| This study was designed to investigate the functional and organizational differences in the auditory cortices of congenitally deaf signing subjects, hearing signing (HS) subjects who have deaf parents, and hearing non-signing (HNS) subjects. During the course of the project, 15 subjects, of whom 5 were Deaf, 4 HS, and 6 HNS, were administered a neuropsychological test battery of visual and cognitive functioning. The results of the neuropsychological test battery did not suggest that any of the subjects had significant pathology that could have interfered with the results of the functional brain imaging. Further, the results did not indicate differences in intellectual and cognitive functioning between the three groups of subjects. In order to investigate for evidence of cross-modal plasticity, the ability of the brain to reorganize itself in the event that one of the body's sensory modalities is nonfunctional, the neural activity of the subjects was assessed through the use of structural magnetic resonance imaging (sMRI), functional MRI (fMRI), and magnetoencephalography (MEG). During the measurement of cortical activation through each of these brain-imaging techniques, the subjects were presented with a vibrotactile stimulus, a visual motion stimulus, and a sign language stimulus. The fMRI data yielded results that were ambiguous and inconclusive. Additionally, the software used to analyze the MEG results was not able to provide accurate interpretation of the data acquired with the sign language stimulus. However, the MEG results for the vibration and visual motion stimuli displayed tentative evidence suggesting cross-modal plasticity of the auditory cortex in some of the subjects. The results from all of the deaf subjects and from one of the HS subjects indicated cross-modal plasticity of the auditory cortex for functions other than hearing while the results from the HNS subjects did not. This suggests that congenital deafness and use of sign language from an early age may lead to functional changes of the auditory cortex. |
