Detecting Consciousness in the Vegetative

People in a vegetative state, usually as a result of brain trauma or anoxia (lack of oxygen) by definition have no signs of conscious awareness or activity. The definition, therefore, is based largely on the absence of evidence for consciousness.

Of course, arguments based upon the absence of evidence are only as compelling as the degree to which evidence has been properly searched for. In recent years technology has advanced to the point that our ability to detect the possible subtle signs of consciousness in those presumed to be vegetative has increased – mainly through functional MRI scans (fMRI) and electroencephalograms (EEGs).

There has been a steady stream of studies demonstrating that a small minority of patients thought to be vegetative actually display some signs of minimal consciousness. The latest such study was recently published in Neuroimage: Clinical by a research team from the University of Cambridge.

But let’s back up a bit first. Even prior to evaluating vegetative patients with fMRI and advanced EEG techniques, several studies showed that a detailed neurological exam specifically designed to detect the most subtle clinical signs of consciousness could find such signs in some patients who were diagnosed as being vegetative by more standard neurological exam. According to one study as many as 41% of patients diagnosed as vegetative were really minimally conscious, meaning they had subtle signs of consciousness, but still cannot wake up, converse, or act purposefully.

Other studies have shown that use of a bedside EEG is a cheap and portable option for properly detecting patients who are minimally conscious rather than vegetative.

Then fMRI began shining an intriguing light into the brains of some of these patients. One early study used fMRI to image the brain activity of an apparently vegetative patient when asked to imagine themselves playing tennis or walking around their home. The researchers were able to show that the patient would demonstrate the appropriate pattern of brain activity (compared to the established baseline) when later asked to repeat the task.

This was a stunning finding, and has later been replicated in other patients. The current study falls into this category. The researcher examined the brains of eight healthy controls while performing the task of listening to a stream of words and counting the number of times the word “yes” or “no” appeared. They then repeated the task with 21 vegetative patients. Of those, 17 showed no brain activity at all, three showed brain activity but it appeared to be random, and one patient displayed brain activity similar to that of the eight healthy controls.

The results of this study suggest that one of the 21 vegetative patients was able to direct their attention at the task in a way that was indistinguishable, by fMRI, from a healthy person.

While extremely interesting, the big question remains – what does all this mean?

The first question we always have to ask is if these results are reliable, or could they be due to an artifact or some error in the protocol. fMRI technology is still very tricky to use, and notoriously produces false positive results when not used carefully.

The results have been replicated enough, however, that at least they should be taken very seriously. There is also another reason to accept the results are probably real. One interesting pattern that has been fairly consistent in the research is that those in a vegetative state from trauma are more likely to demonstrate signs of consciousness than those resulting from anoxia.

This makes sense in that anoxia damages the entire brain, and such diffuse injury does not leave much potential for residual brain activity. Brain trauma, however, can be very non-uniform. There may be parts of the brain relatively spared and still able to participate in consciousness. Further, trauma may cause focal damage resulting in paralysis or sensory impairment that hides signs of consciousness.

Assuming, therefore, that the results are real, what are the implications? From a theoretical point of view, what we want to know is – what is happening inside the mind of those people who appear vegetative but have fMRI activity in these studies? This is the one thing we really want to know, but just can’t at this time.

The fact that the brain is showing activity in response to environmental stimuli, even abstract stimuli such as instructions to pay attention or imagine oneself playing tennis, does not mean that the person is experiencing that activity. We still may only be witnessing some component of attention or information processing without the brain being able to generate sufficient activity to produce anything that can reasonably be considered consciousness.

This is, in fact, what I strongly suspect. Further I believe this is a reasonable default assumption lacking compelling evidence to the contrary.

From a practical point of view, what do the results of this research mean? Is there a difference in prognosis or response to treatment for those who display fMRI activity vs. those who do not? The answer so far is probably not and no, respectively.

While it is true that those in a minimally-conscious state have a very small potential to experience modest neurological recovery, while those who are truly in a vegetative state have no possibility of any meaningful recovery, this difference is slight and has practical implications for only the very rare patient.

There are also currently no effective treatments for those who are vegetative or minimally conscious. The hope is, however, that treatments may be developed. In that case, the minority of vegetative patients who do show brain activity may be the ones to benefit from potential future treatments.

One such treatment involves implanting computer chips (or electrodes attached to computer chips) that enhance the activity of the parts of the brain involved in consciousness and wakefulness. fMRI technology may help us identify the minority of patients who could potentially benefit from such a treatment.

