Plasticity in the adult human central auditory system: evidence from late-onset profound unilateral deafness

Experience-related changes in central nervous system (CNS) activity have be en observed in the adult brain of many mammalian species, including humans. In humans, late-onset profound unilateral deafness creates an opportunity to study plasticity in the adult CNS consequent to monaural auditory depriv ation. CNS activity was assessed by measuring long-latency auditory evoked potentials (AEPs) recorded from teens and adults with late-onset (post-chil dhood) profound unilateral deafness. Compared to monaurally stimulated norm al-hearing subjects, the AEPs recorded from central electrode sites located over auditory cortical areas showed significant increases in inter-hemisph eric waveform cross-correlation coefficients. and in inter-hemispheric AEP peak amplitude correlations. These increases provide evidence of substantia l changes from the normal pattern of asymmetrical (contralateral > ipsilate ral amplitude) and asynchronous (contralateral earlier than ipsilateral) ce ntral auditory system activation in the normal-hearing population to a much more symmetrical and synchronous activation in the unilaterally deaf These cross-sectional analyses of AEP data recorded from the unilaterally deaf a lso suggest that the changes in cortical activity occur gradually and conti nue for at least 2 years after the onset of hearing loss. Analyses of peak amplitude correlations suggest that the increased inter-hemispheric symmetr y may be a consequence of changes in the generators producing the N-1 (appr oximately 100 ms peak latency) potential. These experience-related changes in central auditory system activity following late-onset profound unilatera l deafness thus provide evidence of the presence and the time course of aud itory system plasticity in the adult brain. (C) 2001 Elsevier Science B.V. All rights reserved.