Oscillatory brain dynamics, wavelet analysis, and cognition

On the basis of a systems theoretical approach it was hypothesized that eve nt-related potentials (ERPs) are superpositions of stimulus-evoked and time -locked EEG rhythms reflecting resonance properties of the brain (Basar, 19 80). This approach led to frequency analysis of ERPs as a way of analyzing evoked rhythms. The present article outlines the basic features of ERP freq uency analysis in comparison to ERP wavelet analysis, a recently introduced method of time-frequency analysis. Both methods were used in an investigat ion of the functional correlates of evoked rhythms where auditory and visua l ERPs were recorded from the cat brain. Intracranial electrodes were locat ed in the primary auditory cortex and in the primary visual cortex thus per mitting ''cross-modality'' experiments. Responses to adequate stimulation ( e.g., visual ERP recorded from the visual cortex) were characterized by hig h amplitude alpha (8-16 Hz) responses which were not observed for inadequat e stimulation. This result is interpreted as a hint at a special role of al pha responses in primary sensory processing. The results of frequency analy sis and of wavelet analysis were quite similar, with possible advantages of wavelet methods for single-trial analysis. The results of frequency analys is as performed earlier were thus confirmed by wavelet analysis. This suppo rts the view that ERP frequency components correspond to evoked rhythms wit h a distinct biological significance. (C) 1999 Academic Press.