Abstract
A key signature of neural development is that the brains of children have a greater capacity for recovery following damage or surgery than adults. Indeed, children who have had an entire hemisphere of their brain removed to treat epilepsy (a procedure known as hemispherectomy) show a high degree of perceptual functioning despite the loss of both ventral and dorsal visual pathways in one hemisphere. Yet, accumulating evidence suggests that the dorsal pathway may mature earlier than the ventral pathway – raising the question of whether the two pathways also have a different capacity for recovery after surgery. In the current study, we sought to understand the extent to which functions of the ventral and dorsal pathways reorganize to the contralateral hemisphere following childhood hemispherectomy. We collected fMRI data from an equal number of left and right hemispherectomy patients (N = 8; age-at-surgery = 1-13 years; age-at-testing = 12-37 years) who completed tasks that typically elicit lateralized responses from the ventral or the dorsal pathway in controls, namely, word (left ventral), face (right ventral), tool (left dorsal), and global form (right dorsal) perception. Overall, there was greater evidence of functional reorganization in the ventral pathway than in the dorsal pathway. The majority of hemispherectomy patients showed normal degrees of word and face selectivity in their intact ventral pathway, despite losing the typically preferred hemisphere for each category. By contrast, only one patient showed evidence of normal selectivity for either tools or global form in their intact dorsal pathway. Importantly, because ventral and dorsal reorganization was tested within the same patients, these results cannot be explained by idiosyncratic factors such as disease etiology or age at the time of surgery. These findings suggest that the dorsal pathway has a shorter developmental window of plasticity than the ventral pathway because it matures earlier.