title: Age-related changes in the subcortical-cortical encoding and categorical perception of speech.
abstract: Aging is associated with declines in auditory processing including speech comprehension abilities. Here, we evaluated both brainstem and cortical speech-evoked brain responses to elucidate how aging impacts the neural transcription and transfer of speech information between functional levels of the auditory nervous system. Behaviorally, older adults showed slower, more variable speech classification performance than younger listeners, which coincided with reduced brainstem amplitude and increased, but delayed, cortical speech-evoked responses. Mild age-related hearing loss showed differential correspondence with neurophysiological responses showing negative (brainstem) and positive (cortical) correlations with brain activity. Spontaneous brain activity, that is, "neural noise," did not differ between older and younger adults. Yet, mutual information and correlations computed between brainstem and cortex revealed higher redundancy (i.e., lower interdependence) in speech information transferred along the auditory pathway implying less neural flexibility in older adults. Results are consistent with the notion that weakened speech encoding in brainstem is overcompensated by increased cortical dysinhibition in the aging brain. Findings suggest aging negatively impacts speech listening abilities by distorting the hierarchy of speech representations, reducing neural flexibility through increased neural redundancy, and ultimately impairing the acoustic-phonetic mapping necessary for robust speech understanding.
authors.affiliation: Institute for Intelligent Systems, University of Memphis, Memphis, TN, USA; School of Communication Sciences & Disorders, University of Memphis, Memphis, TN, USA. Electronic address: g.bidelman@memphis.edu.
authors.forename: Gavin M
authors.initials: GM
authors.lastname: Bidelman
authors.affiliation: Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada; Department of Psychology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Joshua W
authors.initials: JW
authors.lastname: Villafuerte
authors.affiliation: Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada; Department of Psychology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Moreno
authors.affiliation: Rotman Research Institute, Baycrest Centre for Geriatric Care, Toronto, Ontario, Canada; Department of Psychology, University of Toronto, Toronto, Ontario, Canada; Institute of Medical Sciences, University of Toronto, Ontario, Canada.
authors.forename: Claude
authors.initials: C
authors.lastname: Alain
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001306:Auditory Pathways / Q000502:physiology / Q000503:physiopathology; D001933:Brain Stem / Q000502:physiology / Q000503:physiopathology; D002540:Cerebral Cortex / Q000502:physiology* / Q000503:physiopathology; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D006801:Humans; D008875:Middle Aged; D013067:Speech Perception / Q000502:physiology*; D055815:Young Adult
keywords: Auditory event-related potentials (ERPs); Brain signal variability; Brainstem frequency-following response (FFR); Categorical speech perception; Cognitive aging; Mutual information (MI); Speech perception