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

Abstract

Frontal midline theta rhythm (Fmθ) often appears on electroencephalogram (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 MEG system. MEG records were averaged every one cycle of Fmθ rhythms using individual positive peaks of Fmθ waves in Fz EEG as a trigger. Averaged theta components of MEG signals were analyzed with a multi-dipole model. Two sources were estimated to the regions both of the prefrontal-medial superficial cortex and anterior cingulate cortex (ACC). These regions were alternatively activated in about 40 to 120° phase shift during one Fmθ cycle. From above results, we hypothesize that appearance of Fmθ during consecutive mental tasks reflects alternative activities of the medial prefrontal cortex and ACC.