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Re: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

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  • Robert Karl Stonjek
    ... From: Glynn Owens To: psychiatry-research@yahoogroups.com Sent: Thursday, December 01, 2011 6:51 PM Subject: RE: [psychiatry-research] News: Banishing
    Message 1 of 13 , Dec 1, 2011
      ----- Original Message -----
      Sent: Thursday, December 01, 2011 6:51 PM
      Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

      So what, Robert, *are* we talking about?  What operational criteria (which don't boil down to the same 'awareness' notion you have) can we use to determine whether 'consciousness' is present or not?  How can we ever know that 'consciousness' is there unless we talk of being conscious *of* something (even if that something's our own existence)?  What criteria can we use to say that some animals have consciousness and others don't?  Or that humans do and machines don't?  Give us some explicit and objective criteria and we have something we can discuss.  Otherwise we're back with Mulder and blind faith that "there must be something". 

       
      RKS:
      I related the current state of consciousness studies, so convincing me of something will not change the state of the discipline.
       
      But generally, consciousness can be also considered a state whereby an individual can be conscious of something.  Between these episodes of being conscious of something the individual still has consciousness (by these kind of theories).
       
      And let's not forget that 'consciousness' is used by a number of disciplines ranging from religion to medicine to philosophy, psychology and cognitive science.  Each area of interest considers the particular part of consciousness which is most suitable to them eg medicine wants to establish that consciousness functions within the normal range or within the normal range for a particular patient and so selects a few measurable parameters with which this can be determined (is the patient awake, can they speak, can they respond to questions etc etc).
       
      The idea of qualia requires that a person be more than just aware of an object.  A person in a persistent vegetative state may appear to have consciousness but be simply acting entirely reflexively and having no awareness, introspection or thought of any kind.
       
      Robert
    • Glynn Owens
      Hmmm, the fact that several different disciplines fall back on the same explanatory fictions is hardly good evidence for their veracity. Invoking qualia
      Message 2 of 13 , Dec 1, 2011

        Hmmm, the fact that several different disciplines fall back on the same explanatory fictions is hardly good evidence for their veracity.  Invoking 'qualia' doesn't help, since these are equally elusive, being bits of the thing we're trying to establish in the first place.  Nothing that's been said answers my questions as to what our criteria are for distinguishing the presence or absence of 'consciousness'.  Is what we're saying that if a person in PVS who responds to a particular stimulus is not 'conscious' , then 'consciousness' is predicated on *self*-observation?  If so, how is self-observation (as a process) distinguishably different from observation of anything else?  Of course I don't expect to persuade you, or anyone else who's committed heaps of time to trying to explain these things to accept that the work has all been pursuit of a will o' the wisp, any more than I expect to persuade a member of the clergy of the silliness of religion (and remember, many different religions and philosophies rest on the same explanatory concept of a god, but it doesn't mean there is such a thing).  But I'd dearly love to have a few operational criteria that everyone would agree on.

         

        cheers,

         

        Glynn  


        From: psychiatry-research@yahoogroups.com [psychiatry-research@yahoogroups.com] on behalf of Robert Karl Stonjek [stonjek@...]
        Sent: Thursday, 1 December 2011 9:03 p.m.
        To: Psychiatry Research
        Subject: Re: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

         

        ----- Original Message -----
        Sent: Thursday, December 01, 2011 6:51 PM
        Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

        So what, Robert, *are* we talking about?  What operational criteria (which don't boil down to the same 'awareness' notion you have) can we use to determine whether 'consciousness' is present or not?  How can we ever know that 'consciousness' is there unless we talk of being conscious *of* something (even if that something's our own existence)?  What criteria can we use to say that some animals have consciousness and others don't?  Or that humans do and machines don't?  Give us some explicit and objective criteria and we have something we can discuss.  Otherwise we're back with Mulder and blind faith that "there must be something". 

         
        RKS:
        I related the current state of consciousness studies, so convincing me of something will not change the state of the discipline.
         
        But generally, consciousness can be also considered a state whereby an individual can be conscious of something.  Between these episodes of being conscious of something the individual still has consciousness (by these kind of theories).
         
        And let's not forget that 'consciousness' is used by a number of disciplines ranging from religion to medicine to philosophy, psychology and cognitive science.  Each area of interest considers the particular part of consciousness which is most suitable to them eg medicine wants to establish that consciousness functions within the normal range or within the normal range for a particular patient and so selects a few measurable parameters with which this can be determined (is the patient awake, can they speak, can they respond to questions etc etc).
         
        The idea of qualia requires that a person be more than just aware of an object.  A person in a persistent vegetative state may appear to have consciousness but be simply acting entirely reflexively and having no awareness, introspection or thought of any kind.
         
