Aging-related changes in processing of non-target and target stimuli during an auditory oddball task.

A total of 73 healthy subjects aged 20-86 years performed an auditory 'oddball' task. The age-dependence of N1 and P2 elicited by non-target stimuli, of N2 and P3 elicited by target stimuli and of N2a and N2b components (target minus non-target difference waves) was investigated across 20 electrodes to detect any aging-related changes in the psychophysiological processing of such stimuli during the task. Aging-related differences in within-task changes in non-target ERPs were also investigated. In non-target ERPs, it was found that P2 amplitude at Fz increased linearly with advancing age and the analysis of within-task changes indicated that P2 amplitude decreased during the task in young subjects at Pz, but remained unchanged in middle-aged and elderly subjects. These results suggest the existence of aging-related inhibitory deficits that may hinder the disengagement of attentional resources from irrelevant stimuli during the task. In the target ERPs, the latencies of N2 and P3 increased linearly at Fz, Cz and Pz. The increases in N2 were mainly due to linear increases in N2b latency at Fz, Cz and Pz, indicating that the aging-related slowing begins at controlled memory comparison of non-target/target stimuli. P3 amplitude presented a more uniform scalp distribution in middle-aged and in elderly subjects and pnly decreased significantly with advancing age in men, which may explain the divergent results in the literature on aging-related changes of P3 amplitude.