Scientists map the hidden architecture of the brain’s default mode network

A new study published in Nature Neuroscience sheds light on the structural foundations of the brain’s default mode network, a system of regions long associated with internally focused thought, memory, and self-reflection.

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Using postmortem brain tissue and advanced neuroimaging, researchers found that this network is composed of distinct anatomical types of brain tissue, each with different roles in processing information. The findings help explain why the default mode network is involved in such a wide variety of mental states—from introspection to decision-making—and suggest that its structure enables a unique balance of communication across the brain.

The default mode network, or DMN, is one of the most widely studied yet poorly understood brain systems in neuroscience. It was originally discovered through brain scans showing that certain regions become less active when a person focuses on an external task, like solving a math problem. But over time, researchers noticed these same regions were also active during a wide range of cognitive activities, such as daydreaming, remembering the past, imagining the future, and even making complex decisions. This unexpected versatility raised fundamental questions about what the DMN does and how it manages to participate in such seemingly contradictory mental functions.

One key to solving this puzzle, the researchers hypothesized, lies in the network’s anatomy. Much of the past research on the DMN has used functional MRI to track patterns of activity, but less attention has been paid to the underlying microstructure that might shape those functions. The authors of the new study believed that a deeper understanding of the DMN's cellular and anatomical features could clarify how it supports such a diverse array of mental processes.

“The default mode network has a fascinating history in neuroscience. It was first identified as a group of brain regions that become less active when people engage in a specific task,” explained study author Casey Paquola, the head of the Multiscale Neurodevelopment Lab at the Institute of Neuroscience and Medicine (INM-7) at the Helmholtz Associations’ Research Center Julich.