Organized When Awake, Chaotic When Not

Researchers

Overview

Kyoto, Japan -- How and why we experience consciousness is a question that has long plagued philosophers and scientists alike. We have come to understand that when awake our brains organize neural information for perception, yet we completely lose this organization under anesthesia. Why this happens is a longstanding mystery in neuroscience, as simple changes in the activity levels of specific brain regions fail to explain this disappearance of consciousness.

Theories have hypothesized that conscious perception arises from two core pillars: the brain's ability to encode external features, and its ability to transmit information across different cortical regions. While the former has been well-supported, direct physical evidence of the latter has remained elusive. A team of researchers at Kyoto University set out to bridge this critical gap between neural signals and information dynamics.

The team developed arrays for high-density custom electrocorticography -- or ECoG -- that covered most of the cerebral cortex of a rat's right hemisphere. This allowed them to extract traveling waves, physical phenomena in which electrical activity propagates across the brain like ripples in a pond. The scientists then analyzed these signals in simulations with transfer entropy, a mathematical metric that quantifies the directional flow of information. This approach allowed the team to investigate how tightly the neural signals and informational flows are linked.

Simulation results revealed that the mere presence of traveling waves and their propagation does not guarantee information transfer. However, the scientists confirmed that information in the cerebral cortex flows selectively along the propagation direction of the traveling waves, a phenomenon they call informational tuning. They observed that the resulting curves of this tuning are significantly sharper during wakefulness as compared to anesthesia. On the other hand, the researchers were intrigued to find that the absolute amount of transfer entropy was actually higher during anesthesia than in wakefulness.

"This unexpected finding suggests that while the anesthetized brain is flooded with random, noisy information, the awake brain selectively regulates information in specific directions," says corresponding author Yutaka Komura. "In other words, the awake brain excels in the 'reliability' and precision of information communication, rather than just the raw quantity."

By marrying the biological reality of traveling waves with the mathematical rigor of transfer entropy, this study demonstrates how the waking brain efficiently sharpens its internal communication to ensure reliable information flow, and provides a quantitative metric to evaluate the efficiency of information transmission between cortical regions.

But there is much more to uncover.

"Our future goal is to bridge the gap between our findings on informational tuning and deeper neural circuit mechanisms," says Komura.