Creativity often goes hand-in-hand with mental illness, such as schizophrenia. Now scientists think they know why: The brain responds differently to the "feel good" chemical dopamine in both schizophrenics and the highly creative, a new study suggests.

The results showed similarities between the brains in healthy, highly creative people and those with schizophrenia. The findings suggest that creative types might not be able to filter information in their heads as well as "normal" folks, leaving them better able to make novel connections and generate unique ideas.

"Thinking outside the box might be facilitated by having a somewhat less intact box," said study researcher Fredrik Ullén, of the Karolinska Institutet in Stockholm, Sweden.

Studies have found that creative skills are more common in people who have mental illness in their families, and are associated with a higher risk of schizophrenia and bipolar disorder. Also, certain psychological traits, such as the ability to make unusual or bizarre associations are shared by schizophrenics and healthy, highly creative people.

Some research has also found an association between creative abilities and the brain's dopamine system — the network of neurons set up to respond to dopamine. (Dopamine is a neurotransmitter that, amongst other things, is involved in the reward response to everything from chocolate to cocaine.) However, the mechanism behind the dopamine-creativity link was largely a mystery.

Ullén and his colleagues administered psychological tests to 14 participants with no history of mental illness. The tests were designed to measure creativity, asking the subjects to find many different solutions to a problem.

Those who did well on this test, and were deemed "highly creative," had a lower density of specific receptors in their brains for dopamine, called D2 receptors, in a region called the thalamus, than did less creative people, according to Ullén.

"Schizophrenics are also known to have low D2 density in this part of the brain, suggesting a cause of the link between mental illness and creativity," he said.

The thalamus serves as a kind of relay center, filtering information before it reaches areas of the cortex, which is responsible, amongst other things, for cognition and reasoning.

"Fewer D2 receptors in the thalamus probably means a lower degree of signal filtering, and thus a higher flow of information from the thalamus," Ullén said, and explains that this could a possible mechanism behind the ability of healthy highly creative people to see numerous uncommon connections in a problem-solving situation and the bizarre associations found in the mentally ill.

The results were published online May 17 in the journal PLoS ONE.