Human Adult Cortical Reorganization and Consequent Visual Distortion

Danny Dilks

Kanwisher Lab, McGovern Institute for Brain Research, MIT

The adult brain exhibits a remarkable degree of plasticity, or does it?  Cortical plasticity (or reorganization) in the adult visual system has principally been demonstrated in studies of non-human animals:  If a region of primary visual cortex (V1) loses its usual input (e.g., due to retinal damage), neurons in that region begin responding to stimuli that normally activate adjacent V1 cortex.  However, recent controversy has arisen concerning whether cortical reorganization occurs in the adult animal visual system.  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).  Additionally, I ask how quickly this reorganization and perceptual distortion can happen.  Using a novel perceptual paradigm by which I deprived a region of early visual cortex in normals, I provide evidence that after only ten minutes of such deprivation distorted perception occurs (squares are perceived as rectangles). These findings contribute to our understanding of the human adult brain’s capacity to change, and has implications for topics ranging from learning to recovery from brain damage.