The Brain

Scientists have found how to make people hallucinate, and how to measure what they see

The ConversationHow can we measure the mind? When you ask someone what they’re thinking about, what they tell you is not necessarily the truth. This doesn’t mean they’re lying. It means many environmental, social and personal influences can change what someone tells us.

If I put on a white lab coat, suit or t-shirt and ask you a bunch of questions, what I wear will change what you say. This was demonstrated in the famous Milgrim experiments in the 1960s, which showed the power of perceived authority to control others’ behaviours. People want to be liked, or give a certain impression. This is commonly referred to as impression management and is one of the hardest obstacles to overcome in scientific research.

Neuroscientists have made notable advances in measuring the anatomy of the brain and its regions at different scales. But they’ve made few big advances in measuring the mind, which is what people think, feel and experience. The mind is notoriously difficult to measure; but it needs to be done as it will aid development of new treatments for mental and neurological disorders.

Out-of-control mental imagery and hallucinations are good examples of mental health symptoms that are difficult to measure accurately in science and medicine. Our study published this week shows a new method to induce and measure visual hallucinations in anyone at any time.

These findings open the door to a new avenue of research. We can now study visual hallucinations in the lab using anyone as a subject.

What are hallucinations?

Hallucinations are commonly associated with disorders such as schizophrenia and Parkinson’s disease. But healthy people can also have visual hallucinations after taking drugs, being sleep deprived or suffering migraines, just to name a few conditions.

Video by Joel Pearson

Generally, hallucinations are defined as an involuntary perception-like experience in the absence of an appropriate direct stimulus. To put it more simply, seeing or hearing something that isn’t there. Hallucinations can range from simple geometric shapes, such as blobs, lines and hexagons, to seeing animals, people or insects.

These involuntary experiences are thought to come about when spontaneous changes in the brain temporarily hijack vision and attention, but the exact causes and underlying mechanisms aren’t fully understood. The best way to understand these things, is to induce a hallucination and observe it in a laboratory.

We have known for more than 200 years that flickering light at particular frequencies can cause almost anyone to experience hallucinations. But the unpredictability, complexity and personal nature of these make them difficult to measure scientifically without having to rely on verbal descriptions. Their changing content, including colours and changing shapes, add to the difficulty.

The simple breakthrough in our research was to reduce hallucinations from flickering lights to a solitary dimension: grey blobs. To do this, rather than flashing random lights or a full computer or TV screen on and off, we flickered a doughnut ring shape instead.

To our surprise, when we did this, we no longer saw lots of different shapes and colours but just grey blobs. By reliably stabilising the hallucination in this way, we could start to objectively investigate its underlying mechanisms.

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