Anesthesia May Leave Patients Conscious—and Finally Show Consciousness in the Brain

By Vaughan Bell | January 4, 2012 8:46 am

Vaughan Bell is a clinical and research psychologist based at the Institute of Psychiatry, King’s College London and currently working in Colombia. He’s also working on a book about hallucinations due to be out in 2013.

During surgery, a patient awakes but is unable to move. She sees people dressed in green who talk in strange slowed-down voices. There seem to be tombstones nearby and she assumes she is at her own funeral. Slipping back into oblivion, she awakes later in her hospital bed, troubled by her frightening experiences.

These are genuine memories from a patient who regained awareness during an operation. Her experiences are clearly a distorted version of reality but crucially, none of the medical team was able to tell she was conscious.

This is because medical tests for consciousness are based on your behavior. Essentially, someone talks to you or prods you, and if you don’t respond, you’re assumed to be out cold. Consciousness, however, is not defined as a behavioral response but as a mental experience. If I were completely paralyzed, I could still be conscious and I could still experience the world, even if I was unable to communicate this to anyone else.

This is obviously a pressing medical problem. Doctors don’t want people to regain awareness during surgery because the experiences may be frightening and even traumatic. But on a purely scientific level, these fine-grained alterations in our awareness may help us understand the neural basis of consciousness. If we could understand how these drugs alter the brain and could see when people flicker into consciousness, we could perhaps understand what circuits are important for consciousness itself. Unfortunately, surgical anesthesia is not an ideal way of testing this because several drugs are often used at once and some can affect memory, meaning that the patient could become conscious during surgery but not remember it afterwards, making it difficult to do reliable retrospective comparisons between brain function and awareness.

An attempt to solve this problem was behind an attention-grabbing new study, led by Valdas Noreika from the University of Turku in Finland, that investigated the extent to which common surgical anesthetics can leave us behaviorally unresponsive but subjectively conscious.

Rather than researching patients undergoing surgery, they asked for healthy volunteers to be “put under” specifically for the purposes of investigating consciousness during anesthesia. The researchers recruited 40 healthy student volunteers and anesthetized each of them using one of four common drugs (dexmedetomidinepropofolsevoflurane, or xenon) while recording a simple electrical brain response called the bispectral index, which is commonly used as a rough “depth of anesthesia” measure.

In addition to the standard surgical way of checking unconsciousness, participants were also regularly asked to open their eyes to check when they stopped and started responding. Afterwards, each participant was questioned about their memories of the anesthesia session to see if they had conscious experiences even when seeming to be comatose. These included simple thoughts or perceptual experiences like flashes of light, to more complex experiences such as seeing or hearing the researchers, or having dream-like, out-of-body hallucinations.

It turns out that despite being rated as unresponsive and, therefore, by the current medical definition, unconscious, participants reported conscious experiences in about 60% of the sessions. This does not mean that everyone was “awake” as we normally understand it, as the extent to which the experiences reflected the reality of what was going on around the person varied, but the volunteers were clearly having conscious experiences.

“I had a dream in which one of the nurses here got suspended from her work, which was not a bad thing after all”, and then “I saw a beautiful beach”

“I had a dream in which my friend’s roommate, who studies medicine, was sitting next to me here in the laboratory, telling me that we have to go to the city”. “At some point I was a bit anxious, but after that I felt extraordinarily good”

Had several quick visual experiences. In one vision the participant was “playing football”. “Suddenly [after the football dream] we were pirates, and at some point we went to swim”, “when the drug started to work, my head came out of my body”

It’s important to note that although consciousness was reported in about 60% of the sessions, this isn’t a good guide to how frequently this happens in actual surgery. Surgical operations typically use much higher levels of anesthesia and research suggests that awareness during surgery happens in about 1 in 1,000 cases and is typically fleeting. In fact, in this study, the researchers tested a selection of anesthetics but only used one in each session, whereas surgery typically involves several drugs at once.

Nevertheless, the finding that common anesthetics, when used alone, may leave us unresponsive but conscious is fascinating in itself. Moreover, the study is perhaps more important for pioneering a technique that may help us understand how consciousness relates to brain function. The team suggest that slowly increasing levels of anesthetic in experimental studies could help us pin down exactly which neural changes are linked to the disappearance of subjective experiences—like a dimmer switch for the conscious mind that can be used alongside brain scanning and neuropsychological experiments.

Testing various drugs may help: this new study found tantalizing evidence that different anesthetics affect the ability to respond and have mental experiences at different depths of sedation, in line with the fact that they are known to have radically different neurochemical effects. So in addition to being an essential medical tool, this technique may also help us dissect one of the greatest hard problems of cognitive science.

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  • Techs

    One of the times I was in surgery I woke up in the hall on the guerney for a short period of time and then went back to sleep. In the operating room I woke up fully and could feel my bones vibrate as they pounded on my ankle and leg bones trying to get them back together. No pain or any other sensation. Great look on the surgeons face as he noticed me watching him. He waved to someone behind me and I went back to sleep.

  • Orwin O’Dowd

    Given that no pain has been reported, researchers should certainly pause hee to consider the function of dreams. Hippocrates found them of diagnostic interest, hence responding to change in the body, which certainly happens during surgery. Don’t swamp natural self-regulation without checking the facts! No don’t!!

  • Neuroskeptic

    Interesting study but it’s hard to know whether the reported dreams actually occured during the anaesthesia as opposed to when they were just waking up from it.