        Robert

      • Robert Karl Stonjek
        ... From: Glynn Owens To: psychiatry-research@yahoogroups.com Sent: Thursday, December 01, 2011 7:26 PM Subject: RE: [psychiatry-research] News: Banishing
        Message 3 of 13 , Dec 1, 2011
          ----- Original Message -----
          Sent: Thursday, December 01, 2011 7:26 PM
          Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

          Hmmm, the fact that several different disciplines fall back on the same explanatory fictions is hardly good evidence for their veracity.  Invoking 'qualia' doesn't help, since these are equally elusive, being bits of the thing we're trying to establish in the first place.  Nothing that's been said answers my questions as to what our criteria are for distinguishing the presence or absence of 'consciousness'.  Is what we're saying that if a person in PVS who responds to a particular stimulus is not 'conscious' , then 'consciousness' is predicated on *self*-observation?  If so, how is self-observation (as a process) distinguishably different from observation of anything else?  Of course I don't expect to persuade you, or anyone else who's committed heaps of time to trying to explain these things to accept that the work has all been pursuit of a will o' the wisp, any more than I expect to persuade a member of the clergy of the silliness of religion (and remember, many different religions and philosophies rest on the same explanatory concept of a god, but it doesn't mean there is such a thing).  But I'd dearly love to have a few operational criteria that everyone would agree on.

           

          cheers,

           

          Glynn 

           

          RKS:
          In the case of PVS it is clear that 'consciousness' generally refers to the entire facilitation that is normally conscious rather than just a part of it.  One can lose bits of consciousness, such as perceptual inputs eg vision, and motor outputs and still be considered to have consciousness.  A loss of language (usually through stroke) also does not extinguish consciousness although clearly there is a deficit.  On the other hand, having nothing left but a few reflexes does not normally attract the label 'consciousness'.

           

          The tipping point between having and not having consciousness is very vague but we can say that there must be some point at which consciousness is clearly present and some point at which consciousness is clearly absent.

           

          Robert

        • Glynn Owens
          Like we can say there must be some point at which god exists? What you say only addresses the social rules by which people use the term consciousness , not
          Message 4 of 13 , Dec 1, 2011

            Like we can say there must be some point at which god exists?  What you say only addresses the social rules by which people use the term 'consciousness', not any objective evidence for there actually being some such thing above and beyond simple perception.  It all seems a bit vague to me, and really the notion of putting effort into explaining something which doesn't appear to have any real meaning or evidence of its existence still seems something of a pointless pastime.  I'm still waiting for the operational criteria that enable me to say some animals have consciousness and others don't, or that humans are and machines aren't..... I think I'd probably better bow out of this discussion until someone can come up with some such criteria, and leave it to the people who're happy just to make the assumption that "there is something out there".  Good luck with finding it.

             

            cheers,

             

            Glynn


            From: psychiatry-research@yahoogroups.com [psychiatry-research@yahoogroups.com] on behalf of Robert Karl Stonjek [stonjek@...]
            Sent: Thursday, 1 December 2011 10:05 p.m.
            To: Psychiatry Research
            Subject: Re: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

             

            ----- Original Message -----
            Sent: Thursday, December 01, 2011 7:26 PM
            Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

            Hmmm, the fact that several different disciplines fall back on the same explanatory fictions is hardly good evidence for their veracity.  Invoking 'qualia' doesn't help, since these are equally elusive, being bits of the thing we're trying to establish in the first place.  Nothing that's been said answers my questions as to what our criteria are for distinguishing the presence or absence of 'consciousness'.  Is what we're saying that if a person in PVS who responds to a particular stimulus is not 'conscious' , then 'consciousness' is predicated on *self*-observation?  If so, how is self-observation (as a process) distinguishably different from observation of anything else?  Of course I don't expect to persuade you, or anyone else who's committed heaps of time to trying to explain these things to accept that the work has all been pursuit of a will o' the wisp, any more than I expect to persuade a member of the clergy of the silliness of religion (and remember, many different religions and philosophies rest on the same explanatory concept of a god, but it doesn't mean there is such a thing).  But I'd dearly love to have a few operational criteria that everyone would agree on.

             

            cheers,

             

            Glynn 

             

            RKS:
            In the case of PVS it is clear that 'consciousness' generally refers to the entire facilitation that is normally conscious rather than just a part of it.  One can lose bits of consciousness, such as perceptual inputs eg vision, and motor outputs and still be considered to have consciousness.  A loss of language (usually through stroke) also does not extinguish consciousness although clearly there is a deficit.  On the other hand, having nothing left but a few reflexes does not normally attract the label 'consciousness'.

             

            The tipping point between having and not having consciousness is very vague but we can say that there must be some point at which consciousness is clearly present and some point at which consciousness is clearly absent.

