May 29, 2002

Consciousness under anesthesia

SCR Feature, neuroscience — thomasr


A breakthrough in testing unconsciousness during anesthesia

So you thought that research in consciousness did not have any practical applications? Now, researchers are monitoring your level of consciousness during deep anesthesia. Imagine that you are anesthesized before a surgical operation. You would probably expect to “black out,” and then wake up some time afterward. What then if you suddenly found yourself conscious of the surgeon’s knife – during the operation? Even worse, you might not be able to let anyone know you are aware.

In 1979 a “medically qualified lady” wrote an editorial called On Being Aware in the British Journal of Anesthesia, describing her own experience of waking up in the middle of a Caesarean section - an incision of her abdomen “…it was followed by the pain - as suddenly as though I had been stabbed” to facilitate giving birth. “I went unconscious very suddenly,” she wrote, “literally as though someone had switched the lights out. After a gap of uncertain time I gradualy became aware of a mental haze in front of me. I was profoundly confused. This relatively happy state was interrupted by a voice in the space above me (some remark about my bladder) and I instantly understood my predicament: that I was lying there, covered in green towels, my abdomen split open … Immediately following this there came three rough stripes across my abdomen. Almost before the third stripe was finished, it was followed by the pain - as suddenly as though I had been stabbed. It was bad from the onset, and it increased in severity. The nearest comparison would be the pain of a tooth drilled without local anesthetic - when the drill hits a nerve. Multiply this pain … and then pour a steady stream of molten lead into it. …”

An estimated 40,000 to 200,000 mid-operative awakenings may occur each year in the United States alone. Medical science has been aware of the problem for many years, but it is maddeningly difficult to solve. Anesthetics are toxic at higher dosages; give too much, and patients may stop breathing; give too little, and they may feel pain. Anesthesiologists must walk a fine line, and so far there has been no objective way to measure “depth of unconsciousness” to give accurate guidance.

Now, in two upcoming articles, E.R. John and co-authors present the scientific basis of a “Consciousness Monitor,” designed to yield a single In the US alone, between 40.000 and 200.000 experience mid-operatrional awakenings every year measure of depth of anesthesia. The US government has approved John’s Consciousness Monitor - called the Patient State Analyzer - for surgical use. The Consciousness Monitor is based on standard EEG (the brain electrical activity measured by electrodes on the scalp), which all hospitals use. It is built into a computer program that performs a quantitative analysis of the EEG from moment to moment. Early results are encouraging. If the Consciousness Monitor works, it may prevent thousands of cases of agonizing pain in the midst of surgery.

The fundamental science underlying the new technology is important. E.R. John and his team found a marked drop in the gamma-band activity (25-50 Hz) during anesthesia, a range of brain waves that is often associated with consciousness. As soon as patients lost consciousness they showed an increase in slower waveforms, a great increase in EEG power and synchrony over the front of the brain, and a loss of coordination between the major regions of the cortex. All the observed changes were reversed when the patients regained consciousness.

These findings are in line with long-standing observations about EEG in Unconscious states generally show slow, high-voltage and coherent waveforms unconscious states like deep sleep and general anesthesia. Unconscious states generally show slow, high-voltage and coherent waveforms, very different from conscious states like waking and dreaming. Slow and coherent waves imply that little information is being passed between neurons; they are all singing the same song. In contrast, irregular electrical waves during waking and dreaming suggest continuous chattering of billions of neurons to each other. Information is then being passed back and forth at great speed and complexity.

Consciousness is often thought of as an integrative activity of the nervous system. Large-scale information transmission among groups of neurons is presumably required for integration, and it makes sense that a loss of consciousness will block this process.

In general, John et al suggests that anesthetics may work by inhibiting the cooperation between the thalamus - the way-station to the cortex - and the cortex itself. This idea is consistent with the widespread hypothesis that consciousness depends upon reentrant activity in the thalamocortical core of the brain.

What makes this work ingenious is the gathering of data into a coherent model, and the bold idea of a device that can measure patients’ conscious state. If the Consciousness Monitor should prove a success, it will have many uses. Patients going into surgery will have more confidence about being protected from pain awakenings; surgeons and anesthesiologists will benefit as well. And the Consciousness Monitor could have scientific uses as well - i.e. to study levels of consciousness.

