For decades, neuroscientists have puzzled over a fundamental question of human cognition: how does the same large-scale brain network seamlessly shift between deep internal thought — remembering a childhood celebration, planning next week’s work schedule, or reflecting on personal experiences — and active engagement with the outside world, such as reading a conversation partner’s facial expression or processing spoken language? Now, a team of Chinese researchers says they have resolved this longstanding mystery, uncovering a core organizational rule that governs one of the brain’s most important cognitive networks.
Led by researchers from the Institute of Psychology at the Chinese Academy of Sciences, the work centers on the default mode network (DMN), a interconnected system of brain regions that has been studied by neuroscientists for decades. For years, the scientific consensus held that the DMN was exclusively dedicated to internal cognitive processes. But newer research has challenged that view, finding that the DMN also activates during externally focused cognitive tasks, from interpreting emotional cues to parsing spoken language. Prior to this new study, no research had been able to explain how a single network could effectively carry out two seemingly conflicting roles.
To untangle this question, the research team integrated three distinct analytical approaches across multiple independent brain activity datasets: analysis of directional functional connectivity (which maps the direction of information flow between brain regions), assessment of the DMN’s intrinsic internal structure, and measurement of brain activity triggered by specific cognitive tasks. What they found upends long-held assumptions about how the DMN is organized: rather than being a single, uniform network, the DMN is actually split into two functionally distinct subregions, each specialized for a unique cognitive role.
The team’s findings, published in the leading peer-reviewed journal *Proceedings of the National Academy of Sciences* (PNAS), classify these subregions by their function: receiver-type areas and sender-type areas.
Receiver-type subregions are optimized to absorb incoming information from the outside environment, the research confirms. These areas take the lead when the brain processes external sensory input — what a person sees, hears, or experiences in their immediate surroundings — to support perception of the outside world. Sender-type subregions, by contrast, are specialized to transmit stored internal information to other brain systems. These areas draw on memories, past experiences, and internal thought to guide decision-making and action.
Using cutting-edge functional brain imaging and large-scale data analysis techniques, the team verified these distinct roles through task-based testing. When participants completed perception-focused tasks like recognizing a familiar face, receiver-type areas showed significantly higher activation. When participants relied on stored memory to make decisions, sender-type areas became the more active of the two subregions.
Zhang Meichao, the lead researcher on the project, explained that the DMN’s ability to support both external perception and internal cognition directly stems from this natural structural division into functionally distinct sender and receiver zones. This organizational framework allows the brain to shift smoothly between internal thought processes and engagement with the external world without conflict or cognitive overload.
Zhang added that this breakthrough offers a new, simplified framework for understanding how the brain’s association cortex — the region responsible for high-order cognitive functions including complex thinking and flexible cognition — enables seamless transitions between internal reflection and interaction with the surrounding environment. The discovery lays a critical foundation for future research into cognitive processing, and may open new avenues for understanding neurological conditions that impact cognitive flexibility.