Hallucinations in nonclinical populations are shaped by culture. Comparing Dutch and Qatari adults (2,999 each) on the Questionnaire for Psychotic Experiences, tactile and olfactory hallucinations occurred at similar lifetime rates in both countries. Auditory and visual hallucinations were twice as common in the Dutch sample, and Dutch participants reported younger ages of onset for auditory and tactile hallucinations. Although Qatari participants reported fewer auditory and visual hallucinations overall, those who experienced them had higher mean scores for past-week hallucinations, more impact on daily functioning, and more frequent commanding voices. The findings suggest hallucinations in the Qatari sample carried greater clinical relevance, with implications for early screening and prevention.
Sleep dysfunction and hallucinatory experiences are bidirectionally related, with the strongest path leading from poor sleep to hallucinations. This narrative review examines mechanisms across four levels: phenomenology, psychology, neural networks, and neurophysiology. Stress is a well-supported mediator, with sleep manipulation studies in non-clinical populations showing its role. Sleep loss also affects nervous system inflammation, altering brain connectivity involved in hallucinations. Lived-experience accounts reveal three novel mechanisms—source monitoring, mental resilience, and reasoning skills—that are impacted by sleep loss, though the full causal chain requires further testing. Priorities include testing stress as a mediator in clinical populations and experimentally examining these novel mediators.
Psychotic-like experiences (hallucinations or delusions below the threshold of a disorder) are common in the general population. In interviews with 12 female undergraduate students in Qatar, these experiences were prevalent. Students' descriptions showed that culture and religion shaped the types of hallucinations and some delusions they reported. Many students normalized their experiences and linked them to real-life events, possibly as a defense against the stigma of mental illness and being labeled abnormal.
People who experience auditory hallucinations while falling asleep (hypnagogic) or waking up (hypnopompic) show heightened brain sensitivity to sounds. In a behavioral study, 26 hallucinators reported greater subjective sensitivity to environmental sounds than 74 controls. Two fMRI experiments with 12 hallucinators and 12 matched controls found that hallucinators had greater speech-evoked brain activation in the left supramarginal gyrus. When directing attention to sound, they showed stronger activation in the anterior cingulate gyrus. These findings suggest that a tendency toward hallucinations involves increased auditory and polysensory cortex sensitivity, possibly due to enhanced attentional bias from the anterior cingulate gyrus, supporting the idea that top-down modulation of auditory cortex responses is key to generating auditory hallucinations.