Study offers single explanation for two major symptoms of schizophrenia

Publishing in the Journal of Neuroscience, researchers at Stockholm's KTH Royal Institute of Technology and University of Tokyo, Japan found that problems with motivation and the formation of delusional beliefs may both be linked to a single underlying problem: when an overactivated cortex disrupts the brain's ability to link actions and consequences.

Arvind Kumar, associate professor in computational neuroscience at KTH, says the study offers a computational neuroscience model that attempts to unify several known roles of the brain's dopamine system: learning from rewards, controlling motivation and building an internal picture of what's going on.

A unified explanation would make it easier to study how these symptoms develop together and may guide future research into treatments, says lead author Kenji Morita, associate professor at University of Tokyo. “If the suggested root cause is validated, then mechanistically grounded therapies could be developed," Morita says.

The model in the study shows what happens when this internal cause-and-effect tracking system breaks down. The model suggests that two simultaneous learning processes in the cortico-basal ganglia-midbrain circuits need to align for a person to realize what is rewarding and why.

Deep within the brain, the striatum is a control center that enables the brain to learn which reward is which and selectively increase motivation for right one, such as food when hungry or water when thirsty.

The other dopamine alignment takes place in the cortex. This is the part that enables the brain to essentially follow what is happening. It enables the brain to assign credit correctly: for example, a smell of baked bread predicts food, or the sound of liquid predicts drink.

The researchers found that both reduced motivation and delusion‑like beliefs could arise when an overstimulated cortex disrupts alignment between these processes.

"It causes the brain's learning system to mix up association between motivation and reward," Kumar says, "leading to both low motivation and delusion‑like ideas, such as assigning the wrong reasons for things happening."

"The brain needs to align motivation, reward identity and their causes together to make a suitable choice," he says.