The dynamics of EEG microstates covary with spontaneous thoughts

Brain activity continuously fluctuates alongside the spontaneously co-occurring mental events that comprise our spontaneous thought. Understanding the functional relevance of this intrinsic activity requires investigation of the covariation between ongoing brain dynamics and spontaneous thought. The large-scale electrophysiological events known as electroencephalographic (EEG) microstates provide an important window into the activity of neuronal networks at the millisecond time scale, and sequences of microstates are thought to reflect cognitively relevant mental operations. Yet, attempts to link momentary thoughts to the dynamics of microstates through more temporally precise experience sampling methods have been limited. We address this gap by asking participants to report on the content and quality of their spontaneous thought across nine experiential dimensions by answering questions adapted from the Amsterdam Resting-State Questionnaire (ARSQ) after eight separate EEG recording periods where participants engaged in eyes-closed rest. We found that individuals' retrospective reports of the flow of their thought content varied substantially from one moment to the next and were coupled with the dynamics of microstates. In particular, microstates C and E demonstrate associations with several prominent features of spontaneous thought, providing links between these electrophysiological events and large-scale functional brain networks thought to be involved in internal cognition and self-generated mental processes. Together, these findings elucidate the functional relevance of microstates by linking their dynamics to distinct dimensions of spontaneous thought and demonstrate the utility of more temporally precise experience sampling approaches to capture thoughts in individuals at rest.