functional specificity, similar activations might be expected for a given task, regardless of modality; whereas if cross-modal plasticity is driven by anatomical connectivity between visual cortex and other sensory cortical areas, similar activations might be expected for a given modality, regardless of task. Here we present work from two studies. In the first study, fMRI responses to a variety of tasks in auditory and tactile modalities were measured in early blind and sighted subjects. We found cross-modal plasticity (greater fMRI responses in blind than sighted subjects) in visual cortex for all tasks, with many areas showing cross-modal plasticity for all the tasks that we tested - across much of cortex the degree of specialization underlying cross- modal plasticity seems to be relatively weak (pluripotency). However, in dorsal-occipital and ventral regions of visual cortex, we did find evidence for selectivity based on modality (greater response to tactile than auditory tasks), and in occipital-temporal regions of cortex we found modulation of cross-modal response by task. In our second study we specifically tested the functional specificity hypothesis in visual motion area MT +. To more accurately define MT+, we used two rare sight- recovery subjects. In these subjects MT+ responded to auditory motion, while in visually normal subjects MT+ did not show similar auditory responses. These auditory responses in MT+ were specific to motion compared with other complex auditory stimuli, suggesting that cross- modal plasticity can be influenced by the normal functional specialization of a cortical region. Our results further demonstrate that in the case of sight recovery, cross-modal responses can coexist with regained visual responses within the visual corte