Cross-modal Reorganization Of Auditory Cortex In Deaf:an FMRI Study

Visual stimulus activates the auditory cortex of deaf persons, showing the evidence of cross-modal plasticity. However, the underlying mechanisms of such plasticity are poorly understood. In this study, using functional magnetic resonance imaging(fMRI), we presented four types of visual stimuli (language-related stimulus:word, sign language (SL) and lip-reading; non-language control:checkerboard) and investigated the neural connectivity of reorganized auditory cortex in normal hearing controls and in two groups of deaf subjects, who are either full deaf or residual deaf with hearing aid.We found that all visual stimuli activated auditory cortex in deaf, but not in normal hearing subject except in lip-reading condition. Interestingly, the spatial pattern of reorganization activation in auditory cortex was significantly more similar within the language stimuli than between checkerboard and language stimulus.Functional connectivity analysis revealed that the sources of this cross-modal reorganization mainly included two pathways:feedforward connections from thalamus and visual cortex (vision-driven) and feedback connections from anterior temporal cortex (language-driven).Further, the cross-model activation in deaf auditory cortex induced by checkerboard was positively correlated with duration of deafness and not with onset of SL learning, indicating the consequence of sensory deprivation. In the contrast, the auditory activations provoked by sign language was highly positive correlated with the onset of SL learning but not with duration of deafness, suggesting the strong top-down modulation effect of language-experience on the cross-modal reorganization. Meanwhile, functional connectivity between auditory cortex and SMA(Somatic Motor Cortex) were positively correlated with duration of deafness by checkerboard, however, visual cortex and auditory cortex were highly positive correlated with the onset of SL learning, auditory cortex and frontal cortex were highly negative correlated with the onset of SL learnin by language stimuli, suggesting regarding visual information to language information by language experience.Taken together, the present study showed the differences of neural networks between hearing and deaf individuals, and between visual stimuli with or without language content, and provided important and unique evidence for understanding neural circuits of cross-modal plasticity in deaf.