NEUROSCIENCE

Intro: A new research study helps to measure levels of consciousness

“OUR brains produce more entropy when we are awake than when we are asleep.” The finding from a research study could lead to better ways to measure the consciousness of people who appear to be in a coma.

Entropy is a measure of disorder, and in our universe, everything tends to move from less disorder to more over time. For instance, breaking a coffee cup increases entropy. While this breaking can happen in many ways, you never see a broken cup spontaneously reassemble itself and therefore decrease its entropy.

Electrical signals in our brains can also produce entropy as part of processing and transmitting information, such as the visual signals from our eyes. Researchers at the Paris-Saclay University in France wanted to determine whether our brains produce more entropy when we are awake or when we are asleep.

The scientists used functional magnetic resonance imaging (fMRI) to scan the brains of 15 people in different states of consciousness: while each person was awake and in three stages of sleep, from light to very deep.

To calculate entropy, the research team used a model that was previously developed from studying the pathways that electrical signals can follow inside of the brain. The different routes help reveal the different processes they can carry out, and each of those processes produces different amounts of entropy. From this, the researchers calculated entropy production for each person in each state of consciousness. The findings suggest that entropy decreases as people fall deeper into sleep. In the state of deepest sleep, people’s brains, on average, produced 25 per cent less entropy than when they were awake.

This now gives researchers and scientists a way to quantify consciousness. A person whose brain shows the same amount of entropy production in an fMRI study as someone who is deeply asleep is likely to have the same types of processes happening in their brain and to be at a similar level of consciousness.

This new method could potentially be used to quantify the consciousness of people in comas or eventually help to diagnose people with locked-in syndrome, who are conscious but unable to communicate with the external world.

Previous research has linked consciousness to entropy. Some fMRI studies, for example, have indicated that states of very altered consciousness, such as those induced by psychedelic substances like psilocybin, result in an increase in entropy of the brain itself – meaning that it is harder to predict its overall electrical state – and not just the entropy different signals produce.

Understanding the state of awareness of people that are minimally conscious has long been an area of scientific study. However, it isn’t yet clear that entropy production is an unambiguous mark of consciousness.

For example, dreams can happen in deep sleep – a time of low entropy – but they reflect a high level of consciousness. As such, dreams could actually increase entropy production in the brain, but the study carried out by researchers didn’t consider this.