The Origins of a Spontaneous Thought: EEG Correlates and Thinkers’ Source Attributions

Spontaneous thoughts can arise from past memories, future tasks, and environmental cues. We developed a paradigm to investigate the stream of consciousness leading to spontaneous thoughts. While performing a concentration exercise (9 min) requiring one to focus only on one’s breathing, subjects observed spontaneous thoughts and counted the number of cognitions/percepts (‘links’) that they believed led to each spontaneous thought. In Studies 1–3, subjects reported less than 2 links per thought, over 80% of thoughts were attributed to a known cause, and roughly half of the thoughts were attributed to something outside the current environment. In Study 4, we examined the neural correlates of spontaneous thoughts triggered by external stimuli or internal, stimulus-independent factors (e.g., memories). Continuous EEG was recorded from seven active electrode sites (Fz, Cz, Pz, F3, F4, P3, and P4) as subjects indicated experiencing a thought. Subjects indicated whether their thoughts arose from internal (e.g., memories) or external (sights, sounds, smells, and bodily sensations) factors. To examine the neural correlates of each individually-reported thought, EEG was examined in short time scales (< 1 s) preceding each button press. Increased alpha correlation was observed for internal thoughts compared to a baseline condition (eyes-opened resting). In addition, increased alpha correlation in the parietal region was observed for internal compared to external thoughts. These findings are in line with previous research implicating distinct brain networks for internal and external awareness. We discuss the implications and potential future applications of this new approach for investigating the stream of consciousness.