title: Causal relationship between effective connectivity within the default mode network and mind-wandering regulation and facilitation.
abstract: Transcranial direct current stimulation (tDCS) can modulate mind wandering, which is a shift in the contents of thought away from an ongoing task and/or from events in the external environment to self-generated thoughts and feelings. Although modulation of the mind-wandering propensity is thought to be associated with neural alterations of the lateral prefrontal cortex (LPFC) and regions in the default mode network (DMN), the precise neural mechanisms remain unknown. Using functional magnetic resonance imaging (fMRI), we investigated the causal relationships among tDCS (one electrode placed over the right IPL, which is a core region of the DMN, and another placed over the left LPFC), stimulation-induced directed connection alterations within the DMN, and modulation of the mind-wandering propensity. At the behavioral level, anodal tDCS on the right IPL (with cathodal tDCS on the left LPFC) reduced mind wandering compared to the reversed stimulation. At the neural level, the anodal tDCS on the right IPL decreased the afferent connections of the posterior cingulate cortex (PCC) from the right IPL and the medial prefrontal cortex (mPFC). Furthermore, mediation analysis revealed that the changes in the connections from the right IPL and mPFC correlated with the facilitation and inhibition of mind wandering, respectively. These effects are the result of the heterogeneous function of effective connectivity: the connection from the right IPL to the PCC inhibits mind wandering, whereas the connection from the mPFC to the PCC facilitates mind wandering. The present study is the first to demonstrate the neural mechanisms underlying tDCS modulation of mind-wandering propensity.
authors.affiliation: Graduate School of Education, Kyoto University, Kyoto 606-8501, Japan; Japan Society for the Promotion of Science, Tokyo 102-8471, Japan. Electronic address: kajimura.shogo.25e@st.kyoto-u.ac.jp.
authors.forename: Shogo
authors.initials: S
authors.lastname: Kajimura
authors.affiliation: ATR Brain Information Communication Research Laboratory Group, Kyoto 619-0288, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Kochiyama
authors.affiliation: Kokoro Research Center, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Nakai
authors.affiliation: Kokoro Research Center, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Nobuhito
authors.initials: N
authors.lastname: Abe
authors.affiliation: Graduate School of Education, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Michio
authors.initials: M
authors.lastname: Nomura
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology*; D015984:Causality; D002540:Cerebral Cortex / Q000502:physiology*; D056344:Executive Function / Q000502:physiology*; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D013850:Thinking / Q000502:physiology*
keywords: Default mode network; Effective connectivity; Mind wandering; Spectral dynamic causal modeling; Transcranial direct current stimulation