             

            Robert

          • Philip Benjamin
            [Glynn Owens] It all seems a bit vague to me, and really the notion of putting effort into explaining something which doesn t appear to have any real meaning
            Message 5 of 13 , Dec 1, 2011
              [Glynn Owens] "It all seems a bit vague to me, and really the notion of putting effort into explaining something which doesn't appear to have any real meaning or evidence of its existence still seems something of a pointless pastime". 
               
              [Philip Benjamin
               
              Unfortunately for science, not very many in this field have the mental fortitude, or is it honesty, to say so. This word, "consciousness" crept into the literature with no scientific warrants. It was first introduced in the "Parliament of World's Religions" in Chicago, 1893 by Swami Vivekananda. However, its introduction via Tao Physics into the FAULTY  INTERPRETATION of quantum mechanics (QM), not QM theory itself, is what gave it the false 'scientific' status it enjoys. Many physicists includin Einstein vigorously objected, but the occultist physicists and psychologists (Carl Young included who had an apprenticeship in sorcery) persisted and prevailed.  A few folks in the medical profession, some well meaning and others with monetary motives via New Age publications, were facinated with "consciousness collapsing wave functions". Presto, when this collapse happens in some "quantum-level" tiny capillary-like structures CONSCIOUSNESS (whatever that be!) occurs. These tiny tubules are ubiquitous in the body, but they BELIEVE Life And Consciousness exist because of the polymers of the protein tubulin arranged in hexagonal lattices in the highly ordered networks of the "cytoskeleton" comprised of microtubules and other filamentous structures which organize cellular activities. [In paramecium all aspects of coordinated functions are accomplished by microtubules, including sensory input and movement, cell division ("mitosis"), cell growth, synapse formation etc. These are the cylindrical polymers of the protein tubulin arranged in hexagonal lattices comprising the cylinder wall].
               
              Surprisingly and irreconcilably, while in the Copenhagen INTERPRETATION of QM which Einstein and others vigorously objected as ludicrous consciousness is the CAUSE of the collapse of the wave functions, in this "medical interpretation" consciousness is the EFFECT of the collapse of the wavefunctions in the microtubules. That is a medico-physical circular reasoning. Nobody is questioning it as fundamentally flawed, but this fallacy has gone deep into the the psyche of the "acade-media" hybrid, causing enormous confusion, especially in the MINDS of freshman classes!! 


               Best regards 

               

              Philip Benjamin

               

               

               

               

              http://biodarkmatter.webs.com/index.htm

              Spiritual Body or Physical Spirit?

              Bioaxions & Extraordinary Materialism 

               


               

              To: psychiatry-research@yahoogroups.com
              From: g.owens@...
              Date: Thu, 1 Dec 2011 10:02:49 +0000
              Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

               

              Like we can say there must be some point at which god exists?  What you say only addresses the social rules by which people use the term 'consciousness', not any objective evidence for there actually being some such thing above and beyond simple perception.  It all seems a bit vague to me, and really the notion of putting effort into explaining something which doesn't appear to have any real meaning or evidence of its existence still seems something of a pointless pastime.  I'm still waiting for the operational criteria that enable me to say some animals have consciousness and others don't, or that humans are and machines aren't..... I think I'd probably better bow out of this discussion until someone can come up with some such criteria, and leave it to the people who're happy just to make the assumption that "there is something out there".  Good luck with finding it.
               
              cheers,
               
              Glynn


              From: psychiatry-research@yahoogroups.com [psychiatry-research@yahoogroups.com] on behalf of Robert Karl Stonjek [stonjek@...]
              Sent: Thursday, 1 December 2011 10:05 p.m.
              To: Psychiatry Research
              Subject: Re: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

               

              ----- Original Message -----
              Sent: Thursday, December 01, 2011 7:26 PM
              Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

              Hmmm, the fact that several different disciplines fall back on the same explanatory fictions is hardly good evidence for their veracity.  Invoking 'qualia' doesn't help, since these are equally elusive, being bits of the thing we're trying to establish in the first place.  Nothing that's been said answers my questions as to what our criteria are for distinguishing the presence or absence of 'consciousness'.  Is what we're saying that if a person in PVS who responds to a particular stimulus is not 'conscious' , then 'consciousness' is predicated on *self*-observation?  If so, how is self-observation (as a process) distinguishably different from observation of anything else?  Of course I don't expect to persuade you, or anyone else who's committed heaps of time to trying to explain these things to accept that the work has all been pursuit of a will o' the wisp, any more than I expect to persuade a member of the clergy of the silliness of religion (and remember, many different religions and philosophies rest on the same explanatory concept of a god, but it doesn't mean there is such a thing).  But I'd dearly love to have a few operational criteria that everyone would agree on.
               
              cheers,
               
              Glynn 
               
              RKS:
              In the case of PVS it is clear that 'consciousness' generally refers to the entire facilitation that is normally conscious rather than just a part of it.  One can lose bits of consciousness, such as perceptual inputs eg vision, and motor outputs and still be considered to have consciousness.  A loss of language (usually through stroke) also does not extinguish consciousness although clearly there is a deficit.  On the other hand, having nothing left but a few reflexes does not normally attract the label 'consciousness'.

