Frontal midline theta rhythms reflect alternative activation of prefrontalcortex and anterior cingulate cortex in humans

Frontal midline theta rhythm (Fm theta) often appears on electroencephalogr am (EEG) during consecutive mental tasks. To clarify the source of rhythmic activity, magnetoencephalogram (MEG) and EEG were simultaneously measured in six healthy volunteers during different mental tasks using whole head ME G system. MEG records were averaged every one cycle of Fm theta rhythms usi ng individual positive peaks of Fm theta waves in Fz EEG as a trigger. Aver aged theta components of MEG signa Is were analyzed with a multi-dipole mod el. Two sources were estimated to the regio ns both of the prefrontal-media l superficial cortex and anterior cingulate cortex (ACC). These regions wer e alternatively activated in about 40 to 120 degrees phase shift during one Fm theta cycle. From above results, we hypothesize that appearance of Fm t heta during consecutive mental tasks reflects alternative activities of the medial prefrontal cortex and ACC. (C) 1999 Published by Elsevier Science I reland Ltd. All rights reserved.