Friday, Sep 11, 2015
Auditory processing in ageing: evidence for the inhibitory deficit hypothesis
School of Experimental Psychology, University of Bristol, Bristol, United Kingdom
We investigated the effects of ageing on auditory processing in 20 younger adults (aged 18-23, mean age 20 (±2), 5 males) and 26 older adults (aged 62-88, mean age 76 (±7)) who listened to syllables presented at 60dB above the participant’s hearing threshold in an auditory-only or audiovisual oddball paradigm. Older adults showed increased early sensory responses (i.e. increased P50 and N100 amplitudes compared to younger adults) followed by an absence of a standard N2 response; the MMN was not affected by age. A similar pattern was observed in the control puretone condition (200 repetitions of a 1kHz tone) when the sound volume was kept the same across participants.
We propose that the increased early P50 and N100, followed by the absence of a standard N2 provides evidence for the Inhibitory Deficit Hypothesis of ageing (IDH) theory whereby declines in auditory processing are a result of age-related inefficiency of the fronto-cortical areas in inhibiting irrelevant information. Reduced ability of the frontal lobes to inhibit and regulate the primary sensory areas results in increased responses from these areas (P50 and N100). N2 is typically observed in response to stimuli that involve inhibitory processing (e.g. ignoring the standard stimulus in an oddball task or not responding to the no-go stimulus in a go/no-go task), hence its absence in older individuals matches the predictions by the IDH. We discuss theoretical significance of a preserved MMN in ageing.