Gender dependent EEG-changes during a mental rotation task.

This study is based on 30 students, 15 females and 15 males. EEG was recorded with 19 electrodes according to the international 10/20 system against averaged signals picked up from both ear lobes. Averaged power spectra and cross-power spectra between all electrode-positions were computed. Data were reduced to five frequency bands (theta, alpha1, alpha2, beta1 and beta2) and finally mean amplitude and coherence were computed. EEG-recordings were made during a mental rotation task (Shepard-figures). The obtained spectral parameters were compared with the corresponding values of a baseline activity with eyes open at rest. The results of statistical evaluations (paired Wilcoxon tests, Wilcoxon tests of independent samples) were presented in error probability maps. In males, local coherence decreased between the posterior left electrodes in the theta-band. In females, a decrease of coherence between the posterior right electrodes were observed in this frequency-band. In contrast to females, males showed an increase of coherence between frontal, central and parietal electrode positions in both hemispheres in the alpha1-band. The increase of local coherence in the beta1-band over the right temporo-parietal sites in the male group was more pronounced than in the female group. Especially in females, interhemispheric coherence increased between the posterior electrodes in the theta-, beta1- and beta2-ranges. This study suggests the involvement of many brain areas during mental rotation. Females show a rather symmetrical allocation of coherence increase in theta, beta1 and beta2.