Background Minor hallucinations (MH) affect 30-60% of patients with Parkinson’s disease (PD), and are considered precursors to structured visual hallucinations and cognitive decline. While the link between structured visual hallucinations and dementia is well established, the neuropsychological correlates of MH in PD remain unclear, with most studies finding no significant cognitive differences between patients with MH and those without any hallucinations.

Objectives Presence hallucinations (PH) being among the most prevalent MH in PD, we used a technological approach to experimentally induce PH to investigate whether sensitivity to such robot-induced PH aids in detecting cognitive differences between patients with MH and without hallucinations.

Methods Twenty-five PD patients with MH (PD-MH) and 25 without hallucinations (PD-nH) underwent a comprehensive neuropsychological assessment and a robotic somatomotor procedure that is able to induce PH. The sensitivity to report robot-induced PH was analyzed in relation to the cognitive performance in neuropsychological tests.

Results PD-MH patients reported more robot-induced PH than PD-nH patients, supporting previous findings. While both groups showed comparable performance in the different cognitive domains, we found a significant association between increased sensitivity to the PH-induction and poorer performance in frontal subcortical functions (executive functions), in PD-MH patients.

Conclusions These findings demonstrate that sensitivity to robot-induced PH reveals a previously undetected link between MH and frontal subcortical cognitive deficits in PD, pointing to shared underlying mechanisms between executive dysfunction and somatomotor processing. This approach offers a novel and clinically valuable means of identifying early cognitive vulnerability that standard assessments may overlook.

OB is inventor on patent US 10,286,555 B2 (Title: Robot-controlled induction of the feeling of a presence) held by the Swiss Federal Institute (EPFL) that covers the robot-controlled induction of presence hallucinations. OB is inventor on patent US 10,349,899 B2 (Title: System and method for predicting hallucinations) held by the Swiss Federal Institute (EPFL) that covers a robotic system for the prediction of hallucinations for diagnostic and therapeutic purposes. OB is cofounder and shareholder of Metaphysiks Engineering SA. OB is member of the board and shareholder of Mindmaze SA. OB, JP and FB are inventors on patent number EP24706201.1 (Title: Numerosity estimation impairment measurement system) held by the Swiss Federal Institute (EPFL) that covers the implicit measure of presence hallucinations.

This study was funded by 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; Parkinson Schweiz, Leenaards foundation, Empiris foundation, Swiss National Science foundation, Synapsis Foundation.

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Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The Cantonal Ethics commission of Geneva gave ethical approval for this work.

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Financial disclosure/conflict of interest: OB is inventor on patent US 10,286,555 B2 (Title: Robot-controlled induction of the feeling of a presence) held by the Swiss Federal Institute (EPFL) that covers the robot-controlled induction of presence hallucinations. OB is inventor on patent US 10,349,899 B2 (Title: System and method for predicting hallucinations) held by the Swiss Federal Institute (EPFL) that covers a robotic system for the prediction of hallucinations for diagnostic and therapeutic purposes. OB is cofounder and shareholder of Metaphysiks Engineering SA. OB is member of the board and shareholder of Mindmaze SA. OB, JP and FB are inventors on patent n° EP24706201.1 (Title: Numerosity estimation impairment measurement system) held by the Swiss Federal Institute (EPFL) that covers the implicit measure of presence hallucinations.

Funding sources: 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; Parkinson Schweiz, Leenaards foundation, Empiris foundation, Swiss National Science foundation, Synapsis Foundation.

All data produced in the present study are available upon reasonable request to the authors.