ABSTRACT.Mu rhythms can be considered as intrinsic or resting activity of the central region. Somatosensory stimulations or motor behavioral activity affect the generation mechanism of mu rhythms and result in an amplitude attenuation or blocking reaction. Mu rhythms can be found only in a small part of the population when standard electrode montages and visual EEG evaluation are used. Mu rhythms can be detected in nearly 100% of cases when closely spaced electrodes in a transverse montage are used and the EEG is recorded during slowly repeated, voluntary movements. Mu rhythms are of great importance in functional testing of patients with cerebrovascular insufficiency.