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Lights aren’t on but is anyone home? Detecting awareness in coma patients

Awareness can be detected in people previously thought to be in a permanent vegetative state using a cheap, portable electroencephalography (EEG) device, according to a study published in today’s Lancet…

A new study shows EEGs can detect consciousness in those thought to be in a vegetative state. Flickr/Basheem

Awareness can be detected in people previously thought to be in a permanent vegetative state using a cheap, portable electroencephalography (EEG) device, according to a study published in today’s Lancet.

British and Canadian authors assessed 16 patients in a vegetative state, along with 12 healthy controls. Three of the 16 patients who were thought to be unconscious could repeatedly and reliably generate appropriate EEG responses to two distinct commands, despite being physically unresponsive.

Ashley Craig, Professor of Rehabilitation Studies from the University of Sydney, explains how consciousness is currently tested in people thought to be in a vegetative state, and how that might be about to change:

We’ve known for some time that when someone appears to be in a coma, they may actually be conscious. The trouble is, this is incredibly difficult to assess.

This type of research has been going on for some time. Past studies have shown, for instance, that people in comas have similar heart rate responses to music to conscious people.

How is consciousness currently determined?

Very few hospitals would provide an EEG system and there are many limitations to fMRI scans, so most diagnoses would be based on behavioural observations. In the acute ward, clinicians would observe vital functions such as heart rate, respiration, and responses to commands and questions. If there’s no response, then it might be assumed the patient is in a coma.

What are the implications of this assumption?

It could be that families are asked to turn off vital supports. Or the patient might just be ignored. They might be left in a home where there’s no effort made to talk or communicate with them.

One of the recommendations in this paper is that EEG technology could be capable of communicating with people in a semi-vegetative state, where they are conscious but are hard to get to.

A patient wearing electrodes for an EEG. Aschoeke

How would this work?

It’s not dissimilar to what we’ve been doing with Mind Switch, which uses brain signals to allow people with severe disabilities (without the use of their limbs) to use their mind to turn technological devices on and off.

We target waveforms in the brain that respond to things such as closing and shutting the eyes or imagining movement. These waveforms increase and decrease with these actions or thoughts, which can then be used as a hands-free switch or communication tool to show activity. We’ve been publishing in this area for some time.

In today’s study, the authors asked the patients a question and told them to do or think about something, such as playing tennis. They found that some of those people who were supposedly in a coma reacted similarly to the able-bodied or the non-injured people in the controls group.

The researchers are saying that something like Mind Switch could be used to communicate with people who are aware but are in a vegetative state.

What proportion of people in a semi-vegetative state would be able to communicate?

I’m not aware of any data but the researchers detected consciousness in three out of 16 participants. It’s a very small sample, but these cases come up from time to time.

A man in Sweden was assumed to be in a coma for most of his life until EEG tests were undertaken. It turned out he wasn’t in a coma – he was conscious. For 30 or 40 years, he was confined to a room where nobody talked or communicated with him, then they realised he was there.

If we had better forms of detecting awareness such as EEG technology – which is perfect for this – we may not make these mistakes.

I don’t think many people would fall into this category. But if it’s two out of 50, it’s worth undertaking these tests.

Why isn’t EEG used more often to detect awareness in people thought to be unconscious?

It’s not hard to attach a few electrodes to someone’s brain. But you need very specific skills to be able to detect activity. EEG is a science, of course, but it’s also an art form. You’re trying to detect brain activity that’s an incredibly small amount of voltage.

If you think about the heart beat, it’s about a thousandth of a volt. Activity in the brain is a millionth of a volt. Clearly, brainwave activity can be swamped by other things such as muscle (which is a thousandth of a volt) and heart rate, which can give false readings.

Sometimes people look at EEGs and think they’re seeing something but really they’re only seeing an artefact: for example, if I blink my eyes you’ll see that recorded in the EEG but it’s not an EEG signal, it’s an artefact signal rising from the eye blink.

In our EEG studies, we use sophisticated artefact removal techniques in order to see the real signal.

So EEG is probably not very commonly used because there are those sorts of barriers or limitations. They may be cheap to buy but they’re expensive to operate.

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4 Comments sorted by

  1. Nathan Stewart


    Would this also apply to people that are thought to be brain dead? You always seem to hear stories of people about to have their life support turned off before the person wakes up at the last minute....

    1. Ashley Craig

      Professor of Rehabilitation Studies at University of Sydney

      In reply to Nathan Stewart

      Sorry for the delay in replying. Brain dead is usually applied to someone who is has irreversible damage to the brain, in which all brain activity (including involuntary activity necessary to sustain life) is absent. This is very different to people in a supposed vegetative state. Death is determined by the lack of bodily functions such as respiration and heartbeat. However, medical teams can resuscitate people with no respiration and heartbeat, or other obvious signs of life (within a short time window of course), so a need for improved definitions of death is clear, especially when life support can maintain body functions indefinitely

  2. Pamela Snow

    Associate Professor of Psychology at Monash University

    This line of research is important, at both theoretical and clinical levels, but it must be remembered that "signs of awareness" does not equate with being cognitively intact but "locked in" - which is the dichotomous way in which the media tends to portray impaired consciousness after brain injury. It's also important to note that injury aetiology is important in determining clinical course - a traumatic brain injury is very different in terms of underlying pathophysiology (and natural history) than for example, a vascular lesion or a postencephalitic state.

    In response to the query above - no- brain death is a distinct entity and can be determined conclusively on the basis of well-accepted clinical measures.

  3. Shane Riley

    Coma Victim/Survivor

    This may not be the correct place to ask, but I have just recently come out of a Coma which I am told was self-induced if this is at all possible. Test were done and all information point to no viral or physical problems. So why did I go into a Coma?
    I was found on the floor at home what appeared to be a seizure, then I went into a Coma. Paramedics rushed me to hospital where I remained in a Coma for several days. I recalled, whilst in this state of a sensation of choking and not being able to breathe, then falling back into the darkness where I was at ease. I have no memory of where I was not the events of the day. My family later told me that I had responded to my wife's voice and went into another seizure, before slipping back into the Coma.
    I understand that this may not be the best place to ask, but I have many questions. Is there somewhere I obtain answers to this area?