Evidence for greater sight in blindsight following damage of primary visual cortex early in life

This review compares the behavioral, physiological and anatomical repercussions of lesions of primary visual cortex incurred by developing and mature humans, monkey and cats. Comparison of the data on the repercussions following lesions incurred earlier or later in life suggests that earlier, but not later, damage unmasks a latent flexibility of the brain to compensate partially for functions normally attributed to the damaged cortex. The compensations are best documented in the cat and they can be linked to system-wide repercussions that include selected pathway expansions and neuron degenerations, and functional adjustments in neuronal activity. Even though evidence from humans and monkeys is extremely limited, it is argued on the basis of known repercussions and similarity of visual system organization and developmental sequence, that broadly equivalent repercussions most likely occur in humans and monkeys following early lesions of primary visual cortex. The extant data suggest potentially useful directions for future investigations on functional anatomical aspects of visual capacities spared in human patients and monkeys following early damage of primary visual cortex. Such research is likely to have a substantial impact on increasing our understanding of the repercussions that result from damage elsewhere in the developing cerebral cortex and it is likely to contribute to our understanding of the remarkable ability of the human brain to adapt to insults.