Alterations of continuous MEG measures during mental activities

In a pilot study, we investigated the topography of 11 continuous MEG measu res for the eyes-opened and eyes-closed condition together with three simpl e mental tasks (mental arithmetic, visual imagery, word generation). One-mi nute recordings for each condition from 16 right-handed subjects were analy zed. The electrophysiological measures consisted of 6 spectral band measure s together with spectral edge frequency and spectral entropy, plus the time -domain-based entropy of amplitudes (ENA) and the nonlinear measures correl ation dimension D2 and Lyapunov exponent L1. In summary, our results indica te a pronounced task-dependent difference between the anterior and the post erior region, but no lateralization effects. Although the nonlinear measure s ranged in the middle field with respect to the number of significant cont rasts, they were the only ones to be partially successful in discriminating the mental tasks from each other. The most efficient measure turned out to be the ENA. Under mental activation the ENA was larger than in both no tas k conditions (eyes opened and eyes closed). This finding reflects lower var iations of the maximum amplitude during performance of mental tasks than du ring no task states. Copyright (C) 2000 S. Karger AG, Basel.