Individual differences in lateralisation of hallucinations associated with sleep paralysis.

Individual differences were investigated in the lateralisation of two general categories of hypnagogic and hypnopompic hallucinations associated with sleep paralysis: (1) Vestibular-motor (V-M) hallucinations; comprising sensations of floating, flying, illusory locomotion and postural adjustments, out-of-body experiences (OBE), and autoscopy; and (2) Intruder hallucinations; incorporating a sense of the presence, and visual and auditory hallucinations of external, alien agents. Left-right lateralisation of such hallucinations, as well as handedness and footedness, were assessed in a diverse, nonclinical sample of 201 subjects participating in a web-based survey of sleep paralysis experiences. V-M hallucinations, but not Intruder hallucinations were predicted, based on the hypothesised distinctive neural sources of the different hallucinations, to be positively associated with handedness and footedness. Specifically, the predictions were based on the hypothesis that the activation of components of a vestibular, motor, and kinaesthetic bodily-self neuromatrix underlies V-M hallucinations, whereas a threat-activated vigilance system is responsible for Intruder hallucinations. As predicted, limb preferences were consistently found to be significantly and positively associated with a side bias of V-M, but not Intruder, hallucinations.