A new study by researchers at Sweden’s famous Karolinksa Institute (KI) offers the first biological evidence for the link between creativity and mental illness. The study was published online in the open-access journal PLoS One and announced May 18 by KI.

Previous research has revealed that people involved in traditionally creative professions, such as artists and writers, are more likely to have a history of mental illness in their families. Likewise, creative people tend to have higher rates of illnesses such as schizophrenia and bipolar disorder. Though researchers have proposed biological mechanisms to explain the association between creativity and mental illness, no one has proved that a biological link exists until now.

To pinpoint the connection between creativity and illness, Fredrik Ullén, PhD, and his KI colleagues examined the density of dopamine receptors in the part of the brain called the thalamus. Dopamine is a neurotransmitter, a chemical that transmits messages from one neuron to another. In the thalamus, when dopamine binds to D2 receptors, it helps filter messages to the rest of the brain. Research had previously shown that people with schizophrenia have low numbers of D2 receptors, meaning that internal thoughts and ideas are not well filtered and thus can intrude on a person’s conscious thinking.

Ullén and his team suspected the same might be true of very creative people. They compared D2 receptor density with people’s scores on divergent thinking tests. People with high scores on divergent thinking are able to come up with a number of possible answers to open ended questions, such as listing all of the things a person could do with an everyday object like a brick. A higher score corresponds to higher creativity. Ullén’s group found that people with high scores on divergent thinking had low D2 receptor density, just like people with schizophrenia.

“Fewer D2 receptors in the thalamus probably means a lower degree of signal filtering, and thus a higher flow of information from the thalamus,” said Ullén, explaining that low filtering could simultaneously explain why creative people can produce so many solutions to a problem, while people with schizophrenia are bombarded by bizarre and intrusive thoughts.

“Thinking outside the box might be facilitated by having a somewhat less intact box,” noted Ullén about his new findings.