A groundbreaking metric reveals how our brains shift between states of awareness and unresponsiveness during sleep and anesthesia

Ever wondered what happens in your brain when you drift off to sleep or go under anesthesia? A new University of Michigan study has just unlocked key secrets behind how our brains switch between consciousness and unconsciousness.

A recent study published in Nature Communications by Hyunwoo Jang, George A. Mashour, Anthony G. Hudetz, and Zirui Huang from the University of Michigan reveals insights into how brain networks shift between consciousness and unconsciousness during sleep and anesthesia.

The research introduces a metric called the Integration-Segregation Difference (ISD), which assesses how effectively brain regions communicate with one another (integration) versus how distinct they are from each other (segregation). Understanding this balance is crucial, as consciousness depends on a precise interplay between these two dynamics.

The ISD was developed to measure and predict transitions in brain states, such as from wakefulness to deep anesthesia induced by the sedative propofol, as well as through natural sleep cycles. “Our findings show that when we lose consciousness, brain networks tend to isolate rather than cooperate, and this segregation increases as we drift further into sleep or under anesthesia,” the authors noted.

To evaluate changes in consciousness, the team used functional magnetic resonance imaging (fMRI) to monitor brain activity. They applied ISD to examine shifts in brain connectivity as subjects transitioned from wakefulness to anesthesia-induced unconsciousness. The study found that when consciousness fades, the ISD shifts toward segregation, with brain regions operating more independently and less communication occurring across the network.

Additionally, the researchers applied machine learning to analyze ISD changes and accurately identify awake and unconscious states. This analysis provided a deeper look into brain states, identifying unique patterns in brain activity. They also analyzed “metastability” (a brain’s ability to switch between different states) and complexity (diversity in neural patterns), which are closely linked to integration and segregation.

This study has significant implications for understanding consciousness disorders, sleep dynamics, and the effects of anesthesia. It opens up potential future applications for using ISD in clinical settings, providing a new tool for assessing the states of individuals who cannot communicate their level of consciousness. “By monitoring ISD, we could have a powerful way of assessing brain function in patients who are sedated or in states of impaired consciousness,” said the researchers.

The complete study can be found at https://www.nature.com/articles/s41467-024-53299-x#citeas

Study Accreditation: Jang, H., Mashour, G.A., Hudetz, A.G., & Huang, Z. (2024). Measuring the dynamic balance of integration and segregation underlying consciousness, anesthesia, and sleep in humans. Nature Communications, 15(9164).