Contentless thinking is associated with overall positive inter-areal connectivity configurations

During spontaneous mentation, our minds are occupied with different contents, including periods of contentless thinking (mind blanking). As the frequency of mind blanking events is non-negligible, an emerging question is whether this mental state constitutes an accidental blip or rather a default function of our ongoing mental flow. Using fMRI experience-sampling in 36 typical subjects during which mind blanking could be chosen among various mental states, we show that mind blanking (MB) is less frequent (6%) compared to sensory-oriented (Sens, 19%), stimulus-dependent (SDep, 31%), and stimulus-independent thoughts (SInd, 43%), distributed equally across time (Chi-square uniformity test, χ2(9)=6.18, p=0.72). The probability of reporting mind blanking is low but equal when departing from the other states (Markov chain transition probability=0.06), suggesting that this state is not driven by specific mental content; also, the low probability (0.04) to re-enter mind-blanking indicates that contentless reports may be less anchoring as compared to content-oriented thinking. FMRI phase-based coherence showed that a recurrent brain pattern of overall positive functional connectivity was closer to mind blanking reports (in the sense of Euclidean distance) compared to other mental states (p=0.035 for MB vs. Sens and p<0.001 for MB vs. SDep and MB vs. SInd, linear mixed effect model and posthoc Tukey's test). This indicates that mind blanking is a default mental state supported by an over-connected brain configuration. Such overall positive connectivity can reflect a distributed fight of multiple local units to enter into the supervisory attentional system, which may hinder reportable mental content formation.