It’s all in your head: Pitt researchers measure hallucinations

By James Evan Bowen-Gaddy

When you think of hallucinations, you may think of a woozy feeling and swimming images or of the bright spots you see after rubbing your eyes.

Hallucinations are typically an undesired side effect of sleep deprivation, mental illness or certain prescription drugs –– called psychotropics –– but there are few ways to accurately study and measure them.

So one team of Pitt researchers gave a group of people basic hallucinations on purpose, then mapped out how their brains responded.

Bard Ermentrout of the University of Pittsburgh –– a computational biology researcher –– along with Joel Pearson of the University of South Wales and a team of four other researchers, announced in October that they were able to measure and objectively study the mental mechanisms behind hallucinations.

By inducing visual hallucinations in otherwise healthy individuals, the researchers made progress toward explaining and understanding disease-induced hallucinations, such as ones caused by Parkinson’s disease, schizophrenia and epilepsy.

To complete their study, the team induced simple hallucinations in healthy subjects by flickering high-frequency light, and then asked the subjects to compare what they saw against a physical stimulus.

“We can use flicker to study the general mechanisms of hallucinations with anybody, anytime. That means we don’t have to rely on recruiting unwell people and clinical populations,” Pearson said.

This research was a step toward being able to study the visual hallucinations associated with Parkinson’s disease, according to Pearson. For patients with Parkinson’s disease, the visual hallucinations can be debilitating, in part because it’s difficult to predict when they might strike.

Pearson said these hallucinations are also difficult to objectively quantify –– a crucial first step in scientific research –– so his most recent study opens avenues to investigate these phenomena without inconveniencing people afflicted by the disease.

The study used a well-known method of flicker-induced hallucinations, in which the researcher exposes a subject to a bright, flickering computer monitor until the subject begins to see shapes that are not there. Changing the frequency of these flickers can change the kinds of patterns subjects see.

Then Pearson and Ermentrout added their own spin. Instead of using a large flickering screen, which produces hallucinations of multiple shapes and colors, the researchers reduced the flickering space to a small ring shape. Pearson said this reduces the possibilities of hallucinations down to simple gray blobs that rotate around the ring in seemingly random directions.

In natural circumstances, hallucinations are a subjective experience, varying widely from person to person. A researcher, however, can’t make sense of hallucinations in a lab setting if those hallucinations are spontaneous and individualized.

By simplifying the hallucinations down to simple blobs, the research team minimized the subjectivity of the experiment and created hallucinations that were relatively consistent from one subject to the next.

“To do good science, we needed a simple shape,” Pearson said.

In order to study the simple hallucinations objectively, the team placed another smaller ring within the flickering one, which housed actual images of gray blobs, in addition to the hallucinated blobs. Pearson said subjects told researchers whether the hallucinated blobs were more or less pronounced than the actual images of blobs. This method of comparison allowed the team to make objective and consistent measurements, instead of relying on subjective accounts from each study participant.

“This lets us do a very basic experiment where we can see at what point people are equally likely to say the perceptual and the hallucinated blobs are the same strength,” Pearson said. “That gives us the first reliable measure of the hallucination strength.”

Ermentrout then focused most of his effort throughout the study on producing a mathematical “map” of the visual cortex during a hallucination of simple blobs. The “maps” show how the ring and hallucinated blobs appear on tissue in the visual cortex.

Ermentrout –– who has been modeling the brain since 1979 when he developed a mathematical theory of how the brain reacts to mescaline –– said his recent study made sense of the instabilities that arise in the brain during a hallucination.

“Now we can build up a real quantitative idea of how these hallucinations are formed,” Ermentrout said.

Stewart Heitmann –– who conducted postdoctoral research with Ermentrout and is a current member of the hallucination research team –– said this kind of mathematical modeling of the brain is important to developing a better understanding of visual hallucinations.

“The main claim of the paper is that an objective measure has been made of a subjective experience,” Heitmann said. “If it can glean a better understanding on [the brain’s] architecture, it gives you a better understanding of how the visual cortex works.”

The team plans to continue researching hallucinations, looking to further compare their models against quantitative data. Their major obstacle is the chaotic and personal nature of hallucinations.

“Here’s the tricky thing with science. We need something reliable to scientifically study it,” Pearson said.