The Role of Temporal Processing in Induced Presence Hallucinations
© LNCO / EPFL 2022
Led by Herberto Dhanis and Dr Eva Blondiaux this study on robotically-induced hallucinations has revealed novel insights into the neural mechanisms behind the induction of Presence Hallucinations, and Passivity experiences, by taking a closer look at the temporal relationships between distributed brain networks. Presence hallucinations are of major clinical importance and the most frequent hallucination in early Parkinson’s disease.
As the authors explain in their article now published in NeuroImage, when a healthy person is sensitive to the induction of Presence Hallucination, the brain highly favours one brain network, having all other networks transition more to it over time. In contrast, if a healthy person is sensitive to Passivity Experiences, the brain will avoid one other specific brain network, having all brain network decrease the transitions to it over time. These data reveal specific temporal relationships of brain networks for a specific hallucination that is of relevance for the early detection of Parkinson’s disease.
Abstract The perception that someone is nearby, although nobody can be seen or heard, is called presence hallucination (PH). Being a frequent hallucination in patients with Parkinson's disease, it has been argued to be indicative of a more severe and rapidly advancing form of the disease, associated with psychosis and cognitive decline. PH may also occur in healthy individuals and has recently been experimentally induced, in a controlled manner during fMRI, using MR-compatible robotics and sensorimotor stimulation. Previous neuroimaging correlates of such robot-induced PH, based on conventional time-averaged fMRI analysis, identified altered activity in the posterior superior temporal sulcus and inferior frontal gyrus in healthy individuals. However, no link with the strength of the robot-induced PH was observed, and such activations were also associated with other sensations induced by robotic stimulation. Here we leverage recent advances in dynamic functional connectivity, which have been applied to different psychiatric conditions, to decompose fMRI data during PH-induction into a set of co-activation patterns that are tracked over time, as to characterize their occupancies, durations, and transitions. Our results reveal that, when PH is induced, the identified brain patterns significantly and selectively increase their transition probabilities towards a specific brain pattern, centred on the posterior superior temporal sulcus, angular gyrus, dorso-lateral prefrontal cortex, and middle prefrontal cortex. This change is not observed in any other control conditions, nor is it observed in association with other sensations induced by robotic stimulation. The present findings describe the neural mechanisms of PH in healthy individuals and identify a specific disruption of the dynamics of network interactions, extending previously reported network dysfunctions in psychotic patients with hallucinations to an induced robot-controlled specific hallucination in healthy individuals.
The Bertarelli Foundation Catalyst Fund (no. 532024)
The Swiss National Science Foundation NCCR “Synapsy The Synaptic Bases of Mental Diseases” (no. 51NF40-185897)
Two donors advised by Carigest SA, including the Fondazione Teofilo Rossi di Montelera e di Premuda.