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 been 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 deprivation. CNS activity was assessed by measuring long-latency auditory evoked potentials (AEPs) recorded from teens and adults with late-onset (post-childhood) profound unilateral deafness. Compared to monaurally stimulated normal-hearing subjects, the AEPs recorded from central electrode sites located over auditory cortical areas showed significant increases in inter-hemispheric waveform cross-correlation coefficients, and in inter-hemispheric AEP peak amplitude correlations. These increases provide evidence of substantial changes from the normal pattern of asymmetrical (contralateral > ipsilateral amplitude) and asynchronous (contralateral earlier than ipsilateral) central 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 also suggest that the changes in cortical activity occur gradually and continue for at least 2 years after the onset of hearing loss. Analyses of peak amplitude correlations suggest that the increased inter-hemispheric symmetry may be a consequence of changes in the generators producing the N (approximately 100 ms peak latency) potential. These experience-related changes in central auditory system activity following late-onset profound unilateral deafness thus provide evidence of the presence and the time course of auditory system plasticity in the adult brain.
Ponton
C W
CW
Electrophysiology Laboratory, House Ear Institute, Los Angeles, CA 90057, USA. cponton@neuroscan.com
Vasama
J P
JP
Tremblay
K
K
Khosla
D
D
Kwong
B
B
Don
M
M
D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D001303:Auditory Cortex / Q000503:physiopathology*; D016022:Case-Control Studies; D003638:Deafness / Q000503:physiopathology*; D005072:Evoked Potentials, Auditory; D006801:Humans; D008875:Middle Aged; D009473:Neuronal Plasticity; D013017:Sound Localization