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The human brain is remarkably adept at juggling different kinds of information, allowing us to switch rapidly between tasks and adapt our behavior as circumstances change. A new study by MIT neuroscientists takes a closer look at how the brain accomplishes this, providing evidence for flexible neural modules that may help support this cognitive versatility.

Using mice, scientists found that a group of neurons in the prefrontal cortex could switch between retaining sensory information and maintaining an action plan in working memory.

“We found that the brain doesn’t dedicate a separate group of neurons for every type of information,” says Yuma Osako, an MIT postdoc and the lead author of the new study. “Instead, it uses the same populations of neurons to perform the same computation on different kinds of information, which means the same subset of neurons can hold both an action and a sensory stimulus in working memory,”

The findings also lend support to a longstanding theory known as compositionality—the idea that cognition can be constructed by combining and reusing neural components.

“One of the solutions that’s always been proposed has been this idea of compositionality — that you can take pieces of cognition that perform part of a task and reuse them in another task,” says Timothy Buschman, a professor at the Princeton Neuroscience Institute, and the senior author of the paper, in a statement. 

Another way to see this is to view it as “cognitive Legos,” Buschman suggests. Instead of building a new neural circuit when a new task starts, the brain reuses existing circuits and combines them in different ways.

The Test 

To see how this neural network operates, the scientists trained mice to compare two tones and respond depending on whether the sounds matched. As the mice performed the tasks, the scientists recorded electrical activity from thousands of neurons. 

“When mice do tasks that test whether memory computations can be reused, the answer is they are,” notes Mriganka Sur, the Newton Professor of Neuroscience at MIT’s Picower Institute for Learning and Memory. “There are subspaces of functional activity in the prefrontal cortex that can be the substrate of mixing and matching toward flexible cognition.”

Two important components of the task allowed the researchers to examine how different kinds of information were maintained. First, the mice had to remember the initial tone for a short period. They then had to retain their decision and form an action plan.

In the parietal cortex, neurons were dedicated to storing information about the tone. However, researchers found something different in the prefrontal cortex: a specific group of neurons could switch roles.

During one stage of the task, the circuit helped maintain a sensory memory. During another, the same population was involved in maintaining an action plan. This flexibility may help explain how a finite number of neurons can support an enormous range of behaviors.

“Our everyday life requires us to temporarily hold many different kinds of information. One big question is how the brain can represent an unlimited variability of information using only a finite number of neurons,” Osako says.

The researchers view these reusable neural circuits as potential building blocks for flexible cognition. More broadly, the findings suggest that the brain may be less like a machine filled with components dedicated to individual tasks and more like an interconnected system that continually repurposes its existing neural resources.

The recent study appeared in the journal Nature.

Chrissy Newton is a PR professional and the founder of VOCAB Communications. She currently appears on The Discovery Channel and Max and hosts the Rebelliously Curious podcast, which can be found on YouTube and on all audio podcast streaming platforms. Follow her on X: @ChrissyNewton, Instagram: @BeingChrissyNewton, and chrissynewton.com. To contact Chrissy with a story, please email chrissy @ thedebrief.org.