IS THE ALPHA-RHYTHM A CONTROL PARAMETER FOR BRAIN RESPONSES

The main goal of the present study is to develop a conceptual analysis of alpha response in the brain based on single sweep evaluation. A ne w method was employed to estimate a set of single-sweep parameters and quantify the oscillatory behaviour of single, electroencephalograph ( EEG) sweeps. It was aimed to demonstrate that brain alpha responses ar e governed by spontaneous alpha activity and to validate the principle of brain response excitability. Because the spontaneous alpha activit y depends on both the topology of recording and the subject's age, top ology and age models were used. Spontaneous and evoked alpha activity were recorded at frontal and occipital sites in three groups of subjec ts: 3-year-old children, young adults and middle-aged subjects. Amplit ude, enhancement and phase-locking of single alpha responses to visual stimuli were analysed. Major results showed that: (1) visual alpha re sponses could be recorded only if the alpha rhythm was developed in th e spontaneous EEG independent of electrode location; (2) middle-aged a dults showed more expressed frontal spontaneous alpha activity in comp arison with young adults; (3) accordingly, alpha responses with higher amplitude and stronger phase-locking were produced over the frontal b rain area in middle-aged than young adults. These results validate the principle of brain response excitability and demonstrate that a shift towards frontal brain areas for both the spontaneous and evoked alpha activity occurs with increasing age in adults. The results are discus sed in the context of the diffuse and distributed alpha system of the brain. Age-dependent changes in frontal alpha activity are suggested t o be related to frontal brain functioning during aging.