When people are not engaged in an explicit task, they experience a variety of self-generated thoughts, such as planning or reminiscing. Using machine learning to analyze brain activity from resting-state fMRI scans, researchers identified distinct neural states that recur over time. Two of these states predicted different patterns of thinking. One neural state, resembling activity seen during demanding tasks, was linked to problem-solving about the future. Another state, associated with less demanding conditions, was tied to intrusive thoughts about the past. These two states fell at opposite ends of a brain hierarchy related to cognitive demand. The findings show that tracking moment-to-moment changes in brain function can help classify self-generated mental states and that these states align with the brain's response to cognitive tasks.
Inhalation of DMT, a serotonergic psychedelic, produces a brief surge in sympathetic nervous system activity—heart rate, skin conductance, and respiration—that closely tracks the intensity of the emotional experience. Nineteen participants received 20 or 40 mg of DMT under a semi-naturalistic blinded design. Higher doses caused heart rate and breathing to increase within the first two minutes, while skin conductance rose only later, indicating a prolonged autonomic response. As the drug's effects waned, feelings of pleasantness and bliss emerged. Combining simple physiological measures with moment-by-moment self-reports offers a way to objectively characterize psychedelic-induced emotional states, which may aid future clinical biomarker research.