The broad outlines of EEG in sleep and waking have been known for 70 years, ever since Hans Berger first noticed obvious differences in gross electrical brain activity when people woke up to consciousness and fell asleep. Today we may be coming closer to a real understanding of this fundamental fact.


  1. Anonymous (1979) Editorial: On being aware. British Journal of Anesthesiology, 51, 711-712.
  2. Baars, B.J. (2001) Editorial: The Brain Basis of a “Consciousness Monitor”: Scientific and Medical Signifance. Consciousness and Cognition, 10, 2, 159-164.
  3. John, E.R., Easton, P. & Isenhart, R. (1997). Consciousness and cognition may be mediated by multiple independent coherent ensembles. Consciousness & Cognition, 6 (1), 3-39.
  4. Steriade, M., D.A. McCormick, R.J. Sejnowski (1993). Thalamocortical oscillations in the sleeping and aroused brain. Science, 262, 679-685.
  5. Tunstall, M.E. (1980) - On being aware by request. A mother’s unplanned request during the course of a Caesarean section under general anaesthesia. British Journal of Anaesthesia, Vol 52, Issue 10 1049-1051.


  1. I found this artiacle very interesting since I experienced “consciousness” during my caesariansurgical intervention, fortunately not in the same way as the lady did. In fact I heard the doctor talking, making jokes,. I was unable to talk and I wanted to lift my hand so that after the operation I could tell him that when I was lifting my hand I wanted to let him know that i was hearing him but I could not. I was in a peaceful state, drifting into a channel but when he ws stitching me, it was a bit painful. When he came to visit me after the delivery, I asked hime about his jokes, he was a bit embarased, fortuntaely it was not bad jokes.

    Comment by Francoise — January 28, 2007

  2. When we are able to detect and specify those neurons that the anesthetic dose missed to anesthetize then the “consciousness Monitor” would prove a breakthrough and may bring us closer to that real fundamental fact about the brain activity of waking up to consciousness and falling asleep. Anyway, it is, even as is, quite promising, yet the field test would tell us more about its practical benefits.

    The self watches “the consciously perceived scene” exactly the way it does at near-death experiences: It remains inside,yet overlooking the inside as well as the outside. The onlooker ‘Self’ abandons the body completely if the ‘Immortal Soul’ abandons the body first. Only then the Self abandons the body ‘following’ and never ‘preceding’ the ‘Soul’ that have decided to leave the collapsed/broken/detoriorated/too diseased (body) house, the one where it can no longer find proper dwelling. The pain felt by the woman during the Caesarean surgery is due to the Self’s physical component.

    Comment by Abdu "The One" — April 7, 2007

  3. I believe I may be a person on whom general anesthesia would not work. Injected dental anesthetics (several instances) simply do not affect me, nor did one instance of an injected local anesthetic. Alcohol does not get me drunk. For what it’s worth, many of my dreams are lucid and I sleepwalk under stress. I am not a scientist and have no idea how consciousness works, but mine seems to work a bit differently than most.

    I could use significant dental work and haven’t had it because the pain is ghastly. I am also concerned that if I should ever need general surgery, the anesthetic wouldn’t affect me.

    Are there any resources for people like me?

    Comment by Jones — May 5, 2007

  4. I was very happy to have found this page and to find that I’m not the only person that anesthesia does not work on. I had liver resection. My doctor remove an adinomea from my liver. I woke up durring the procedure. Although I was able to communicate my awakeness with my surgeon and his team. But there was nothing they could do. I had been given all the anesthesia they could give me. I passed out several times from the pain. Because I had been a victom of a crime prior to the surgery, I had a very bad experience where I thought at first the people in the room were trying to kill me. It was the worse experience I’ve ever had and I know my doctor was scared to death. I was able to move and laying there with my liver exposed and loosing alot of blood trying to fight for my life was the craziest surgery he had ever performed. After screaming his name several times he looked over the headcover and was able to calm me at that time. I then realized that I was under going my liver surgery and just tried to make it through. D.K.Greene

    Comment by DENNA — September 13, 2007