SEGREGATION OF THE THALAMIC ALPHA-RHYTHM FROM CORTICAL ALPHA-ACTIVITYUSING THE SAVIT-GREEN S-STATISTIC AND ESTIMATED CORRELATION DIMENSION

The large-amplitude, occipital alpha rhythm of the human electroenceph alogram (EEG) is associated in normal subjects with a state of relaxed wakefulness. We analyzed resting eyes-open and eyes-closed human EEG data using three measures: power in the 8-12-Hz alpha frequency band, estimated correlation dimension (D-2), and the Savit-Green S-statistic . At occipital loci, two groups of points were evident in the scatterp lot of S vs. estimated D-2. Group A was of higher dimension and consis ted of predominantly eyes-open records. Group B was of lower dimension and consisted of more eyes-closed than eyes-open records. Furthermore , Group B had a broad range of alpha power, with alpha power being neg atively correlated with estimated D-2 (higher alpha power associated w ith lower dynamical complexity). In contrast, Group A had a very small range of low alpha power, and was positively correlated with estimate d D-2 (higher alpha power associated with increased dynamical complexi ty). Our results indicate that Group B EEG (the alpha rhythm) and Grou p A EEG (EEG containing 'other' alpha activity) have fundamentally dif ferent dynamical properties. (C) 1997 Elsevier Science B.V.