Dr Emery Neal Brown, 54, is a professor of anaesthesia at Harvard Medical School. He has published more than 150 scholarly papers and recently, in a paper in the New England Journal of Medicine, he outlined the differences between general anaesthesia, sleep and coma. He continues to practise at Massachusetts General Hospital, and is also a professor of computational neuroscience and health sciences and technology at MIT, where he works on developing statistical methods for neuroscience analysis.

Tell me about your research.

Since 2004 we have been doing experiments on animals and humans to understand how the brain works under anaesthesia. So we record the EEGs [brain waves] of patients who are having general anaesthesia, or volunteer subjects, to see and understand what happens in the brain.

And what have you found out?

The main thing is that general anaesthesia is not just about the brain being turned off. Certain parts of the brain are turned off, but in other parts transmission becomes noisier, and in some parts transmission becomes hypersynchronised. All those things can help you be unconscious.

If the brain is turned off, it is easy to understand why a person is unconscious, and that is typical when someone is in a stroke. But have you ever seen someone having a seizure? They are conscious, they lose consciousness as the seizure starts, they come back. If you look at the brain it is highly active in a very synchronous way, and this hypersynchronous state can make a person lose consciousness. It is like having a loud hum down your phone line – you can't communicate.

We've also found many aspects of an EEG of anaesthesia are really consistent with patients who are in a coma. The key difference is that anaesthesia is reversible.

You say a brain under general anaesthesia more closely resembles a brain in coma than asleep. Is the distinction clear?

Your brain is in a completely different state in sleep compared with being in a coma or general anaesthesia, and the differences are not subtle. It is apples and oranges.

Think about it. If you are deeply asleep, I can eventually shake you awake. In a state of general anaesthesia that won't happen.

Surgery is invasive and traumatic and you need to be in a state that is like a coma to tolerate it. General anaesthesia goes beyond simply controlling pain. It has four components. You are supposed to be unconscious. You are not supposed to remember – having open heart surgery is not an experience you want to remember. Third you must not feel pain and fourth you should not be about to move about. Plus you need to be physiologically stable: heart rate, lungs, blood flow, and body temperature.

And yet we still talk about putting people to sleep…

If you came in for an operation and I told you I was going to put you into a coma, you would probably get up and run away! The idea of being put to sleep is a euphemism. But I think it is important to be honest. We need to educate the public more. For your surgery you need to be in a state of general anaesthesia, not sleep, for the reasons above – I can put you in, I can bring you out.

Before your research, is it true to say that there was little enquiry into how anaesthesia worked? Practitioners were just satisfied that it did work…

I think that attitude is pervasive in our field. There were people looking at how anaesthetics work, but what is different about our work is that we are explicitly saying you have to use neuroscience to do it. What has led research in the past has been pharmacology and receptors [drug binding sites] – to describe how the drugs work. But if the bulk of the effect of the drugs is in the brain and the nervous system, you have to ask what parts of the brain they are working in. Because you can have the same receptor in one area that causes an excitatory effect that in another causes an inhibitory effect.

So do you see anaesthesiology becoming a branch of neuroscience?

Absolutely. It already is! Probably nobody manipulates the brain more than anaesthesiologists. In the US, between 60,000 and 90,000 patients have general anaesthesia daily. That is a lot of expertise accruing about brain neuroscience.

What is the potential of your research?

The possibilities are limitless. Insomnia is a big problem, for example. A lot of insomnia drugs work like low doses of anaesthetic drugs – they create sedation, not sleep. The goal of treating insomnia is to promote natural sleep, but sleep is a cycle, as your brain moves between REM and non-REM sleep, and it can be very active. How can one drug induce a cycle? That is why people who take a sedative may wake up and still feel groggy. They haven't been through the natural stages of sleep necessary for the body to recover. If we work from what we now know – that anaesthesia isn't sleep – then we can help.

Can you explain stories of people being aware under anaesthetic?

These are horrible cases and usually occur in emergency, medically complex situations. But it is avoidable. If certain patterns are visible on the EEG, I can feel 100% sure that you're not going to be aware.

Can you do the same – in reverse – for someone in a coma and see whether they are aware?

Yes, and this is an active area of research by others. We are realising that our ability to communicate with someone in a "coma" may only be limited by our ability to understand how they can respond. So let's say someone was a tennis player, and we know that tennis players, when they think about a serve, activate a particular part of their brain. You say to the person, "If you are hearing me, pretend you are doing a tennis serve", and you see the person activate that area of their brain. They are not locked in. If you know how to communicate with them, they can respond.