Researchers map brain's signal pathways, offering new standard for diagnosing neurological disorders

South Korean researchers have developed a technology capable of tracking the direction and hierarchical structure of signal flow in the human brain, raising hopes for new diagnostic standards and tailored treatments for neurological conditions including schizophrenia, depression and chronic pain.

The National Research Foundation of Korea announced Wednesday that a joint research team led by professors Hong Seok-jun and Woo Choong-wan of Sungkyunkwan University's Department of Global Biomedical Engineering and the Institute for Basic Science's Center for Neuroscience Imaging Research had mapped the directional flow and hierarchical organization of signals across the human cerebral cortex.

The human brain operates through a complex hierarchical structure in which "bottom-up" flows carry sensory information from the outside world to higher regions, while "top-down" flows send predictive signals — based on past experience and memory — back down to lower regions.

Conventional functional MRI research, however, has largely relied on "functional connectivity," which identifies which brain regions activate simultaneously. While this approach can reveal whether regions are connected, it cannot accurately determine where a signal originates or where it travels.

To address this limitation, the research team developed "integrated effective connectivity" (iEC) technology, which combines the strengths of nine existing effective-connectivity analysis algorithms. Effective connectivity goes beyond simple co-activation to infer the directional influence one brain region exerts on another.

The team used Bayesian optimization to integrate the different algorithms. Validation against real neural data from monkeys and computer simulations showed the combined approach outperformed the best-performing single algorithm.

Applying iEC to a large brain-imaging data set of human subjects, the team reconstructed for the first time a comprehensive "signal-flow map" of the entire cerebral cortex.

The analysis revealed a clear pyramid-shaped hierarchy in the brain's information flow. Sensory-processing regions that receive external input sit at the base, regions that integrate complex information occupy the middle layer, and paralimbic areas that regulate the body's internal states and emotions sit at the top.

The study also confirmed that the brain's hierarchical structure is not fixed but shifts dynamically depending on the brain's state.

While watching a film, incoming sensory signals grow stronger, narrowing the hierarchical gap between regions and flattening the overall structure. In a state of chronic pain, by contrast, the top-down control exerted by paralimbic areas intensifies, steepening the hierarchy.

The technology has been released as open-source software, making it available for use with diverse brain-imaging data sets worldwide. The researchers believe that comparing signal flows between healthy brains and those of patients with neurological disorders could allow "signal-flow distortions" — patterns difficult to detect through conventional brain-imaging analysis — to serve as new biomarkers for individual conditions.

"This research has opened a way to directly observe the fundamental mechanisms of information processing in the living human brain," Hong said. "We expect it to make a significant contribution to diagnosing neurological disorders such as schizophrenia, depression and chronic pain, and to developing personalized treatments, through the indicator of signal-flow distortion."

The findings, supported by the Ministry of Science and ICT and the National Research Foundation of Korea, were published Tuesday in the international journal Nature Neuroscience.