Hearing Loss and Age-Induced Changes in the Central Auditory System Measured by the P3 Response to Small Changes in Frequency.

Abstract

Recent behavioral studies have suggested that individuals with sloping audiograms exhibit localized improvements in frequency discrimination in the frequency region near the drop in hearing. Auditory-evoked potentials may provide evidence of such cortical plasticity and reorganization of frequency maps. The objective of this study was to evaluate electrophysiological evidence of cortical plasticity related to cortical frequency representation and discrimination abilities in older individuals with high-frequency sensorineural hearing loss (SNHL). It was hypothesized that the P3 response in this group would show evidence of physiological reorganization of frequency maps and enhanced neural representation at the edge of their high-frequency loss due to their restricted SNHL. The P3 auditory event-related potential in response to small frequency changes was recorded in a repeated measures design using an oddball paradigm that presented upward and downward frequency changes of 2%, 5%, and 20% to three groups of listeners. P3 recordings from a group of seven older individuals with a restricted sloping hearing loss >1000 or 2000 Hz was compared to two control groups of younger (n = 7) and older (n = 7) individuals with normal hearing/borderline normal hearing through 4000 Hz. The auditory P3 was recorded using an oddball paradigm (80%/20%) with the standard tone at the highest frequency of normal hearing in the hearing-impaired participants, also known as the edge frequency (EF). EFs were either 1000 or 2000 Hz for all participants. The target tones represented upward and downward frequency changes of 2%, 5%, and 20% from the standard tones of either 1000 or 2000 Hz. Waveforms were recorded using a two-channel clinical-evoked potential system. Latency and amplitude of the P300 peak were analyzed across groups for the three frequency conditions using repeated measures analysis of variance. The results of this study suggest that the P3 response can be elicited by frequency changes as small as 2-5%. P3 responses at the EF of hearing loss were present and larger in amplitude for more participants with a sloping hearing loss compared to age-matched normal-hearing peers tested at the same frequencies. As a result, the older participants with sloping hearing losses had P3 responses more similar to the younger normal-hearing participants than their age-matched peers with normal hearing. These preliminary results partially support the idea of enhanced cortical representation of frequency at the EF of localized SNHL in older adults that is not purely due to age.