Sensory mapping in a congenitally deaf subject: MEG and fRMI studies of cross-modal non-plasticity

It has been proposed that the auditory cortex of deaf subjects may provide an example of cross-modal compensatory plasticity. We investigated whether sensory stimulation could elicit responses from auditory areas of a congenitally deaf subject. Neuromagnetic fields were recorded using a 37-channel biomagnetometer under conditions of: 1) visual stimulation; 2) somatosensory stimulation; and 3) a simple motor task. Visual items were reversing checkerboards and single light spots, presented in various portions of the visual field; somatosensory stimuli were pneumatic taps delivered to individual digit-segments and the lip; the motor task was self-paced finger tapping. In addition, functional magnetic resonance imaging was used to observe the activation elicited by full-field checkerboard and sign language stimuli. No responses to passively presented visual or somatosensory stimuli were observed in the auditory cortex. In contrast, somatosensory, motor, and visual cortices revealed evoked magnetic responses comparable to those from control subjects, indicating canonical anatomic and physiological organization in these areas. These data suggest that primary projection areas do not reveal obvious plastic effects. We suggest that in the human auditory cortex compensatory plasticity emerges primarily as a property of non-primary areas and is best observed under attentionally demanding conditions.