    Subjectively it would seem the same because you’d remember dreams before you woke up, you might interpret that as being during the depths of the anaesthesia, even if it was only 5 minutes before you awoke.

    Similar to how, unless you wake up in the night & look at the clock, it’s often impossible to tell when you had a certain dream. most dreams happen during the later part of the night (when REM sleep occurs) but it seems like they happen “as soon as you go to sleep” because of course you’re not conscious of the time between when you go to sleep and when the dream starts…

    The way to find out, I think, would be to present stimuli during the anaesthesia and see if they make their way into the dream.

    e.g. everyone knows how if you hear your alarm clock, sometimes you dream about an alarm. Or if you’re thirsty you dream you are thirsty.

    The problem is it doesn’t always happen so you would need a very large sample size.

  • Neurobonkers

    Nice post, where’s the link to Vaughan’s AMAZING Mindhacks blog?

    Arguably the best neuroscience blog on the web!

  • Pingback: Gadgets, Brains, and Healthcare « boydfuturist()

  • The Corresponder

    A greater knowledge of consciousness will hopefully impact the current treatment of comatose patients who are supposedly in a “vegetative state” and some people’s eagerness to take them off life-support.

  • David Turell

    This is a skin-deep article. This type of reasearch will not lead to an understanding of consciousness.Where consciousness becomes a fascinating problem is in all the reports of near-to-death episodes, with flat line EEG and EKG and the patient reports episodes with figures from the ‘other side’ delivering ‘new’ information the patient did not receive in any other way.

  • Gaspasser

    As a study looking at consciousness and brain function, it may be of some value. However I think the title uses a bit of sensationalism – Anesthesia leaves patients conscious? At least in the article the frequency and poor correlation to anesthesia in surgery is explained fairly well.

  • Doctor Watchdog

    I wonder whether there is a connection to this and women patients who report being molested by their anesthesiologists. Many such reports have been dismissed as hallucinations induced by the anesthesia. Given that the “hallucinations” seem to almost exclusively to happen to women patients, and given that periods of consciousness do occur with anesthesia, perhaps these women are not experiencing hallucinations after all?

  • castor pollux

    I had a surgery to remove an epidermoid tumor from my spine when i was young. Though i had been “put under” i can vividly remember the doctors conversing above me for quit a while. I also remember feeling heavy pressure at the site if removal, which apparently was me being cut open. This being said, i feel this study is quite important my experience has, in turn, caused an eternal fear of going under the knife in the future.
    I hope this study helps other patients experiences be a little more dream-like.

  • Roger

    My own experience is completely different. Anesthesia was like being turned off. There was no sense of anything. One second you’re counting backwards from 100, and the next you’re in the recovery room.

  • Veda

    As just after a minor surgery i woke up with a recollection that ‘I heard a longish bell ringing, which gradually faded… and felt that all the docs had goneawaay leavimg me alone on the table and that I have had to scream out for HELP’ ….I recounted this to the nurse and asked her if any unusual thing happened….

    WEll she tokd me that the anaesthesia in the cylinder which they thought would suffuce for the purpose was not enough .. and that I woke up[ halfway through and gave a kick..towards the doc… and the bell did ring… as I was connected on to a new cylinder !!!!!

  • Victor Grauer

    One of my oldest “dreams” was also the most vivid and memorable. Though I can’t be sure, I have a feeling it was based on my experiences as a young boy while having my tonsils out. I remember I was given ether and still remember very clearly having a mask put over my mouth and nose and being asked to count. The “dream” involved my being magically transported to the top of a pyramid, controlled by a group of “Indians.” One of them took out a knife and stabbed me. I “saw” concentric circles emanating from the pyramid, very much like radio waves.

    Many years later it occurred to me that the events of my “dream” could have taken place prior to and during surgery. For example, being transported to the top of the pyramid could have been a memory of being taken to an upper floor in an elevator, and the “Indian” with the knife could have been the surgeon.

    This “dream” was absolutely unique, totally different from any other I’ve ever had and it’s stayed with me all my life. It was very very weird, and somewhat upsetting, but not totally unpleasant and I don’t recall being in any pain. Afterward I had ice cream and everyone made a big fuss over me, so all in all it wasn’t too bad. But this “dream” haunted me throughout my childhood. I wonder if anyone else has had a similar experience.

  • Old Bill

    Had prostate surgery 9 yrs ago. Was worried I would wake up during the operation. But like Roger poster #12 went out then woke up in recovery room. But was still afraid even after the operation.

  • George Jochnowitz

    The most horrible experience of my life took place when I woke up after surgery unable to try to move. I wasn’t breathing and couldn’t feel the air being pumped into my mouth. Here is the story in greater detail:

  • Zach

    when I had my wisdom teeth removed they had a bit of difficulty putting me under (back then I had been abusing opiates) after the third try I seemed to be asleep but I remember a large portion of the procedure. I recall them removing the teeth though to me it felt like they were cracking them inside my mouth, at some point they realized I was conscious because they told me that they just had to “stitch you up and then it will be over.” my last memory is of one of the people in there sling shooting his rubber glove into a pan across the room and chuckling, I think he said “watch this.” It should be noted that at this point in my life I had a serious tolerance for a variety of pharmaceuticals but they didn’t seem to terribly surprised that I was trying to talk to them during the last part of the procedure.

  • SocraticGadfly

    The phrase “subjectively conscious” is a bit of an eyebrow squinter, especially since the piece started with the idea of portraying consciousness objectively.


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