Studying the default mode and its mindfulness-induced changes using EEG functional connectivity

doi:10.1093/scan/nst153 SCAN (2014) 9,1616 ^1624 Studying the default mode and its mindfulness-induced changes using EEG functional connectivity Aviva Berkovich-Ohana,1,2 Joseph Glicksohn,1,3 and Abraham Goldstein1,4 1 The Leslie and Susan Gonda (Goldschmied) Multidisciplinary Brain Research Center, Bar-Ilan University, Ramat Gan 52900, 2Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, 3Department of Criminology, and 4Department of Psychology, Bar-Ilan University, Ramat Gan 52900 Israel. Keywords: default mode network; mindfulness meditation; functional connectivity; mean phase coherence; electroencephalography INTRODUCTION This article focuses on two inter-related topics. The first is the identification of the electroencephalographic functional connectivity (EEGFC) signature of the default mode network (DMN). The DMN, mostly studied by functional magnetic resonance imaging (fMRI), is a taskinhibited network active during resting state and largely related with mind-wandering (Gusnard et al., 2001; Raichle et al., 2001; Buckner et al., 2008;) and self-referential activity (Northoff et al., 2006), which includes the medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), inferior parietal lobule (IPL), medial temporal lobe (MTL) and lateral temporal cortex (LTC) (Buckner et al., 2008). The second topic of this report is the study of EEG-FC alterations following mindfulness meditation (MM) practice and their possible relation with the DMN. MM, as practiced in the West and as studied in research paradigms, is a technique of remaining aware and noticing the salient features of present experience while refraining from evaluative processes, conceptual elaboration and mind wandering (Kabat-Zinn, 2003). Previous research has indicated that MM may engage mechanism for vigilance, monitoring and cognitive control (Lutz et al., 2008; Zeidan et al., 2010; Hölzel et al., 2011b). Thus, it was expected and indeed found that it would result in decreases of activity in areas of DMN, specifically in mPFC, which has been linked to self-referential narrative thinking and valuation. In this report we build on a recent publication on DMN activation during MM, in which we reported two major findings (BerkovichOhana et al., 2012). The first was the identification of DMN activity as a reduction in gamma power within frontal-midline regions during a time-production (TP) task compared with resting state. The choice Received 23 November 2012; Revised 29 August 2013; Accepted 23 September 2013 Advance Access publication 4 November 2013 This article is based on a dissertation written by the first author, A. B.-O., and submitted to Bar-Ilan University in partial fulfillment of the requirements toward the PhD degree. We thank Dr Zoran Josipovic and Dr Yi-Yuan Tang for suggesting very helpful comments to the previous version of this manuscript. The research was supported by the Mind and Life Institute Francisco J. Varela Research Award 6546 and a grant from the Bial Foundation (27/10). Correspondence should be addressed to Aviva Berkovich-Ohana, Department of Neurobiology, Weizmann Institute of Science, Rehovot 76100, Israel . E-mail: of the TP task to index a reduction in DMN activity was based on previous work showing that timing systematically activates several cortical regions, including: (i) attentional regions, such as the right parietal and dorsolateral prefrontal cortex (DLPFC) (reviewed by Walsh, 2003; Oliveri et al., 2009; Wittmann, 2009), consistent with a great body of behavioral studies showing that attention is mandatory for accurate timing (reviewed by Brown, 1997); (ii) the supplementary motor area (SMA) (Coull and Nobre, 1998; Ferrandez et al., 2003; Coull, 2004; Macar et al., 2004) and (iii) the anterior insular cortex (Craig, 2002, 2009; Wittmann et al., 2010). The right parietal and SMA regions are part of the dorsal attention network (Corbetta et al., 2008), comprising a task-activated network, also named the ‘extrinsic system’, suggested to be antagonistic to the task-inactivated DMN (Fox et al., 2005; Golland et al., 2007; Tian et al., 2007) and the DLPFC and anterior insular cortex are part of the frontoparietal control system, interposed between the ‘intrinsic’ and ‘extrinsic’ systems (Vincent et al., 2008) and possibly adjudicating between these two potentially competing brain systems (Vincent et al., 2008; Spreng et al., 2010; Smallwood et al., 2012). To conclude, the TP task is related with the task-activated network and the frontoparietal control system, hence with DMN deactivation. The second finding was that MM practitioners exhibited reduced frontal gamma power, related to DMN activity, as a trait (long term) effect. Nolfe (2011) called attention to the need to expand this study to include functional connectivity, which is precisely the aim of this work. There is a growing effort to establish the relationship between the DMN-related blood oxygenated level dependent (BOLD) fMRI signal and electrophysiology (Broyd et al., 2009). Most DMN-EEG studies investigated either spectral power (Chen et al., 2008; Berkovich-Ohana et al., 2012) or its correlation with the fMRI BOLD signal (Laufs et al., 2003; Mantini et al., 2007; Meltzer et al., 2007; Scheeringa et al., 2008). Accumulating evidence suggests that while DMN activity is generally negatively correlated with frontal and midline theta (4–8 Hz) power (Meltzer et al., 2007; Scheeringa et al., 2008), the activity in the prefrontal area of the DMN, which is strongly related to self-reference, is manifested in the gamma (25–45 Hz) power band (Mantini et al., 2007; Chen et al., 2008; Berkovich-Ohana et al., 2012). Additionally, the ß The Author (2013). Published by Oxford University Press. For Permissions, please email: The default mode network (DMN) has been largely studied by imaging, but not yet by neurodynamics, using electroencephalography (EEG) functional connectivity (FC). mindfulness meditation (MM), a receptive, non-elaborative training is theorized to lower DMN activity. We explored: (i) the usefulness of EEG-FC for investigating the DMN and (ii) the MM-induced EEG-FC effects. To this end, three MM groups were compared with controls, employing EEGFC (–MPC, mean phase coherence). Our results show that: (i) DMN activity was identified as reduced overall inter-hemispheric gamma MPC during the transition from resting state to a time production task and (ii) MM-induced a state increase in alpha MPC as well as a trait decrease in EEG-FC. The MMinduced EEG-FC decrease was irrespective of expertise or band. Specifically, there was a relative reduction in right theta MPC, and left alpha and gamma MPC. The left gamma MPC was negatively correlated with MM expertise, possibly related to lower internal verbalization. The trait lower gamma MPC supports the notion of MM-induced reduction in DMN activity, related with self-reference and mind-wandering. This report emphasizes the possibi (...truncated)