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 (single 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 successive 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 spectral change relative to that under rest control. The main results were: (i) the power of delta and theta activity increased significantly in the 1st 0.5 s in all 4 conditions but decreased in the following epochs; (ii) the theta activity revealed greatest spatial differentiation, prominent 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 1st 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 frontal 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 further evidence indicating the functional correlates of EEG activities in each frequency band. The high frequency activity might reflect the general attention state. The dynamic change of attentional demand during information processing was probably reflected by alpha activity. The delta, theta and beta activities seemed related to different aspects of cognitive processes.