Medial prefrontal cortex generates frontal midline theta rhythm

Abstract

Frontal midline theta rhythm (Fm theta) is a distinct theta activity of EEG in the frontal midline area that appears during concentrated performance of mental tasks in normal subjects and reflects focused attentional processing. To tomographically visualize the source current density distributions of Fm theta, we recorded Fm theta by using a 64-channel whole-head MEG system from four healthy subjects, and applied a new analysis method, synthetic aperture magnetometry (SAM), an adaptive beam forming method. Fm theta was observed in the MEG signals over the bilateral frontal regions. SAM analysis showed bilateral medial prefrontal cortices, including anterior cingulate cortex, as the source of Fm theta. This result suggests that focused attention is mainly related to medial prefrontal cortex.

Frontal theta EEG activity correlates negatively with the default mode network in resting state

“…However, for a dipole that is placed either at the nearest suprathreshold voxel, or at the local maximum in the medial frontal cluster that explains the most variance, the dipole fit was qualitatively similar to the unconstrained fit. Interestingly, Ishii et al (1999) used a beamformer approach on MEG data to estimate the location of the theta source, and located it in a region that largely overlaps with the medial frontal fMRI cluster observed in this experiment. If the cluster is the source location of the frontal theta activity, the substantial size of this cluster suggests a distributed source for frontal theta.…”

“…The first line of evidence is that it has been shown that the medial frontal cortex (our major cluster) is a likely source of frontal theta activity. Source modeling attempts have located the source of frontal theta effects in medial frontal areas Gevins et al, 1997;Ishii et al, 1999;Onton et al, 2005). However, most of these attempts used equivalent dipole models and located the frontal theta in or near the anterior cingulate region, somewhat posterior and deeper than the observed medial frontal theta-BOLD cluster Gevins et al, 1997;Onton et al, 2005).…”

“…A speculative hypothesis then is that the DMN operates in theta mode (which is reflected in the scalp EEG by an increase in frontal theta) when it becomes less active (i.e., during engagement in a task). This would not only explain the observed BOLD decreases during engagement in a task Raichle et al, 2001), but it would also explain why frontal theta power has been shown to increase in a wide range of cognitive tasks, such as mental arithmetic Burgess and Gruzelier, 1997;Inanaga, 1998;Inouye et al, 1994;Iramina et al, 1996;Ishihara and Yoshii, 1972;Ishii et al, 1999;Lazarev, 1998;Mizuki et al, 1980;Sasaki et al, 1996;Smith et al, 1999), error detection tasks (Luu et al, 2003;Luu et al, 2004), language comprehension tasks (Bastiaansen et al, 2002;Hald et al, 2006) and working memory tasks (Gevins et al, 1997;Jensen and Tesche, 2002;Krause et al, 2000;Onton et al, 2005). However, although this suggestion would account for the observed pattern of theta power increases, it appears to contradict several previous functional interpretations that increased frontal theta oscillations reflect synchronous activity in brain regions that are involved in cognitively demanding tasks (Inanaga, 1998;Ishihara and Yoshii, 1972;Jensen and Tesche, 2002;Laukka et al, 1995;Onton et al, 2005;Smith et al, 1999).…”

“…This component has a frequency range of roughly 3-8 Hz, and is most prominent over midline fronto-central electrodes. Frontal theta has been observed during various cognitive activities that require attention or short term memory (Burgess and Gruzelier, 1997;Inanaga, 1998;Ishihara and Yoshii, 1972;Laukka et al, 1995;Lazarev, 1998;Smith et al, 1999), and is often studied during mental arithmetic Burgess and Gruzelier, 1997;Inanaga, 1998;Inouye et al, 1994;Iramina et al, 1996;Ishihara and Yoshii, 1972;Ishii et al, 1999;Lazarev, 1998;Mizuki et al, 1980;Sasaki et al, 1996;Smith et al, 1999). More recently, frontal theta power has been found to increase with working memory load (Gevins et al, 1997;Jensen and Tesche, 2002;Krause et al, 2000;Onton et al, 2005), indicating a possible role of theta oscillations in working memory maintenance.…”

“…More recently, frontal theta power has been found to increase with working memory load (Gevins et al, 1997;Jensen and Tesche, 2002;Krause et al, 2000;Onton et al, 2005), indicating a possible role of theta oscillations in working memory maintenance. Source modeling attempts have localized the frontal theta rhythm to the anterior cingulate or the medial frontal cortex Gevins et al, 1997;Ishii et al, 1999;Onton et al, 2005). Interestingly, Mizuhara et al (2004) as well as Sammer et al (2005Sammer et al ( , 2007 demonstrated that frontal theta increases can be observed in the EEG acquired during fMRI.…”