Sleep paralysis and "the bedroom intruder": the role of the right superior parietal, phantom pain and body image projection.

Sleep paralysis involves temporary motor paralysis while awake, often accompanied by hallucinations of a menacing shadowy intruder in the bedroom. This paper proposes that such hallucinations arise from a functional disturbance in the right parietal cortex, specifically the temporoparietal junction, which processes body and self. The perceived intruder may be a hallucinated projection of the brain's internal body image (homunculus) from the right superior parietal lobule. The authors suggest testing this by studying individuals with conditions like apotemnophilia or anorexia nervosa, who may have irregularities in their internal body image, to see if their hallucinations mirror those irregularities. If confirmed, this neurological explanation could offer relief to those who experience sleep paralysis and counter supernatural cultural interpretations.

Study at a glance

Abstract

Sleep paralysis (SP) is a common condition occurring either at sleep onset or sleep offset. During SP the sleeper experiences gross motor paralysis while the sensory system is clear. Hypnogogic and hypnopompic hallucinations are common during SP and may involve seeing, hearing, and sensing the presence of menacing intruders in one's bedroom. This "intruder" is often perceived as a shadowy humanoid figure. Supernatural accounts of this hallucinated intruder are common across cultures. In this paper, we postulate that a functional disturbance of the right parietal cortex explains the shadowy nocturnal bedroom intruder hallucination during SP. This hallucination may arise due to a disturbance in the multisensory processing of body and self at the temporoparietal junction. We specifically propose that this perceived intruder is the result of a hallucinated projection of the genetically "hard-wired" body image (homunculus), in the right parietal region; namely, the same circuits that dictate aesthetic and sexual preference of body morphology. One way to test this hypothesis would be to study clinical populations who may have genetically acquired "irregularities" in their internal hard-wired body image in the right superior parietal lobule (SPL); for example, individuals with apotemnophilia or anorexia nervosa. If such individuals experience SP (e.g., induced in a sleep lab), and they hallucinate this shadowy figure, one would predict that they would see humanoid shadows and shapes with body irregularities, mirroring their own internal body image morphology. If correct, our hypothesis will offer a neurological explanation for this nocturnal bedroom intruder that has been a source of controversy, and striking and implausible cultural interpretations throughout history. Indeed, if our proposed hypothesis is tested and corroborated, dissemination of such findings would provide great relief to SP experiencers worldwide and could potentially be used in a therapeutic context.