               
              The tipping point between having and not having consciousness is very vague but we can say that there must be some point at which consciousness is clearly present and some point at which consciousness is clearly absent.
               
              Robert


            • Fred Weizmann
              You have just enunciated the first principle of phenomenonlogy--intentionality. Conscious is relational, it always intends an object . This view is embodied
              Message 6 of 13 , Dec 1, 2011
                You have just enunciated the first principle of phenomenonlogy--intentionality. Conscious is relational, it always "intends" an "object". This view is embodied in William James' essay "Does Consciousness Exist," in which James concludes that 'pure' consciousness--over and above our consciousness of some thing-- does not exist.  I wish more people would read it (I think it is in his "Essays in Radical Empiricism.").

                Fred Weizmann

                On 12/1/2011 1:51 AM, Glynn Owens wrote:  

                I once heard that Freddie Ayer had dismissed existentialism by noting that the whole philosophy rested on a misunderstanding of the verb "to be".  One can say the same thing about "consciousness" - this word, which we use without anything like an agreed definition (and are then, amazingly, surprised that we can't find an agree explanation) rests upon a misunderstanding of "to be conscious". - like "to be" in existentialism, it's taken as intransitive.  Once we recognise that it's transitive - "to be conscious of...." it becomes apparent that there's nothing to explain other than the simple process of perceiving, already well understood (a good place to start is Terrace's analysis of stimulus control). 

                 

                Of course like that other great indefinable "free will" there's a determined attempt to believe that "there must be something out there".  Reminds me of Mulder in the X-Files. :-)

                 

                cheers,

                 

                Glynn


                From: psychiatry-research@yahoogroups.com [psychiatry-research@yahoogroups.com] on behalf of Robert Karl Stonjek [stonjek@...]
                Sent: Thursday, 1 December 2011 7:40 p.m.
                To: Psychiatry Research; Mind and Brain; Evolutionary Psychology; Evol-Psych-News; Cognitive Neuroscience
                Subject: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

                 

                Banishing consciousness: the mystery of anaesthesia

                <i>(Image: George
Doyle/Stockbyte/Getty)</i> (Image: George Doyle/Stockbyte/Getty)

                I WALK into the operating theatre feeling vulnerable in a draughty gown and surgical stockings. Two anaesthetists in green scrubs tell me to stash my belongings under the trolley and lie down. "Can we get you something to drink from the bar?" they joke, as one deftly slides a needle into my left hand.

                I smile weakly and ask for a gin and tonic. None appears, of course, but I begin to feel light-headed, as if I really had just knocked back a stiff drink. I glance at the clock, which reads 10.10 am, and notice my hand is feeling cold. Then, nothing.

                I have had two operations under general anaesthetic this year. On both occasions I awoke with no memory of what had passed between the feeling of mild wooziness and waking up in a different room. Both times I was told that the anaesthetic would make me feel drowsy, I would go to sleep, and when I woke up it would all be over.

                What they didn't tell me was how the drugs would send me into the realms of oblivion. They couldn't. The truth is, no one knows.

                The development of general anaesthesia has transformed surgery from a horrific ordeal into a gentle slumber. It is one of the commonest medical procedures in the world, yet we still don't know how the drugs work. Perhaps this isn't surprising: we still don't understand consciousness, so how can we comprehend its disappearance?

                That is starting to change, however, with the development of new techniques for imaging the brain or recording its electrical activity during anaesthesia. "In the past five years there has been an explosion of studies, both in terms of consciousness, but also how anaesthetics might interrupt consciousness and what they teach us about it," says George Mashour, an anaesthetist at the University of Michigan in Ann Arbor. "We're at the dawn of a golden era."

                Consciousness has long been one of the great mysteries of life, the universe and everything. It is something experienced by every one of us, yet we cannot even agree on how to define it. How does the small sac of jelly that is our brain take raw data about the world and transform it into the wondrous sensation of being alive? Even our increasingly sophisticated technology for peering inside the brain has, disappointingly, failed to reveal a structure that could be the seat of consciousness.

                Altered consciousness doesn't only happen under a general anaesthetic of course - it occurs whenever we drop off to sleep, or if we are unlucky enough to be whacked on the head. But anaesthetics do allow neuroscientists to manipulate our consciousness safely, reversibly and with exquisite precision.

