THE TEMPORAL AND SPATIAL FEATURES OF EVENT-RELATED EEG SPECTRAL CHANGES IN 4 MENTAL CONDITIONS

Event-related EEG spectral perturbation (ERSP) was studied in 20 right -handed subjects during selective response (SRP) and selective mental arithmetic (SMA). The input signals were one-digit number sounds (sing le syllable). The subjects were asked to make switch response (for SRP ) or accumulative summation (for SMA) as soon as odd numbers (T) were heard and to ignore even ones (N). EEG powers were derived from 3 succ essive 0.5 s segments post input signal from 9 locations on scalp in 4 conditions (srT, srN, maT and maN). The ERSP was taken as the spectra l change relative to that under rest control. The main results were: ( i) the power of delta and theta activity increased significantly in th e 1st 0.5 s in all 4 conditions but decreased in the following epochs; (ii) the theta activity revealed greatest spatial differentiation, pr ominent theta activity remained at Fz in the 2nd and 3rd 0.5 s in maT but not in srT; (iii) the power of alpha activity was lowest in the 1s t 0.5 s and remained low level during SMA but increased in the 2nd 0.5 s during SRP; (iv) the 11-18 Hz activity augmented after the 1st 0.5 s, its dominance remained at P6 during SMA but: switched from P6 to fr ontal locations during SRP; (v) the power of high frequency activities beyond 30 Hz decreased significantly during SRP at all locations. The temporal and spatial feature of ERSP in the 4 conditions provided fur ther evidence indicating the functional correlates of EEG activities i n each frequency band. The high frequency activity might reflect the g eneral attention state. The dynamic change of attentional demand durin g information processing was probably reflected by alpha activity. The delta, theta and beta activities seemed related to different aspects of cognitive processes. (C) 1998 Elsevier Science Ireland Ltd.