The analyses of brain functions based on wavelet coherence of EEG gamma-band activities: An application to a perceptual grouping task

Abstract

The wavelet coherence analysis of induced EEG gamma-band activities was applied to investigate brain mechanisms of perceptual grouping. EEGs were measured from 63 scalp positions on the whole head during a perceptual grouping task. It was found that induced EEG gamma-band activities depended on the display position of a visual target presented in the task. The induced gamma-band activities were mainly observed at the frontal, parietal and occipital areas. Furthermore, it was found that the duration of induced EEG gamma-band activities reflected the difficulty of the task. The wavelet coherence between the frontal and parietal/occipital areas showed the significant decrease. The wavelet coherence at pre-stimulus periods was found to be dependent on the distance between two activated areas. In addition, the duration of the significant decrease of wavelet coherence increased corresponding with the difficulty of the task. Thus it was inferred that the decrease of wavelet coherence between two activated areas was caused by the finite transmission time of information from one area to the other. These results demonstrate that wavelet coherence could clearly detect short, significant episodes of synchronized cortical activities among multiple cortical areas associated with perceptual grouping.