                It was a Japanese surgeon who performed the first known surgery under anaesthetic, in 1804, using a mixture of potent herbs. In the west, the first operation under general anaesthetic took place at Massachusetts General Hospital in 1846. A flask of sulphuric ether was held close to the patient's face until he fell unconscious.

                Since then a slew of chemicals have been co-opted to serve as anaesthetics, some inhaled, like ether, and some injected. The people who gained expertise in administering these agents developed into their own medical specialty. Although long overshadowed by the surgeons who patch you up, the humble "gas man" does just as important a job, holding you in the twilight between life and death.

                Consciousness may often be thought of as an all-or-nothing quality - either you're awake or you're not - but as I experienced, there are different levels of anaesthesia (see diagram). "The process of going into and out of general anaesthesia isn't like flipping a light switch," says Mashour. "It's more akin to a dimmer switch."

                A typical subject first experiences a state similar to drunkenness, which they may or may not be able to recall later, before falling unconscious, which is usually defined as failing to move in response to commands. As they progress deeper into the twilight zone, they now fail to respond to even the penetration of a scalpel - which is the point of the exercise, after all - and at the deepest levels may need artificial help with breathing.

                These days anaesthesia is usually started off with injection of a drug called propofol, which gives a rapid and smooth transition to unconsciousness, as happened with me. (This is also what Michael Jackson was allegedly using as a sleeping aid, with such unfortunate consequences.) Unless the operation is only meant to take a few minutes, an inhaled anaesthetic, such as isoflurane, is then usually added to give better minute-by-minute control of the depth of anaesthesia.

                Lock and key

                So what do we know about how anaesthetics work? Since they were first discovered, one of the big mysteries has been how the members of such a diverse group of chemicals can all result in the loss of consciousness. Other drugs work by binding to receptor molecules in the body, usually proteins, in a way that relies on the drug and receptor fitting snugly together like a key in a lock. Yet the long list of anaesthetic agents ranges from large complex molecules such as barbiturates or steroids, to the inert gas xenon, which exists as mere atoms. How could they all fit the same lock?

                For a long time there was great interest in the fact that the potency of anaesthetics correlates strikingly with how well they dissolve in olive oil. The popular "lipid theory" said that instead of binding to specific protein receptors, the anaesthetic physically disrupted the fatty membranes of nerve cells, causing them to malfunction.

                In the 1980s, though, experiments in test tubes showed that anaesthetics could bind to proteins in the absence of cell membranes. Since then, protein receptors have been found for many anaesthetics. Propofol, for instance, binds to receptors on nerve cells that normally respond to a chemical messenger called GABA. Presumably the solubility of anaesthetics in oil affects how easily they reach the receptors bound in the fatty membrane.

                But that solves only a small part of the mystery. We still don't know how this binding affects nerve cells, and which neural networks they feed into. "If you look at the brain under both xenon and propofol anaesthesia, there are striking similarities," says Nick Franks of Imperial College London, who overturned the lipid theory in the 1980s. "They must be triggering some common neuronal change and that's the big mystery."

                Many anaesthetics are thought to work by making it harder for neurons to fire, but this can have different effects on brain function, depending on which neurons are being blocked. So brain-imaging techniques such as functional MRI scanning, which tracks changes in blood flow to different areas of the brain, are being used to see which regions of the brain are affected by anaesthetics. Such studies have been successful in revealing several areas that are deactivated by most anaesthetics. Unfortunately, so many regions have been implicated it is hard to know which, if any, are the root cause of loss of consciousness.

                But is it even realistic to expect to find a discrete site or sites acting as the mind's "light switch"? Not according to a leading theory of consciousness that has gained ground in the past decade, which states that consciousness is a more widely distributed phenomenon. In this "global workspace" theory, incoming sensory information is first processed locally in separate brain regions without us being aware of it. We only become conscious of the experience if these signals are broadcast to a network of neurons spread through the brain, which then start firing in synchrony.

                The idea has recently gained support from recordings of the brain's electrical activity using electroencephalograph (EEG) sensors on the scalp, as people are given anaesthesia. This has shown that as consciousness fades there is a loss of synchrony between different areas of the cortex - the outermost layer of the brain important in attention, awareness, thought and memory (Science, vol 322, p 876).

                This process has also been visualised using fMRI scans. Steven Laureys, who leads the Coma Science Group at the University of Liège in Wallonia, Belgium, looked at what happens during propofol anaesthesia when patients descend from wakefulness, through mild sedation, to the point at which they fail to respond to commands. He found that while small "islands" of the cortex lit up in response to external stimuli when people were unconscious, there was no spread of activity to other areas, as there was during wakefulness or mild sedation (Frontiersin Systems Neuroscience, vol 4, p 160).

