Constructing thought spontaneously and deliberately: neural bases and adaptive strategies

Human thought spans a continuum from spontaneous to deliberate forms. Spontaneous thought occurs when attention shifts from ongoing activities to task-unrelated content (mind-wandering), whereas deliberate thought involves voluntarily imagining future events (mental time travel; MTT) or setting goals (prospective memory; PM). Both forms of thought engage multiple brain networks – notably, the Default Mode Network (DMN) with key hubs in the ventromedial prefrontal cortex (vmPFC) and hippocampus – while external attention is primarily mediated by the Dorsal and Ventral Attention Networks. However, there is still no consensus on the neural and cognitive mechanisms underlying spontaneous and deliberate thought, their relationship with external attention, and optimal strategies for promoting adaptive thinking. Chapter 1 explores the neural bases of mind-wandering and external attention, adopting a tDCS protocol that assesses both simultaneously. Findings reveal that the posterior parietal cortex mediates both internal and external attention, while the vmPFC uniquely supports future-oriented mind-wandering. Chapter 2 examines whether activating mental representations (self-schema and the future time) promotes adaptive mind-wandering. Results show that activating representations of future time increases aware mind-wandering, whereas activating self-schema promotes unaware mind-wandering. Chapter 3 investigates the role of the vmPFC in deliberate thought (MTT), examining the temporal unfolding of memory structures (“think aloud” method) during event construction. Patients with vmPFC damage show degraded personal semantic information and atypical, “backward” transitions from lower- to higher-level memory structures, reporting fewer specific events. Finally, Chapter 4 explores the simultaneous effect of intention offloading (use of external reminders) on both spontaneous (mind-wandering) and deliberate (PM) thought. Results indicate that offloading reduces pupil diameter, especially under high memory load, and decreases off-task thinking over time. Collectively, this work clarifies the cognitive, neural, and physiological mechanisms underlying internal (spontaneous and deliberate thought) and external attention, identifying strategies to foster adaptive thinking.