Just as doctors conduct blood tests to check patients’ heart health, scientists run tests on people’s brains to better understand how they function and how to treat certain mental disorders. Unlike other organs, however, the brain is widely mysterious. Little is known about how humans develop these disorders, let alone why. But a new study claims it’s made a leap forward in that sense of understanding, as researchers have observed particular brain activity according to simple learning errors.
The present study is far away from clinically significant processes, concedes Klaas Stephan, a professor of translational neuroscience modeling at ETH and the University of Zurich. However, he and his colleagues believe the findings could help scientists better understand why, for instance, certain forms of mental illness, such as schizophrenia, require one type of medication over another. The answer, they suggest, could be found in the way human brains respond to errors in associative learning.
Associative learning invokes pairing certain information with other, unrelated data to cognitively draw a link between the two. In the current study, the team of researchers had subjects listen to either a high-pitched tone or low-pitched tone, before predicting which image would follow: a house or a face. Experimenters rigged the experiment so a house would initially follow a high-pitched tone 70 percent of the time. Meanwhile, they observed the brain activity of each subject as they performed the task to see how their brains lit up when they made a mistake.
Mistakes of associative learning largely ignited the midbrain. Neurons in this region communicate via the neurotransmitter dopamine, which most popularly plays a role in the limbic system’s “pleasure center” of the brain. It’s the neurotransmitter responsible for gratification, sex, and rats dying of exhaustion because they’d rather experience intense pleasure than eat.
But this isn’t what the team found through their trials.
“These results included a significant activation in the dopaminergic midbrain in both studies,” said Sandra Iglesias, postgraduate fellow at the University. “This finding is remarkable because the prediction error concerned a purely sensory event, not rewards or novelty. This has nothing to do with gratification.”
Science has long believed that learning processes activated these dopaminergic neurons, yet the team’s study suggests the opposite. They also found within their study that the basal forebrain, a part of the brain that produces and distributes the neurotransmitter acetylcholine throughout the body, got activated when subjects made more errors in prediction. Acetylcholine helps brain cells communicate with one another, making it critically important in learning.
Further research is required to better understand how certain parts of the brain react when a person is confronted with non-gratification-based stimuli. Mental disorders, for example, may require specific treatment options depending on how the brain’s various regions light up in an fMRI (functional magnetic resonant imaging) scanner.
“If we can use this kind of method, for example, to show that one sub-type of schizophrenia instead of another is related to a disorder in the dopaminergic signal systems of the brain, it will have a bearing on which medication should be administered,” Stephan said. “This will bring us one step closer to the clinically relevant processes.”
Source: Iglesias S, Mathys C, Brodersen K. Hierarchical Prediction Errors in Midbrain and Basal Forebrain during Sensory Learning. Neuron. 2013.