                A team led by Andreas Engel at the University Medical Center in Hamburg, Germany, have been investigating this process in still more detail by watching the transition to unconsciousness in slow motion. Normally it takes about 10 seconds to fall asleep after a propofol injection. Engel has slowed it down to many minutes by starting with just a small dose, then increasing it in seven stages. At each stage he gives a mild electric shock to the volunteer's wrist and takes EEG readings.

                We know that upon entering the brain, sensory stimuli first activate a region called the primary sensory cortex, which runs like a headband from ear to ear. Then further networks are activated, including frontal regions involved in controlling behaviour, and temporal regions towards the base of the brain that are important for memory storage.

                Engel found that at the deepest levels of anaesthesia, the primary sensory cortex was the only region to respond to the electric shock. "Long-distance communication seems to be blocked, so the brain cannot build the global workspace," says Engel, who presented the work at last year's Society for Neuroscience meeting in San Diego. "It's like the message is reaching the mailbox, but no one is picking it up."

                What could be causing the blockage? Engel has unpublished EEG data suggesting that propofol interferes with communication between the primary sensory cortex and other brain regions by causing abnormally strong synchrony between them. "It's not just shutting things down. The communication has changed," he says. "If too many neurons fire in a strongly synchronised rhythm, there is no room for exchange of specific messages."

                The communication between the different regions of the cortex is not just one way; there is both forward and backward signalling between the different areas. EEG studies on anaesthetised animals suggest it is the backwards signal between these areas that is lost when they are knocked out.

                Last month, Mashour's group published EEG work showing this to be important in people too. Both propofol and the inhaled anaesthetic sevoflurane inhibited the transmission of feedback signals from the frontal cortex in anaesthetised surgical patients. The backwards signals recovered at the same time as consciousness returned (PLoS One, DOI:10.1371/journal.pone.0025155). "The hypothesis is whether the preferential inhibition of feedback connectivity is what initially makes us unconscious," he says.

                Similar findings are coming in from studies of people in a coma or persistent vegetative state (PVS), who may open their eyes in a sleep-wake cycle, although remain unresponsive. Laureys, for example, has seen a similar breakdown in communication between different cortical areas in people in a coma. "Anaesthesia is a pharmacologically induced coma," he says. "That same breakdown in global neuronal workspace is occurring."

                Many believe that studying anaesthesia will shed light on disorders of consciousness such as coma. "Anaesthesia studies are probably the best tools we have for understanding consciousness in health and disease," says Adrian Owen of the University of Western Ontario in London, Canada.

                Owen and others have previously shown that people in a PVS respond to speech with electrical activity in their brain. More recently he did the same experiment in people progressively anaesthetised with propofol. Even when heavily sedated, their brains responded to speech. But closer inspection revealed that those parts of the brain that decode the meaning of speech had indeed switched off, prompting a rethink of what was happening in people with PVS (Proceedings of the National Academy of Sciences, vol 104, p 16032). "For years we had been looking at vegetative and coma patients whose brains were responding to speech and getting terribly seduced by these images, thinking that they were conscious," says Owen. "This told us that they are not conscious."

                As for my own journey back from the void, the first I remember is a different clock telling me that it is 10.45 am. Thirty-five minutes have elapsed since my last memory - time that I can't remember, and probably never will.

                "Welcome back," says a nurse sitting by my bed. I drift in and out of awareness for a further undefined period, then another nurse wheels me back to the ward, and offers me a cup of tea. As the shroud of darkness begins to lift, I contemplate what has just happened. While I have been asleep, a team of people have rolled me over, cut me open, and rummaged about inside my body - and I don't remember any of it. For a brief period of time "I" had simply ceased to be.

                My experience leaves me with a renewed sense of awe for what anaesthetists do as a matter of routine. Without really understanding how, they guide hundreds of millions of people a year as close to the brink of nothingness as it is possible to go without dying. Then they bring them safely back home again.

                Linda Geddes is a reporter at New Scientist

                Source: NewScientist
                http://www.newscientist.com/article/mg21228402.300-banishing-consciousness-the-mystery-of-anaesthesia.html

                Posted by
                Robert Karl Stonjek [Thanks Pierre Tremblay]

              • Psycho Dogg
                Sculley, I agree that you are not conscious. x-dogg ________________________________ From: Glynn Owens To:
                Message 7 of 13 , Dec 13, 2011
                  Sculley, I agree that you are not conscious.

                  x-dogg


                  From: Glynn Owens <g.owens@...>
                  To: "psychiatry-research@yahoogroups.com" <psychiatry-research@yahoogroups.com>
                  Sent: Thursday, December 1, 2011 12:51 AM
                  Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

                   
                  I once heard that Freddie Ayer had dismissed existentialism by noting that the whole philosophy rested on a misunderstanding of the verb "to be".  One can say the same thing about "consciousness" - this word, which we use without anything like an agreed definition (and are then, amazingly, surprised that we can't find an agree explanation) rests upon a misunderstanding of "to be conscious". - like "to be" in existentialism, it's taken as intransitive.  Once we recognise that it's transitive - "to be conscious of...." it becomes apparent that there's nothing to explain other than the simple process of perceiving, already well understood (a good place to start is Terrace's analysis of stimulus control). 
                   
