Abstract
Neuroplasticity is a fundamental property of the developing mammalian visual system. A short period of abnormal visual experience during the critical period, such as occlusion of one eye, has dramatic and permanent neural consequences, reshaping visual cortical organization in favour of the non-deprived eye. After closure of the critical period, the brain is thought to be relatively hard-wired, with little or no experience-dependent plasticity. Using binocular rivalry – a sensitive probe of neural competition – we demonstrate that adult human visual cortex retains an unexpectedly high degree of neural plasticity, with important perceptual consequences. Following a brief (150 min) period of monocular deprivation, during which observers wore a translucent eyepatch on one eye, orthogonally oriented gratings (horizontal-vertical, S.F. 3 cpd, contrast 0.75) were presented separately to the two eyes through FE-Shuttering Goggles and observers reported their rivalrous visual perception by continuous keypress. Monocular deprivation strongly affected the dynamics of binocular rivalry, unexpectedly causing the deprived eye to dominate conscious perception twice as often as the non-deprived eye (mean phase duration of the deprived eye increased on average of the 53%, mean duration of the non deprived eye decreased on average of the 24%), and prevailing for as long as 90 minutes. Stimuli viewed by the deprived eye also appeared of higher contrast than those viewed by the other, as assessed by an apparent contrast matching procedure. We suggest that the deprivation acts by up-regulation of cortical gain-control mechanisms of the deprived eye, either by decreasing intracortical inhibition or increasing excitation. These results call for a revaluation of adult visual cortical plasticity, fundamental to understanding how the adult visual system reacts to sensory loss, and for developing new therapeutic strategies that exploit the intrinsic plasticity of the visual cortex.