Plasticity Within Sensory and Language Systems: The Role of Experience

Hypothesis

Hypothesis

Hypothesis:
1. Potential for plasticity is expected to differ across brain systems, as a result of different developmental timecourse, patterns of connections, and molecular mechanisms.

2. Plasticity is expected to consist in functionally specialized changes in the brain systems in which they occur.

Goals:
The goal of this study is to characterize the role of early experience on the organization of the adult brain in humans. To address this issue, researchers are studying the brain organization of congenitally deaf individuals. Their first aim concerns the impact of auditory loss on visual functions. Does the auditory cortex reorganize in deaf individuals to process visual information? Their second aim concerns the impact of learning a visuo-spatial language such as American Sign Language (ASL) on the cerebral organization for language. Does ASL engage mainly the left hemisphere like spoken languages, or rather the right hemisphere like all other visuo-spatial tasks?

Methods:
The physiology of sensory and language processing will be studied using the brain imaging technique of functional magnetic resonance imaging (fMRI). This technique involves recording indices of brain activity while subjects perform different visual or language tasks.

Four different populations will be compared to a control population of young adults: (a) congenitally deaf individuals born to deaf parents and who have learned ASL as a first language from their deaf parents, (b) later-deafened individuals who acquire ASL as a first language from their deaf parents, (c) hearing Ss born to deaf parents and who acquire ASL as a first language, and (d) hearing ASL interpreters who acquire ASL after 18 years of age. These subjects will also be healthy, right-handed males and females between 20 and 35 years of age.

Follow-on Funding:
The David and Lucile Packard Foundation RO1-NIDCD

Findings:
Deafness leads to extremely specific changes, such that only limited aspects of visual functions are modified in deaf individuals. One such function is the distribution of visual attention over space. Deaf individuals exhibit enhanced peripheral visual attention, especially for moving stimuli. These behavioral changes are accompanied by a reorganization of brain areas know to act as convergence zones between the different senses. Our research supported the view that, in the absence of one modality, the remaining modalities take over multi-modal cortices, allowing for compensatory plasticity.