Another potential development that is often discussed in news reports of this fMRI research is the use of the technology to communicate with those who are vegetative but have brain activity. I am highly skeptical of this potential, however. It is certainly reasonable to research this to discover what the potential is, but I would recommend extreme caution.

As I stated above, the fact that the brain can respond to stimuli does not necessarily mean that there is a conscious mind present capable of communication. Further, the risk of such research is that non-specific or random responses will be over interpreted as communication – something we have seen with every research program into communicating with those who cannot communicate normally, including animals and those with cognitive impairments.

No such study has been attempted so far, and I am curious to see the protocols and results.


Using advanced EEG and fMRI technology to study the brains of those who appear to be vegetative is an exciting development that promises to teach us something about brain function and consciousness. This research further holds out the promise of identifying patients who may benefit from yet-to-be-developed technology.

At the very least it can reassure families that their loved-ones have been thoroughly examined and properly diagnosed. For those patients who demonstrate no brain activity at all, the family does not have to worry that they are actually locked in, or that they are prematurely abandoning hope for recovery. Proper diagnosis and prognosis is essential when dealing with the comatose, and this technology will greatly enhance the reliability of diagnosis.

Those patients who do show some brain activity despite appearing vegetative are now in a diagnostic gray zone. There is an indication of brain activity, but we just do not know yet what to really make of it. This is truly an area requiring further research.

Posted in: Neuroscience/Mental Health

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34 thoughts on “Detecting Consciousness in the Vegetative

  1. windriven says:

    Fascinating post. It begs the question: what does one do with a patient with minimal but indisputable brain activity? Presuming no chance of recovering meaningful agency, what are the ethics of keeping the patient alive? Of allowing her to die?

    1. goodnightirene says:

      Is vegetative state covered by living wills, or other directives?

      Note: windriven, are you and I the only old people left who say her (or him) instead of “they” when referring to a singular subject? I realize there is a linguistic shift going on before our eyes, but I’m too old (birthday today!) to hear…

      “One early study used fMRI to image the brain activity of an apparently vegetative patient (one person) when asked to imagine themselves (herself) playing tennis or walking around (his) home.”

      …without cringing. I realize we got ourselves into this linguistic mess through women standing up for being linguistically ignored, but it still grates on my old “subject and pronoun must agree” brain. They is still more than one person, but is becoming a substitute singular pronoun. There is a name for this kind of shift in linguistics, but I’ve been out of school too long to remember it.

      1. WilliamLawrenceUtridge says:

        Happy birthday!

        As a proponent of the singular asexual they, I understand the confusion it can generate but still feel it is less clunky to the his/her alternative.

        1. goodnightirene says:

          When did “they” become “singular”? Did I miss that? It wouldn’t surprise me. :-)

          Thank you for the Birthday wishes.

          1. Interrobang says:

            Singular “they” has been around since at least Chaucer. It’s not exactly a new development; it’s just got more currency now because we’re more gender-neutral than we used to be. ( )

            1. Harriet Hall says:

              Thanks! Now that I know more about the history of usage, I won’t have to feel guilty when I write “their.”

      2. windriven says:

        I go back and forth, Irene. I use the s/he sometimes, arbitrarily use he or she, and sometimes use they. My personal preference would probably be a new word (as happened with Ms.) that is a genderless singular personal pronoun.

      3. Carl says:

        I always thought of it as bad grammar for the sake of pointless symbolism. Even after years of the bad language symbolism, old men still say “I don’t want no lady doctor” and Republicans in Texas still want to ban abortions via absurd regulations.

        Dan Dennet seems to hate the bad grammar while still determined to make a social point with language, as he just routinely assumes unknowns to be female.

        I prefer to say whatever I feel like saying at the time, and if anyone actually complains about the word “he” as an unknown then I tell them to get over it and go focus on a real problem. Or maybe I would say that if anyone ever complained.

        1. Harriet Hall says:

          “They” is grammatically wrong and grates, so I try to reword things to avoid using it, but am not always successful.
          “He or she” is clumsy.
          Alternating “he” with “she” would require onerous record-keeping to ensure equal numbers.
          I’d like to go back to using “he” and for everyone to learn that “he” was originally used to refer to a person of either sex. I’d like for women to take back ownership of “he” and “mankind,” and to know that the words applied to them too.

          1. WilliamLawrenceUtridge says:

            I would suggest a Spivak pronoun were it not for the fact that almost nobody would understand it, or you would have to spend days putting in hyperlinks to all your articles.

            1. windriven says:

              Maybe we should adopt Chinese. Ta, the usual third person pronoun, means either he or she. The Chinese, Mandarin speakers at least, don’t give much consideration to gender differences in spoken language.

