Probability mapping: power and coherence analyses of cognitive processes.

In recent years different mapping techniques have proved to be an efficient means in studying cognitive processes. Our approach is based on recordings with 19 EEG channels and the computation of spectral parameters. Power and coherence values are obtained from the EEG of control recordings and recordings during the performance of cognitive tasks and are compared for significant differences. The statistical procedures used yield descriptive error probabilities for the rejection of the null hypothesis which are mapped either colour coded or by black and white squares. The usefulness of this method is demonstrated on a mental cube rotation study involving 31 students, 13 males and 18 females. One essential result during the performance of this test is an increase of theta power only in females. As far as local coherence and the theta band are concerned, males show increased values right parietally and right temporo-occipitally; opposed to this, in females the left hemisphere is more affected. In the beta bands, local coherence increases in males right parietally and left temporo-occipitally. Contrary to this, in females the parietal increase of local coherence is more accentuated in the left hemisphere but temporo- occipital coherence is increased in the right hemisphere. In both sexes interhemispheric parietal coherence increases during cube rotation suggesting increased functional couplings between the hemispheres. This study demonstrates that the inclusion of the coherence parameter in brain mapping furthers the detection of sex and hemispheric differences during the performance of cognitive tasks.