Evoked brain rhythms are altered markedly in middle-aged subjects: single-sweep analysis

In this study, a new method for analysis of single frequency responses was applied to compare auditory evoked potentials between young (18-30 years old) and middle-aged (50-55 years old) adults. The method was related to the evoked brain rhythmicities concept and permitted to quantify separately the magnitude, phase-locking, and enhancement against prestimulus activity of single sweeps. Thus, a constellation of three single-sweep parameters was used. No differences could be detected between the two age groups in the conventionally averaged potentials. However, significant age-related alterations were found at the level of single sweep analysis: 1) At the three midline locations (Fz, Cz, and Pz) older adults manifested theta phase-locking and enhancement that were significantly stronger than those in young adults; 2) In contrast, the alpha responses only over the frontal brain area were stronger in phase-locking and enhancement in middle-aged than in young adults, which implies that the alpha response system may be specifically related to frontal brain functioning during aging.