          2. Lytrigian says:

            And at one time the singular “you”, and using “you” as the subject of a sentence instead of “ye”, were ungrammatical, and I’m sure it grated on many of Shakespeare’s contemporaries. Yet here we are.

            As it happens, it’s not difficult to find old citations of the singular “they”. Look up the Wikipedia article on “Singular they” if you want examples; a professional linguist could provide many more. It’s not an innovation, merely an obscure feature of the language becoming mainstream.

          3. goodnightirene says:

            I enjoyed and appreciate all these replies–good points one and all–but I especially like Harriet’s (may I call you Harriet?–see how old-fashioned I am?*) very sensible solution and the one I have always favored. One tweak on that might be to alternate the presumed “he” or “she” every ten years or so, along with the census, perhaps?

            *Another sign of being hopelessly old is wanting to scream when some twerp barista wants to know your name and then immediately refers to you as “Irene” instead of “Ms. Goodnight” without even saying, “may I call you Irene”!

        2. windriven says:


          I don’t know that Dennett ‘hates’ bad grammar* but I too have noticed that he most always uses ‘she’ for the genderless personal pronoun.

          *I think he only sorta hates it ;-)

  2. Liz says:

    At risk of asking a silly question – can someone please clarify what the difference between being in a vegetative state, and being brain-dead (brain stem death) is? The kind of studies (such as the one above) which show that vegetative patients may experience some awareness tend to be used by those who are a bit queasy about organ-donation, in order to push the “How do we know they’re really dead?!” case.

    1. Brain death = Death. Total loss of brain activity. You may still be good as organ donation source but not for long.

      In vegetative state, the area of the brain responsible for vital functions (breathing, pumping the heart, etc) is still functioning. The other brain functions are impaired, to different extents as Steven discussed above.

  3. windriven says:

    My working definition – and I don’t claim this to be medically accurate – is that brain death means cessation of brain mediated activities like breathing (the heart marches to the beat of its own drummer) while a persistent vegetative state means lack of consciousness and failure to respond to noxious stimuli.

    1. The term braindead is usually used to describe the state in which both brainstem and cortex have lost all function (also called ‘whole brain death’) A vegetative occurs when, after the period of coma (few days to weeks), the patiënt is still not aware but has preserved sleep-wake cycles (1). In Europe the official term is ‘Unresponsive Wakefulness Syndrome (UWS)’.


  4. Brain death requires the complete absence of any signs of any brain activity, including brainstem activity. Patients in a vegetating state can breath, have roving eye movements, can grimace, and can have brainstem reflexes – just no signs that they can perceive or interact with their environment. No signs of consciousness.

  5. Buddha Buck says:

    I will admit to not having read the study in question, but if I understand the summary right, 1 in 20 vegetative patients showed signs of consciousness (p <=0.05). What distinguishes this from green jellybeans correlated with acne?

    1. WilliamLawrenceUtridge says:

      Thats where the interesting part comes in – replication, and attempting to predefine characteristics that allow you to predict who is braindead versus the minimally conscious. One way would be setting up experiments where you test the “global anoxia” versus “specific trauma” – if your minimally conscious percentage rises in the latter, you’ve got a possible distinguishing characteristic.

  6. Carl says:

    1. Mad scientist mode: How about taking healthy subjects and doing the fMRI test during induced comas?

    2. I am slightly unsure if the yes/no test had actually been done. I was under the impression that one of the studies had actually asked the subjects to “think tennis for yes or walking around a house for no” to answer some questions, but the older pages referred to don’t explicitly say so (the wording is something like “shown to be possible”, which is not clear).

    3. If #2 is done, I suggest adding a third option for “uncertain/confused” to see if the patient can recognize questions which are intentionally nonsensical. That could help rule out the possibility that some automated mental process is just latching onto some word. (eg, ask “how fast do tennis rackets walk around houses” and see if they respond by thinking of either walking or tennis, or if they correctly think about cheese to indicate confusion.)

    1. windriven says:


      “How about taking healthy subjects and doing the fMRI test during induced comas?”

      There are a few commenters who appear in these pages from time to time that I would like to recommend as test subjects. ;-)

  7. Vicki says:

    Singular “they” goes back at least to Jane Austen; supposed-to-be-nongendered “he” was legislated in Britain later in the nineteenth century.

