Phantom Boarder and Presence Hallucinations: overlapping mechanisms?

© 2023 EPFL

© 2023 EPFL

Novel work relating Phantom Boarder Syndrome and Presence Hallucinations published in Movement Disorders Clinical Practice

Olaf Blanke, Fosco Bernasconi and Jevita Potheegadoo’s study into the phenomenon of Phantom Boarders (PB) investigated the underlying mechanisms of this unsolved symptom, commonly occurring in various form of neurodegeneration, including dementia with Lewy Bodies (DLB), Parkinson’s disease (PD), Alzheimer’s disease (AD) and vascular dementia (Nagahama et al., 2007; Aarsland et al., 2001; Hwang et al., 2003).

The Phantom Boarder Syndrome – the eery and often unsettling feeling that someone you cannot see or hear, is present in your house while no one is there (Rowan, 1984) - has had a patchy history of clinical exploration (Kasahara et al., 2005) and to date no scientific study has been carried out. It is often accompanied by the sensation that this unwelcome intruder is malevolent, there to rob or harm or has even moved into the person’s house, and so can be highly disruptive to patients and their caregivers. Adding to its clinical relevance, it is also a predictor for early home placement and delirium (Gottesman & Stern, 2019).

Due to its co-occurrence with such persecutory thoughts, it has been classified as either a delusional misidentification syndrome (Burns et al., 1990) or a complex hallucination, when the presence can also be seen or heard (Ballard et al., 1995), but its exact specification remains unclear (Blanke et al., 2023). In analogy with presence hallucinations (PH; feeling of someone you cannot see or hear, present close to your body (Fénelon et al., 2011), the intruder in PB is felt as a presence but is experienced farther away and at variable places within the living environment of the affected patient. Given these similarities, our team has investigated the shared brain mechanisms between PB and PH.

In this clinical-experimental study, the sensitivity to robot-induced presence hallucinations was experimentally tested (Bernasconi, Blondiaux et al., 2021) in a sample of rare PD patients with PB (and PH), in PD patients with PH-only and in PD patients without PB or PH. The team found that the sensitivity to robot-induced PH of PD-PB patients closely mirrored that of the PD-PH-only patients. Both groups reported higher levels of such PH than PD patients who didn’t exhibit either PB or PH symptoms in daily life. Further work is needed and planned to validate these findings in a cohort of PD patients with exclusively PB syndrome, also including neuropsychological and fMRI data. The present study represents the first line of evidence indicating that despite their phenomenological divergence, PH and PB could both potentially stem from altered sensorimotor processing involving altered self-processing mediated by fronto-temporal regions (Bernasconi, Blondiaux, et al., 2021; Blanke et al., 2014).


This project was supported by two generous donors advised by CARIGEST SA, the first one wishing to remain anonymous and second one being Fondazione Teofilo Rossi di Montelera e di Premuda; the Bertarelli Foundation; the Swiss National Science Foundation (grant number FNS 320030_188798).


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