Age effects on visual EEG responses reveal distinct frontal alpha networks Vasil Kolev a, * , Juliana Yordanova a , Canan Basar-Eroglu b , Erol Basar c,d a Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 23, 1113, Sofia, Bulgaria b Institute of Psychology and Cognition Research, University of Bremen, Bremen, Germany c School of Medicine, Dokuz Eylu ¨l University, Izmir, Turkey d TU ¨ BITAK Brain Dynamics Research Unit, Ankara, Turkey Accepted 21 March 2002 Abstract 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. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Visual evoked potentials; Single-sweep analysis; Alpha response; Phase-locking; Aging; Frontal alpha rhythm 1. Introduction Electroencephalographic activity (EEG) recorded at the scalp can provide important information about changes in neuroelectric organization taking place in the course of life span. In most studies, the spontaneous EEG is analyzed, both qualitatively and quantitatively (reviewed in Nieder- meyer, 1997). It has been shown that aging produces speci- fic changes in the frequency content of the spontaneous EEG. More specifically, an increase in slow (delta, 0–4 Hz and theta, 4–7 Hz), and fast (above 15 Hz) frequency EEG activities has been described (Niedermeyer, 1997; Polich, 1997). Most substantial age-dependent variations have been reported for the alpha frequency band (7–14 Hz). Three major patterns of alterations are outlined (Fisch, 1991; Niedermeyer, 1997): (1) a general decrease of spectral alpha power, with this effect being most pronounced at occipital locations; (2) alpha slowing produced by a reduc- tion of dominant alpha frequency; (3) a shift in the distribu- tion of spectral alpha power and alpha incidence from posterior to anterior locations. Most recent findings addi- tionally indicate that the interhemispheric functional connectivity under resting conditions decreases with age as reflected by low coherence in all frequency bands includ- ing alpha (Kikuchi et al., 2000). The effects of processing demands on alpha activity have also been analyzed as a function of age. Functional alpha reactivity is reported to decrease with aging, which has been established for visual performance (Kononen and Partanen, 1993; Marciani et al., 1994; d’Onofrio et al., 1996), odor detection and identification (Kemp et al., 2001), and mental arithmetic (Marciani et al., 1994). However, in elderly adults, a greater activation of both the slow and fast alpha bands at anterior sensorimotor regions has been found during a simple motor task (Sailer et al., 2000), and a higher interhemispheric connectivity in the alpha range has emerged during photic stimulation (Kikuchi et al., 2000). Furthermore, in a spatial working memory task, an addi- tional reactivity of frontal alpha EEG has been detected in old as compared to young adults (McEvoy et al., 2001). Taken together, these previous results imply that the Clinical Neurophysiology 113 (2002) 901–910 1388-2457/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S1388-2457(02)00106-2 www.elsevier.com/locate/clinph CLINPH 2001786 * Corresponding author. Tel./fax: 1359-2-979-37-49. E-mail address: kolev@iph.bio.bas.bg (V. Kolev).