    The problem is that you and I might be perfectly happy to say “it says this is open to ‘men,’ and I am an adult human, therefore I am eligible,” a lot of other people have and will argue that “it says ‘men,’ therefore it is for adult males” or even insist that a male child is a man but an adult woman isn’t. I don’t think changing pronouns is going to fix everything, but neither is saying “we want the best man for the job” and then having to explain that this time, “best man” isn’t gendered, the way it would be for a wedding attendant.

    1. Lytrigian says:

      If it came to that sort of thing, I’d be very happy to revert to “man” for human beings, that being a very old Germanic word for our own species. (It’s vaguely ridiculous we must resort to a Latinate polysyllable to talk about ourselves.) It didn’t start to refer to males alone until the 11th century or so.

      In that case, however, we really ought to have a separate word for a male of the species. “Wer” was the old one, now surviving as far as I know only in the compound “werewolf”. I guess that could work. “Wif”, the old word for the female, now means strictly a female spouse (“wife”), but it also contributed the first syllable in “woman”, originally “wif-man” before regular sound-changes removed a consonant and turned the vowel into a schwa. On that model, maybe “werman” for the male?

      1. Carl says:

        Woah. I would totally be OK with people referring to me as a wer-man.

  8. devo-T says:

    Being both a skeptic and a layman with a great deal of medical knowledge, my first reaction was the same as yours (even before I read it): considering the brain functions in ways we don’t fully understand, the results of these tests could be explained by some autonomic feature, not unlike respiration. Having said that, such research should decidedly continue.

    As an aside, the entire concept of PVS scares the living daylights out of me. There are perhaps only two scenarios more disturbing: Locked-In Syndrome, and being declared brain dead when I’m not. Recently, a woman in the US opened her eyes and looked at the doctors just about to harvest her organs, after she was incorrectly determined to be brain dead — despite a number of tests (ice water, plantar reflex, etc) that might avoid this. This happens way more often than you’d think. Dick Teresi’s book, The Undead, goes into some detail about this and the bioethics dilemma that a shortage of organs may force upon hospital staff.

    1. Devo – I don’t buy that story at all. I have read many press accounts of alleged cases, but the details never add up, and the sources are always dubious.

      You’ll have to give me a reference about that US woman.

      The published literature claims there isn’t a single documented case of recovery following a brain-death diagnosis using current criteria.

    2. Liz says:


      I genuinely cannot see how a person can wake up and look at the doctor who is about to remove their organs. For a BD person to become an organ donor, their mechanical ventilation has to be removed and their heartbeat has to cease for an uninterrupted 5 minutes before they can be declared dead (normally this is done with relatives at the bedside). Only after that, can their organs be removed. It would be incredibly difficult for a BD person to then fully regain consciousness at this point, and be annoyed that someone was about to remove their organs.

  9. God says:

    As worthless and subhuman & lying frauds as chiropractors & woo-woo con artists are,
    it’s the free-market capitalist anarchy extremism of medical people to blame.

    The fact is that MDs and nurses have absolutely no-stress jobs.
    They never had to work a day in their lives.
    Nobody who had ANY stress would EVER, EVER, EVER add additionally unnecessary complex paper work to procedures. They would know the costs of procedures
    that they ALLEGEDLY do hundreds of times, BEFORE giving services to a patient.

    They would NEVER EVER work on anyone who votes for conservatives, Republicans, Democrats, christians, muslims, anti-vegans (those who deliberately choose to eat meat even when vegan food is available),
    and breeders.
    They would save all their medical services for those who truly deserve it:
    atheist pro-animal rights vegan antinatalists.
    Clearly, medical people just make up these procedures as they go along:
    clearly, they have NOT done surgeries and drawing blood and other procedures hundreds of times. Again, IF they did, then they would clearly tell the patients the cost BEFORE a procedure is done.

    But this is not surprising, since medical personnel do not have the brains or skills
    to push a button once a year for someone OTHER than the mainstream political parties (this goes for ALL nations, not just USA: I can’t stand this anti-American crap).

    This Hippocratic Oath garbage is just extreme political correctness.

    When somebody mathematically proves, from the Schrodinger wave equation modeling the atoms, all the way up, that pancreatic cancer or dementia or diseases old people get are a “negative thing”, then I will say “oops, ok.. now I have the evidence to change my mind”.

    The fact is that I have no respect for medical people.
    But, I just tell them that just so I can get treatments done for me.
    They don’t need nor deserve thanks. They already get paid enough.
    If they don’t like the job, then they’d quite and let people do their own surgery and medical care.

  10. windriven says:

    Who knew god has a sense of humor?

    So god, get with the smiting and the plagues and the raisings of the dead already. And while you’re raising I’d consider it a treat if you’d raise Christopher Hitchens.

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