Heartbeat-evoked responses (HERs) in resting-state EEG can distinguish between postcomatose patients who are unresponsive and those in a minimally conscious state with 87% accuracy, 96% sensitivity, and 50% specificity. HERs provide more accurate classification than random EEG segments not locked to heartbeats or heart rate variability. HER-based consciousness scores correlate with glucose metabolism in the right superior temporal sulcus and right ventral occipitotemporal cortex. HERs reflect consciousness diagnosis based on brain metabolism better than behavior-based diagnosis (77% validation accuracy). These findings suggest HERs capture a capacity for consciousness that does not necessarily translate into intentional overt behavior.
Autonomic signals can reveal aspects of subjective and neural states. A Bayesian framework estimated heart rate entropy under psychedelics. Across four drugs—LSD, DMT, psilocybin, and ketamine—mean heart rate, high-frequency heart rate variability, and heart rate entropy consistently increased during the psychedelic experience. These changes predicted various dimensions of the experience. Heart rate entropy increases correlated with brain entropy increases, while other autonomic markers did not. Cost-efficient autonomic measures can reveal detail about subjective and brain states, opening new research avenues in neuroscience.