                  Of course like that other great indefinable "free will" there's a determined attempt to believe that "there must be something out there".  Reminds me of Mulder in the X-Files. :-)
                   
                  cheers,
                   
                  Glynn

                  From: psychiatry-research@yahoogroups.com [psychiatry-research@yahoogroups.com] on behalf of Robert Karl Stonjek [stonjek@...]
                  Sent: Thursday, 1 December 2011 7:40 p.m.
                  To: Psychiatry Research; Mind and Brain; Evolutionary Psychology; Evol-Psych-News; Cognitive Neuroscience
                  Subject: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

                   

                  Banishing consciousness: the mystery of anaesthesia

                  <i>(Image: George Doyle/Stockbyte/Getty)</i> (Image: George Doyle/Stockbyte/Getty)
                  I WALK into the operating theatre feeling vulnerable in a draughty gown and surgical stockings. Two anaesthetists in green scrubs tell me to stash my belongings under the trolley and lie down. "Can we get you something to drink from the bar?" they joke, as one deftly slides a needle into my left hand.
                  I smile weakly and ask for a gin and tonic. None appears, of course, but I begin to feel light-headed, as if I really had just knocked back a stiff drink. I glance at the clock, which reads 10.10 am, and notice my hand is feeling cold. Then, nothing.
                  I have had two operations under general anaesthetic this year. On both occasions I awoke with no memory of what had passed between the feeling of mild wooziness and waking up in a different room. Both times I was told that the anaesthetic would make me feel drowsy, I would go to sleep, and when I woke up it would all be over.
                  What they didn't tell me was how the drugs would send me into the realms of oblivion. They couldn't. The truth is, no one knows.
                  The development of general anaesthesia has transformed surgery from a horrific ordeal into a gentle slumber. It is one of the commonest medical procedures in the world, yet we still don't know how the drugs work. Perhaps this isn't surprising: we still don't understand consciousness, so how can we comprehend its disappearance?
                  That is starting to change, however, with the development of new techniques for imaging the brain or recording its electrical activity during anaesthesia. "In the past five years there has been an explosion of studies, both in terms of consciousness, but also how anaesthetics might interrupt consciousness and what they teach us about it," says George Mashour, an anaesthetist at the University of Michigan in Ann Arbor. "We're at the dawn of a golden era."
                  Consciousness has long been one of the great mysteries of life, the universe and everything. It is something experienced by every one of us, yet we cannot even agree on how to define it. How does the small sac of jelly that is our brain take raw data about the world and transform it into the wondrous sensation of being alive? Even our increasingly sophisticated technology for peering inside the brain has, disappointingly, failed to reveal a structure that could be the seat of consciousness.
                  Altered consciousness doesn't only happen under a general anaesthetic of course - it occurs whenever we drop off to sleep, or if we are unlucky enough to be whacked on the head. But anaesthetics do allow neuroscientists to manipulate our consciousness safely, reversibly and with exquisite precision.
                  It was a Japanese surgeon who performed the first known surgery under anaesthetic, in 1804, using a mixture of potent herbs. In the west, the first operation under general anaesthetic took place at Massachusetts General Hospital in 1846. A flask of sulphuric ether was held close to the patient's face until he fell unconscious.
                  Since then a slew of chemicals have been co-opted to serve as anaesthetics, some inhaled, like ether, and some injected. The people who gained expertise in administering these agents developed into their own medical specialty. Although long overshadowed by the surgeons who patch you up, the humble "gas man" does just as important a job, holding you in the twilight between life and death.
                  Consciousness may often be thought of as an all-or-nothing quality - either you're awake or you're not - but as I experienced, there are different levels of anaesthesia (see diagram). "The process of going into and out of general anaesthesia isn't like flipping a light switch," says Mashour. "It's more akin to a dimmer switch."
                  A typical subject first experiences a state similar to drunkenness, which they may or may not be able to recall later, before falling unconscious, which is usually defined as failing to move in response to commands. As they progress deeper into the twilight zone, they now fail to respond to even the penetration of a scalpel - which is the point of the exercise, after all - and at the deepest levels may need artificial help with breathing.
                  These days anaesthesia is usually started off with injection of a drug called propofol, which gives a rapid and smooth transition to unconsciousness, as happened with me. (This is also what Michael Jackson was allegedly using as a sleeping aid, with such unfortunate consequences.) Unless the operation is only meant to take a few minutes, an inhaled anaesthetic, such as isoflurane, is then usually added to give better minute-by-minute control of the depth of anaesthesia.

