Neural Deterioration and Cross-modal Plasticity in the Blind

Lay Summary

Using Imaging to Learn How to Maximally Restore Visual Functioning

Using MRI and fMRI in people who are blind at an early age and those who became blind later in life, the researchers will study how visual deprivation affects the visual cortex and how brain plasticity affects the cortex’s responses to non-visual senses. The results may improve approaches for restoring visual function following use of emerging therapeutic advances, such as corneal and retinal transplants, gene therapy, and retinal prostheses.

Animal model research has shown that when sensory deprivation (such as blindness) occurs early, rather than later in life, there is a greater disruption of neuronal organization.  Additionally, when the sensory cortex is deprived early in life, it is more responsive to other senses, according to both animal and human studies. This adaptive process is called “cross-modal” plasticity.  The researchers will determine how neuronal deterioration caused by losing vision is related to this cross-modal plasticity.  They will use MRS to identify biomarkers of neuronal deterioration in healthy participants and in people who were blind early compared to those who became blind in adulthood. Then the researchers will use fMRI in the three participant groups to measure neural activity in response to auditory and tactile stimuli within the visual cortex.

The investigators hypothesize that cross-modal plasticity may provide an alternative form of sensory input that helps to prevent neural deterioration in the absence of vision.  If this is the case, they will find less neuronal deterioration in patients who were blind early, and for a longer time, than people who became blind in adulthood.

Significance: If this research shows that early cross-modal plasticity helps to spare neuronal degeneration, parents of blind children may be more willing to encourage their children to read Braille and use a cane.  Moreover, this use of other sensory modalities to help preserve neurons in the visual cortex in turn may help improve the outcomes of evolving therapies, such as corneal and retinal transplants.

Abstract

Neural Deterioration and Cross-modal Plasticity in the Blind

Numerous brain-imaging studies have found responses to tactile and auditory stimuli in the visual cortex of blind subjects. It seems that losing a sense early in life leads to a sensory reorganization whereby visual cortex (if sight is restored), shows a deterioration in processing visual information, and begins to process information from other senses. This cross-modal plasticity is thought to play an important role in helping blind subjects perform well on complex tactile and auditory tasks, such as reading Braille and orienting themselves using the sound of a tapping cane. We propose:

(1) To measure changes in brain metabolites in early visual cortex as a result of visual deprivation.

(2) To test whether cross-modal plasticity may maintain neuronal function (and connectivity) within cortical areas that would otherwise be silent and susceptible to neural degeneration.