Age effects on visual EEG responses reveal distinct frontal alpha networks

Objectives: The present study aimed to describe the effect of aging on single-trial visual alpha responses. Methods: Visual evoked potentials were recorded at F3, Cz, P3, and O1 in 12 young (20–30-year-olds) and in 10 middle-aged adults (50–55-year-olds). Slow (7–10 Hz) and fast (10–15 Hz) alpha frequency bands were analyzed. Three parameters of single alpha responses were assessed for the 0–300 ms period after stimulus: (i) maximal single-sweep amplitude; (ii) phase-locking with stimulus, and (iii) enhancement of post-stimulus relative to pre-stimulus alpha activity. Results: Ongoing alpha activity at anterior sites was larger in middle-aged subjects. Age differences in response amplitude depended on the anterior shift of ongoing alpha activity. Over fronto-central areas, the phase-locking of fast alpha responses was significantly increased, whereas the phase-locking of slow alpha responses was decreased in middle-aged compared to young adults, independently of amplitude. In contrast to slow alpha responses, frontal and occipital fast alpha responses were interrelated. Conclusions: These observations are in accordance with previous findings from the auditory modality implying that the age-related changes in frontal alpha oscillations are modality-independent. Slow and fast frontal alpha responses were affected differentially by the age, which might reflect the activations of functionally distinct alpha networks.