New method to study hallucinations causes us to see 'pale grey blobs'

Scientists have come up with a new method to induce and measure visual hallucinations. They hope their model will shed light on how these complex experiences form in the human brain, whether in healthy individuals or in people suffering from psychiatric disorders.

Hallucinations have always fascinated neuroscientists and psychiatrists. While they are often associated with mental health issues, visual hallucinations can also occur in healthy people – especially if they are under the influence of drugs, are lacking sleep or suffering from migraine. In these different contexts, the brain undergoes small changes, and it is thought that this leads to the disruption of normal visual perception and thus, to hallucinations.

However the underlying mechanisms are still not very well understood. Research on visual hallucinations is often hampered by the fact they occur unexpectedly, and are different from one person to another.

One of the main challenges in the field has been to induce hallucinations in controlled scientific settings that are stable and identical for all people.

Scientists indeed struggle to trigger hallucinations whenever and however they want to in the lab, and the content of these hallucinations is inherently subjective. The lack of homogeneity between research participants makes it hard to identify the mechanisms in our brain that cause hallucinations. The new study, published in eLife, presents a new method to induce visual hallucinations in order to study them in more details.

Big 'grey blobs'

The initial aim of the research, conducted by researchers from the University of New South Wales (Australia), was to come up with a method to trigger hallucinations and to make sure they were the same for all participants. "We have known for more than 100 years that flickering light can cause almost anyone to experience a hallucination," says UNSW Associate Professor Joel Pearson, who led the study.

With his team, he used a flickering ring of white light against a black backdrop – as seen on the video below. This induced visual hallucinations in a number of healthy volunteers, causing all of them to see the same hallucinatory image of "pale grey blobs".

Warning: It is recommended that anyone with a history of migraines, epilepsy or psychiatric disorders refrain from watching the video below.

"With our technique we get rid of the unpredictability. People don't see windmills, lines, or different colours; they just hallucinate grey blobs. Once the hallucination is stable like this, with just the blobs, we can start to objectively investigate the underlying mechanisms," says Pearson.

Once the hallucinations were triggered, the scientists measured their strength. They placed a second ring, marked with permanent grey blobs, inside the white ring. The participants had to say whether the hallucinated blobs were lighter or darker than the real blobs, thus communicating how strong their hallucinations were.

The next step of this research will be to apply these methods to people with psychiatric or neurological diseases. For this purpose, the team has begun working with people with Parkinson's disease.

"Not everyone who gets Parkinson's has hallucinations. If we can use these models to study their hallucinations, we can find out what might be causing them, and hopefully learn more about other symptoms that accompany natural hallucinogenic states," Pearson concluded.