Peak Alpha Frequency of EEG during a Mental Task: Task Difficulty and Hemispheric Differences

ABSTRACT To investigate the effect of task difficulty on the alpha wave, bilateral EEGs were recorded from frontal and occipital locations from 5 male and 5 female students while they were engaged in two arithmetic (simple addition, SA, and complex addition, CA) and two visuo‐spatial (visual imagery, VI, and mental rotation, MR) tasks. During both the arithmetic and the visuo‐spatial tasks, peak alpha frequency of power spectrum increased significantly above the resting level. Moreover, the frequency shift was significantly larger in the CA and MR conditions than in the SA and VI conditions. The shift increased as the task difficulty increased. A hemispheric effect was found: the peak alpha frequency increased in the left rather than in the right during the arithmetic tasks whereas it increased in the right rather than in the left during the visuo‐spatial tasks.