Directing attention toward the body's internal signals (interoception) versus external sounds (exteroception) produces distinct brain activity patterns. Exteroceptive attention flattened overall brain wave power, while interoceptive attention reduced brain signal complexity, increased frontal connectivity and theta oscillations, and modulated the heartbeat-evoked potential (HEP). Classifiers using HEP features correctly identified the attentional state in 17 of 20 healthy participants; power spectral density features classified all 20. In five brain-injured patients, one with unresponsive wakefulness syndrome and one with locked-in syndrome showed willful modulation of the HEP, suggesting they could follow commands. These findings highlight how attention shapes sensory processing and may aid diagnosis in disorders of consciousness.
Pupil size is influenced not only by light but also by mental factors like perceived brightness. In healthy people, seeing images that semantically imply brightness (e.g., the sun) causes greater pupil constriction than looking at control images of similar luminance. This study tested whether this effect could detect residual cognition in non-communicating patients with disorders of consciousness. In ten healthy participants and seventeen patients (ten minimally conscious, six in vegetative state/unresponsive wakefulness syndrome, one emerging from minimally conscious state), pupillary responses were measured while viewing photographs of the sun versus matched-luminance controls (moon photos, scrambled sun images, gray squares).