Neuroscientists at MIT have found clear evidence that the brain contains flexible modules of neurons capable of performing the same basic computation on different kinds of information. In a study of mice, they identified clusters of cells in the prefrontal cortex that can hold either a sensory stimulus or a planned action in working memory. The prefrontal cortex is a brain region involved in planning, decision-making, and other executive functions.
The discovery supports a long-standing idea that the brain reuses the same neural circuits across many situations rather than building a separate set of cells for every possible case. This modularity may help explain how a limited number of neurons can support the wide range of cognitive abilities people and animals show every day. Researchers trained mice on a task that required them to hear two tones, decide whether the tones matched, and then respond with a specific action. While the animals performed the task, electrical activity was recorded from thousands of neurons in the prefrontal cortex and the parietal cortex. The parietal cortex processes sensory information and helps plan movements.
Analysis of the recordings revealed that neurons in the parietal cortex mainly stored memory of the tone itself. In the prefrontal cortex, however, a particular group of neurons switched roles. During the interval after the first tone, these cells held the memory of that tone. Later, after the second tone but before the response, the same cells stored the planned action instead.
Flexible reuse of neural circuits
This ability to repurpose the same population of neurons allows the brain to mix and match computational building blocks as needed. The findings suggest that animals and humans do not have to construct an entirely new circuit every time they learn a new task or need to hold a different kind of information in mind. Instead, existing modules can be flexibly assigned to whatever content is required at that moment. The researchers plan further experiments to test whether temporarily disrupting these modules alters the animals’ performance, which would provide additional support for their functional role.
This research is published in Nature Neuroscience.