Age effects on visual EEG responses reveal distinct frontal alpha networks

The present study aimed to describe the effect of aging on single-trial visual alpha responses.

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.

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.

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.