Dr. Daniel Dilks
Many electrophysiological studies have reported plasticity (or “reorganization”) in primary visual cortex (V1) in adult animals: after lesioning the retina, the region of V1 deprived of bottom-up input begins to respond to stimuli that normally activate adjacent cortex only. However, the time course, underlying mechanisms, and even the very existence of this reorganization are matters of intense controversy. Moreover, adult cortical reorganization has not been well documented in the human visual system; nor have animal or human studies explored whether reorganization affects visual perception. Here I report data from patients with deprived early visual cortex, and a consequent blind area (i.e., due to stroke and macular degeneration). Behavioral and fMRI experiments provide a clear demonstration of cortical reorganization in the adult human visual system, and the first evidence that reorganization affects visual perception (e.g., a square presented adjacent to the blind area is perceived as a rectangle). To investigate the time course of such reorganization, I developed a novel perceptual paradigm to deprive a region of early visual cortex in people with normal vision. I provide evidence that after only seconds of such deprivation distorted perception occurs (squares are perceived as rectangles). This result demonstrates that reorganization can occur very rapidly in adult retinotopic cortex, and implicates unmasking of pre-exisiting connections as the underlying mechanism. Taken together, these findings contribute to our understanding of the human adult brain’s capacity to change, and have implications for fundamental topics such as development, learning, and recovery from brain damage.
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