According to the Parkinson’s Disease Foundation, almost one million Americans suffer from the progressive movement disorder. There is no standard test to diagnose Parkinson’s, so doctors must rely on clinical or neurological exams—and since many other conditions such as strokes have symptoms similar to Parkinson’s, it can be very difficult to confirm a diagnosis.
Could an eye test developed to induce hallucinations be the answer?
Dr. Bard Ermentrout, a professor of mathematics and computational biology at the University of Pittsburgh, collaborated with researchers at Australia’s University of New South Wales to develop a new method for creating visual hallucinations. Since hallucinations are a hallmark of Parkinson’s disease, using a test similar to the one in this study could help determine whether a patient has (or doesn’t have) the disorder.
While drug-induced hallucinations alter the brain’s internal dynamics so that patients hear voices or see objects that aren’t there, the Pitt/NSW study (which was published in the journal eLife) focused on geometric hallucinations, in which people perceive geometric patterns (such as checkerboards or zigzags) floating in front of their eyes.
“There are no giant purple Elvises or Cadillacs falling through the sky,” Ermentrout told the Observer. “The pathologies are the same, but it’s different from hearing voices.”
Ermentrout’s Australian collaborators experimented with geometric hallucinations using the full field flicker method, which tests physical sensitivity to visual stimuli.
“There are bright and intense geometric patterns, which are constantly changing,” Ermentrout (who did the statistical analysis after the experiment) said.
The study subjects watched a flickering ring (above) and then reported how many blobs they saw pulsing around it (in reality there were none) along with how fast those hallucinatory blobs were moving. Researchers then held up drawings of the circle and blobs, and asked them to identify the one that looked most similar to what they saw (each picture had a different number of blobs going around the circle).
Participants were then shown a ring with actual gray blobs around it (above), and were able to rate the strength of the hallucinations by indicating whether the hallucinated blobs were lighter or darker than the real blobs.
“Hallucinations change rapidly, but we wanted to quantify them,” Ermentrout said. “It was a test of what you saw as opposed to what you should see.”
The researchers found that the patterns of the real blobs and hallucinations were so similar that the subjects’ brains couldn’t actually tell the difference between them, and also that both the hallucination and the blob seemed to move left to right (a phenomenon called perceptual bistability—many optical illusions follow the same pattern).
As the study authors point out, this experiment was very simple, employing a one dimensional ring and one set of blobs. But they also write that a model like this could be useful in determining the “range of non-ordinary function” that produces hallucinations.
Analyzing these functions could lead indirectly to a method of diagnosing Parkinson’s disease. The study team is recruiting Parkinson’s patients with visual hallucinations to see how they respond to the flickering ring—Ermentrout called this a “noninvasive probe” of the disease.
“For example, they may be more sensitive or respond at different frequencies from normal subjects,” Ermentrout said. “By using this reduced stimulus to study hallucinations in psychiatric disorders, we may be able to better pinpoint both the onset and the origin of these effects. “
