A new study has identified a neural network in the brain responsible for hallucinations and reports a new robotic diagnostic tool that captures sensory and motor processing through brain imaging to determine the severity of the progression of the disease by safely provoking such hallucinations in Parkinson’s Disease (PD) patients.

Scientists at the École polytechnique fédérale de Lausanne (EPFL) in Switzerland have published the findings of their three-tier study on 56 PD patients from centers in Switzerland and Spain, in the journal Science Translational Medicine (STM), in an article titled “Robot-induced hallucinations in Parkinson’s disease depend on altered sensorimotor processing in frontotemporal network.

“We’re developing something similar to a cardiac stress test, but instead of testing the heart, we’re testing the brain,” says Olaf Blanke, PhD, neuroscientist at the EPFL and senior author on the study.

Olaf Blanke, PhD, neuroscientist at the EPFL and senior author on the study

In addition to slowness of movement, muscle stiffness, and uncontrollable shaking of the limbs, PD patients may also experience mental symptoms like psychosis, depression, apathy, cognitive decline and even dementia. These are undiagnosed or underdiagnosed because patients are reluctant to report them to their doctors, and clinicians often fail to ask about them or lack tools to assess them. Hallucinations in PD constitute a major risk factor for psychosis and dementia.

Nearly 50% Parkinson’s Disease patients experience “presence hallucinations.” These can feel like someone is standing behind you, fleeting movements of people or animals in the peripheral vision, or realistic technicolor sights.

In an earlier study, Blanke reported when normal individuals were subjected to a robotic procedure, using specific movements and somatosensory signals, they report feelings of being accompanied by a presence or person.

In the current study, Blanke’s team first establishes an improved version of the earlier brain stress test to induce presence hallucinations in patients with PD. In this test, the participant makes repeated poking gestures that are duplicated by a robotic arm on the patient’s back.

When the human and robotic movements are in synchrony the brain successfully computes the spatial dissonance and can make sense of the situation. But when the movements are out of synchrony, healthy participants and PD patients report presence hallucinations. Patients who have already experienced presence hallucinations show a higher sensitivity to robotic stimulations compared to patients with no prior hallucinations.

Eva Blondiaux, co-first author of the study

In the second tier of the study, the investigators identified the neural network responsible for presence hallucinations in healthy patients. This “presence hallucination network,” the authors report, includes three regions in the fronto-temporal cortex of the brain: the inferior frontal gyrus, the ventral premotor-cortex and the posterior middle temporal gyrus.

In the final part of the study, the scientists accurately predict the severity of the patients’ symptoms in a group of 30 new PD patients using the brain stress test.

“Adapting the robotic device and procedure to the scanner allowed us to identify a brain network that is relevant for presence hallucinations in patients with Parkinson’s disease and that could potentially serve as a biomarker for more severe forms of the disease associated with hallucinations and cognitive deficits,” says Eva Blondiaux, PhD student and co-first author on the study.

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