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EPFL neuroscientists have devised a way to alter our social perception and monitor specific types of hallucinations, both in healthy individuals and patients with Parkinson's disease. The test, which is also available online, provides the medical community with a tool to monitor hallucination susceptibility.
If you had to estimate the number of people in a room, without counting them one-by-one, by nature you would overcount them. That's because, simply put from a Darwinian perspective of how we have evolved, it's better to overcount potentially harmful agents and predators than to underestimate them. This overcounting social behaviour is shown to be true in humans as well as animals. It's certainly better to detect too many tigers (even if absent) during a jungle excursion than to miss a hungry one!
Now, EPFL neuroscientists show that if you experience hallucinations, especially when related to an illness like Parkinson's disease, then you will over-estimate the number of people in a room to a greater degree. They also show that if you have hallucinations but are asked to estimate the number of boxes in a room, which are inanimate control objects, then no extra over-estimation occurs, shedding light on the social nature of this overcounting. The results are published in Nature Communications.
"The fact that patients of Parkinson's disease have a much higher over-estimation in counting people is mind-blowing because Parkinson's disease is classically viewed as a movement disorder," says Olaf Blanke who leads EPFL's Laboratory of Cognitive Neuroscience which is part of Neuro-X. "We show that Parkinson's may also be a perceptual disorder, especially of social stimuli, and that invisible presences in Parkinson's Disease may impair even more the counting social brain!"
The category of hallucinations investigated by the neuroscientists is called presence hallucinations, for which people report an invisible presence next to them, even though no-one is there. Such hallucinations are considered to be minor compared to visual hallucinations for instance. They may be experienced early on in patients with Parkinson's disease, sometimes even before diagnosis. Presence hallucinations are also a known early marker of cognitive decline in Parkinson's disease.
The results of the study support the idea that the invisible presence (and
