In sensory substitution, information acquired with one sensory modality is use d to accomplish a task which is normally subserved primarily by another sensory modality. We used PET to study cross-modal plasticity in the congenitally blind , using electrotactile stimulation of the tongue. Blind (n=6) and sighted blindfolded controls (n=5) were scanned before and after they were trained to use their tongue in a Snellen orientation detect ion task. Results showed that both groups of subjects learned the discrimination orientation task after seven 1 h training sessions. Before training, no signifi cant changes in regional cerebral blood flow (rCBF) were observed in the occipit al cortex in either group. In sharp contrast, activity in the occipital cortex i ncreased after practice for the blind, but not for the sighted, providing eviden ce for training-induced plasticity in the blind. An inter-regional correlation analysis showed that task-related rCBF changes in left posterior parietal cort ex were positively correlated with rCBF changes in the occipital area of the tra ined blind. These data reveal that cross-modal plasticity in the blind develops rapidly and that the occipital cortex is part of a functional neural network fo r tactile discrimination in conjunction with the posterior parietal cortex. Our data further show that the tongue can act as a portal to convey somatosensory in formation to visual cortex. In sensory substitution, information acquired with one sensory modality is use d to accomplish a task which is normally subserved in by another sensory modality. We used PET to study cross-modal plasticity in the congenitally blind, using electrotactile stimulation of the tongue. Blind ( n = 6) and sighted blindfolded controls (n = 5) were scanned before and after they were trained to use their tongue in a Snellen orientation detect ion task. Results showed that both learned individuals who learned the discrimination orientation task after seven 1 h training sessions before training, no signifi cant changes in regional cerebral blood flow (rCBF) were observed in the occipit al cortex in either group. In sharp contrast, activity in the occipital cortex i ncreased after practice for the blind, but not for the sighted , providing eviden ce for training-induced plasticity in the blind. An inter-regional correlation analysis showed that task-related rCBF changes in left posterior parietal cor t ex were positively correlated with rCBF changes in the occipital area of ​​the trained blind. These data reveal that cross-modal plasticity in the blind develops rapidly and that the occipital cortex is part of a functional neural network fo r tactile discrimination in conjunction with the posterior parietal cortex. Our data further show that the tongue can act as a portal to convey somatosensory in formation to visual cortex.