Cognitive control and semantic thought variability across sleep and wakefulness

The flow of thought is persistent, and at times merciless. Mental content is generated throughout the day and into the night, moving forward predictably at times but surprisingly at others. Understanding what influences the trajectory of thought – how thoughts continuously unfold over time – has important implications for the diagnosis and treatment of spontaneous thought disorders like schizophrenia and recurrent nightmares. Here, we examine whether cognitive control (i.e., deliberate constraints) restrict moment-to-moment topical content shifts across sleep and wakefulness, thus acting as a fundamental constraint on thought variability. Thought variability was measured as the semantic distance between sequential thought phrases and was applied to reports from a variety of dreaming and waking experiences. Our results show that within both waking thought and dreams, conditions typically marked by higher levels of cognitive control are associated with decreased thought variability. During wakefulness, on-task conditions were associated with reduced levels of semantic thought variability compared to off-task conditions and semantic thought variability was greater when thoughts wandered around more freely. During sleep, lucid dreams marked by higher levels of metacognition were associated with reduced levels of semantic thought variability compared to non-lucid dreams. These results suggest that cognitive control may limit thought variability across the 24-hour cycle of thought generation. Such results are notably consistent with the Dynamic Framework of Thought, where mental states are expected to vary on continuum of deliberate constraints, with lower cognitive control leading to a categorical cluster of spontaneous thought processes that includes both mind-wandering during wakefulness and non-lucid dreams during sleep.