Abstract:

Blindness provides an unparalleled opportunity to study plasticity of the nervous system in humans. Seminal work in this area examined the often dramatic modifications to the visual cortex that result when visual input is completely absent from birth or very early in life. Our lab and others have demonstrated that decreases in visual pathway integrity occur in those with acquired blindness. More recent studies have begun to examine the changes occurring with certain disease states: patients suffering from optic neuritis secondary to multiple sclerosis and glaucoma, all so far demonstrate deterioration of the white matter tract architecture as a function of disease severity. This leads to the conclusion that the visual system as a whole is profoundly susceptible to degeneration even with small amounts of vision loss. On the surface, these investigations appear to have dire implications for vision restoration efforts. Yet, parallel studies which examine the phenomenon of cross-modal plasticity suggest that a remodeling of the central nervous system is possible, such that areas of the brain which have been deprived of normal afferent input are able to reconstitute themselves to be receptive to alternative sensory channels. The literature is rife with examples of investigations which show that the visual cortex will react to tactile and auditory stimuli in the blind but will be less readily recruited in sighted patients. Moreover, cross-modal interactions have been demonstrated well beyond the traditional “critical period” and into late adulthood, albeit perhaps in a less robust fashion. The notion that the adult brain is still capable of significant structural and functional remodeling after vision loss remains a beacon of hope for researchers and patients alike who dream of recovering vision through mechanical or biological means.