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We all have "presence hallucinations," but what causes them?

Neuroscientists from EPFL have shed light on a fascinating aspect of human and animal behavior called “presence hallucinations” — the tendency to overestimate numbers, particularly in social settings.

This behavior, deeply rooted in our evolutionary past, serves as a protective mechanism, ensuring we err on the side of caution by overestimating potential threats, such as predators.

Imagine walking through a jungle. It’s far safer to assume there are more tigers lurking than there actually are. This innate behavior transcends species, highlighting a fundamental survival strategy.

How overcounting relates to Parkinson’s disease

The study, recently published in Nature Communications, ventures into the realm of hallucinations associated with illnesses like Parkinson’s disease, revealing that those experiencing such hallucinations tend to overestimate the number of people in a room even more significantly.

Interestingly, this heightened overestimation does not extend to inanimate objects, such as boxes, suggesting a uniquely social dimension to this phenomenon.

Olaf Blanke, leading the Laboratory of Cognitive Neuroscience at EPFL and a part of Neuro-X, expressed astonishment at the findings.

“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 Blanke. “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!”

Prescence hallucinations and their role in social overcounting

The study focuses on “presence hallucinations,” where individuals feel an invisible entity nearby, despite no one being present. These hallucinations, often minor compared to visual ones, can appear early in Parkinson’s disease, sometimes predating diagnosis, and serve as an early indicator of cognitive decline.

Researchers propose that the sensation of an invisible presence, likely due to specific brain mechanisms, contributes to the overestimation of people.

This “extra presence” is subconsciously added to the count but only when estimating the number of people, not objects. This discovery underscores the social nature of our perceptual systems and their susceptibility to disorders like Parkinson’s.

Technodelics: Merging VR and robotics

To explore this theory, the team employed a novel approach, merging virtual reality with robotics in a method they dub “technodelics.” This innovative combination creates technology-induced altered states of consciousness and hallucinations.

In their experiments, participants were shown brief 3D scenes of varying numbers of people and experienced artificial presence hallucinations via a robotic finger. This setup not only induced hallucinations but also provided a measurable indication of an individual’s susceptibility to them.

“The advantage of our technodelics environment is that it gives us an objective way to measure hallucinations which are highly subjective states,” explains Louis Albert, lead author of the study. “We are essentially engineering hallucinations, inducing hallucinations and getting a clear, implicit read-out of hallucination susceptibility at a given time.” 

Testing presence hallucinations with virtual worlds

This research has led to the development of a simplified, online version of their experiment, allowing for unobtrusive testing from home. This breakthrough offers a significant advancement in assessing hallucination susceptibility, especially in Parkinson’s disease patients, without the need for specialized equipment or personnel.

“The test can be carried out independently by patients, directly from home on their computer or tablet, thus has the potential to reach a large demographic at minimal cost,” Albert said.

“Without the need for patients to travel to the clinic, this test is accessible and can reach people living far away from medical centers and in low-income countries,” he concluded.

What the scientists learned

With around 170 Parkinson’s disease patients participating in the online test, including 69 with presence hallucinations, the study confirmed that those experiencing these hallucinations tend to overcount more. Remarkably, some reported seeing as many as 11 or more people in scenes showing only eight.

Fosco Bernasconi, a co-author of the study, highlighted the clinical implications of their findings. “We have strategies for determining if a patient with Parkinson’s disease experiences presence hallucinations or not, which means that in the future we should be able to identify and monitor those who are more prone to cognitive decline for early treatment.”

Redefining perception and the future of Parkinson’s care

In summary, EPFL neuroscientists have revolutionized our understanding of the human tendency to overcount in social settings. In their study, they linked this phenomenon to the “presence hallucinations” often experienced by individuals with Parkinson’s disease.

Through innovative technodelic experiments merging virtual reality with robotics, they were able to showcase the social nature of our perceptual inaccuracies and opened new avenues for diagnosing and treating cognitive impairments early on.

This fascinating and important research challenges our traditional views of Parkinson’s disease while providing a hope for those affected, promising more personalized and effective interventions in the future.

More about Parkinson’s disease and presence hallucinations

As discussed above, Parkinson’s disease primarily stems from the loss of dopamine-producing neurons in a region of the brain called the substantia nigra. Dopamine acts as a messenger that coordinates smooth and balanced muscle movements. Why these neurons deteriorate remains largely unknown, but researchers believe a combination of genetic and environmental factors plays a critical role.

Symptoms beyond the shakes

While tremors are among the most visible symptoms of Parkinson’s disease, the condition manifests in several other ways, including through presence hallucinations.

  • Rigidity and Bradykinesia: Patients often experience stiffness and slowness in movement, making daily tasks challenging.
  • Postural Instability: Balance problems and falls are common, stemming from the disease’s impact on motor control.
  • Cognitive and Emotional Changes: Many individuals face difficulties with memory, problem-solving, and emotional regulation, including depression and anxiety.

Innovations in treatment

Treatment for Parkinson’s disease is highly individualized, aiming to manage symptoms and improve quality of life. The most common treatments include:

  • Medication: Drugs like Levodopa increase dopamine levels in the brain, alleviating motor symptoms. Other medications target specific symptoms, such as tremors or rigidity.
  • Physical Therapy: Tailored exercise programs help maintain mobility and balance, addressing the physical challenges of the disease.
  • Deep Brain Stimulation (DBS): For some patients, this surgical procedure can significantly reduce symptoms by implanting electrodes in specific brain regions to regulate abnormal impulses.

Future of Parkinson’s care and treating presence hallucinations

Research into Parkinson’s disease is ongoing, with scientists exploring genetic markers, environmental triggers, and new treatment modalities. Recent advancements in neuroimaging and molecular biology hold promise for early diagnosis and more targeted therapies. As understanding of the disease deepens, the hope for better management strategies and ultimately a cure continues to grow.

In summary, Parkinson’s disease is a complex condition with far-reaching effects on individuals’ lives. While there is no cure yet, advancements in treatment and care offer hope and improved outcomes for those affected. By staying informed and proactive, patients and caregivers can navigate the challenges of Parkinson’s disease with resilience and determination.

The full study was published in the journal Nature Communications.


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