Not time to wake up (Image: Universal Images Group/Getty)

It’s the day of your operation. As the anaesthetic kicks in, you start to drift off… only to reawaken with a scalpel cutting away at you. It is the stuff of nightmares, and there is no fail-safe way to stop it happening, says anaesthesiologist Alex Proekt, at Weill Cornell Medical College in New York.

People wake under general anaesthetic about once in every 19,000 cases, according to a large study last year, and when paralysing drugs have been used, their awake state can go unnoticed. But that might be about to change. There is mounting evidence that the stability of brain activity could indicate when a person is no longer still under, and enable us to do something about it.


Proekt and his team used grids of electrodes placed directly on the brain to record the activity of four monkeys as they lost consciousness under one of two common anaesthetics. They then used computer modelling based on dynamical systems theory to test how stable this activity was.

According to this theory, stable systems can respond to changes by returning to a baseline state, whereas unstable systems go haywire. While awake, the monkey brains seem poised between mathematical stability and instability. But as the monkeys succumbed to anaesthesia, the activity of their brains became more stable.

A study in April found that tiny bursts of stability, in which brain activity holds steady for hundreds of milliseconds, are necessary for us to consciously perceive something. But Proekt’s work suggests that if this goes on for too long, you will become unconscious. Conversely, modelling suggests that if signals spread too much, this may also cause a loss of consciousness. “The brain is somehow balancing between the two,” says Proekt.

Together, the studies illustrate the delicate balance of the conscious brain, says Aaron Schurger of the Swiss Federal Institute of Technology in Lausanne, who did the earlier work. “The system is pushed towards the boundary between stability and instability so that it can perform a delicate dance from one state to another,” he says.

Doctors can currently use methods like EEG monitoring of brain activity to check whether a patient is still unconscious. But the signals that these monitors pick up vary with the depth of anaesthesia, and don’t work for certain drugs. By EEG measures, the brain of someone knocked out with ketamine looks the same as that of an awake person.

Proekt thinks being able to record and test the stability of brain activity in real time will allow him, and other anaesthetists, to more accurately assess the consciousness of the people they are putting to sleep and keep them under for the required length of time.

Journal reference: Journal of Neuroscience, DOI: 10.1523/jneurosci.4895-14.2015