The CogLinks model reveals how the brain adapts to rule changes

Every day, your brain makes thousands of decisions under uncertainty. Most of the time, you guess right. When you don’t, you learn. But when the brain’s ability to judge context or assign meaning falters, thoughts and behavior can go astray. In psychiatric disorders ranging from attention-deficit/hyperactivity disorder to schizophrenia, the brain can misjudge how much evidence it needs to gather before acting—or fail to adjust when the rules of the world change based on new information.

Uncertainty is built into the brain’s wiring. Imagine groups of neurons that cast votes—some optimistic, some pessimistic. Your decisions reflect the average.” When this balance is out of whack, the brain can misinterpret the world: ascribing too much meaning to random events, as in schizophrenia, or clinging to rigid patterns, as in obsessive-compulsive disorder.

Understanding these failures has long challenged scientists. The brain speaks the language of individual neurons. But fMRI – the tool we use to study brain activity in humans – monitors blood flow, not the electrical chatter of individual brain cells.”

Michael Halassa, professor of neuroscience, Tufts University School of Medicine

Bridging this gap means combining insights from single-cell animal studies, human brain imaging, and behavior. Now, a new kind of computational model based on real biology allows researchers to simulate how brain circuits make decisions and adapt when the rules change.

They called CogLinksthe model incorporates biological realism into its design, reflecting how real brain cells are wired and encoding how they assign value to often ambiguous and incomplete observations about the external environment. Unlike many AI systems that act like “black boxes”, CogLinks shows researchers exactly how his virtual neurons link structure to function. As a result, scientists can map how this virtual brain learns from experience and pivots based on new information.

In one study published on October 16 at Nature communicationssenior author Halassa and colleagues at the Massachusetts Institute of Technology (MIT) used CogLinks to explore how brain circuits coordinate flexible thinking. Like a flight simulator for the brain, CogLinks leave researchers test what happens when basic decision-making circuits go off course. When they weakened the virtual connection between two simulated brain regions—the prefrontal cortex and the medial thalamus—the system learned more slowly by habit. This result suggests this pathway is essential for adaptability.

To see if these predictions held true in humans, the team then conducted an accompanying fMRI study, which they both supervised Burkhard Pleger from the Ruhr-University Bochum and Halassa. The volunteers played a game in which the rules were unexpectedly changed. As expected, the prefrontal cortex handled planning and the deep, central region of the brain known as striatum-driven habits—but the medial thalamus lit up when the players realized the rules had changed and adjusted their strategy.

The imaging confirmed what the model predicted: the medial thalamus acts as a switchboard connecting the brain’s two main learning systems—flexible and habitual—helping the brain infer when the context has changed and change strategies accordingly.

Halassa hopes the research will help lay the groundwork for a new kind of “algorithmic psychiatry“, in which computer models are helping to reveal how mental illness emerges from changes in brain circuits, identifying biological markers to precisely target treatments.

“One of the big questions in psychiatry is how to connect what we know about genetics to cognitive symptoms,” he says. Style Brabeeba Wang, its main author CogLinks study, co-authored by fMRI studies and PhD student at MIT in Halassa’s lab.

“Many mutations linked to schizophrenia affect chemical receptors found throughout the brain,” says Wang. “Future uses of it CogLinks may help us see how these widespread molecular changes could make it harder for the brain to organize information for flexible thinking.”