                  Lock and key

                  So what do we know about how anaesthetics work? Since they were first discovered, one of the big mysteries has been how the members of such a diverse group of chemicals can all result in the loss of consciousness. Other drugs work by binding to receptor molecules in the body, usually proteins, in a way that relies on the drug and receptor fitting snugly together like a key in a lock. Yet the long list of anaesthetic agents ranges from large complex molecules such as barbiturates or steroids, to the inert gas xenon, which exists as mere atoms. How could they all fit the same lock?
                  For a long time there was great interest in the fact that the potency of anaesthetics correlates strikingly with how well they dissolve in olive oil. The popular "lipid theory" said that instead of binding to specific protein receptors, the anaesthetic physically disrupted the fatty membranes of nerve cells, causing them to malfunction.
                  In the 1980s, though, experiments in test tubes showed that anaesthetics could bind to proteins in the absence of cell membranes. Since then, protein receptors have been found for many anaesthetics. Propofol, for instance, binds to receptors on nerve cells that normally respond to a chemical messenger called GABA. Presumably the solubility of anaesthetics in oil affects how easily they reach the receptors bound in the fatty membrane.
                  But that solves only a small part of the mystery. We still don't know how this binding affects nerve cells, and which neural networks they feed into. "If you look at the brain under both xenon and propofol anaesthesia, there are striking similarities," says Nick Franks of Imperial College London, who overturned the lipid theory in the 1980s. "They must be triggering some common neuronal change and that's the big mystery."
                  Many anaesthetics are thought to work by making it harder for neurons to fire, but this can have different effects on brain function, depending on which neurons are being blocked. So brain-imaging techniques such as functional MRI scanning, which tracks changes in blood flow to different areas of the brain, are being used to see which regions of the brain are affected by anaesthetics. Such studies have been successful in revealing several areas that are deactivated by most anaesthetics. Unfortunately, so many regions have been implicated it is hard to know which, if any, are the root cause of loss of consciousness.
                  But is it even realistic to expect to find a discrete site or sites acting as the mind's "light switch"? Not according to a leading theory of consciousness that has gained ground in the past decade, which states that consciousness is a more widely distributed phenomenon. In this "global workspace" theory, incoming sensory information is first processed locally in separate brain regions without us being aware of it. We only become conscious of the experience if these signals are broadcast to a network of neurons spread through the brain, which then start firing in synchrony.
                  The idea has recently gained support from recordings of the brain's electrical activity using electroencephalograph (EEG) sensors on the scalp, as people are given anaesthesia. This has shown that as consciousness fades there is a loss of synchrony between different areas of the cortex - the outermost layer of the brain important in attention, awareness, thought and memory (Science, vol 322, p 876).
                  This process has also been visualised using fMRI scans. Steven Laureys, who leads the Coma Science Group at the University of Liège in Wallonia, Belgium, looked at what happens during propofol anaesthesia when patients descend from wakefulness, through mild sedation, to the point at which they fail to respond to commands. He found that while small "islands" of the cortex lit up in response to external stimuli when people were unconscious, there was no spread of activity to other areas, as there was during wakefulness or mild sedation (Frontiers in Systems Neuroscience, vol 4, p 160).
                  A team led by Andreas Engel at the University Medical Center in Hamburg, Germany, have been investigating this process in still more detail by watching the transition to unconsciousness in slow motion. Normally it takes about 10 seconds to fall asleep after a propofol injection. Engel has slowed it down to many minutes by starting with just a small dose, then increasing it in seven stages. At each stage he gives a mild electric shock to the volunteer's wrist and takes EEG readings.
                  We know that upon entering the brain, sensory stimuli first activate a region called the primary sensory cortex, which runs like a headband from ear to ear. Then further networks are activated, including frontal regions involved in controlling behaviour, and temporal regions towards the base of the brain that are important for memory storage.
                  Engel found that at the deepest levels of anaesthesia, the primary sensory cortex was the only region to respond to the electric shock. "Long-distance communication seems to be blocked, so the brain cannot build the global workspace," says Engel, who presented the work at last year's Society for Neuroscience meeting in San Diego. "It's like the message is reaching the mailbox, but no one is picking it up."
                  What could be causing the blockage? Engel has unpublished EEG data suggesting that propofol interferes with communication between the primary sensory cortex and other brain regions by causing abnormally strong synchrony between them. "It's not just shutting things down. The communication has changed," he says. "If too many neurons fire in a strongly synchronised rhythm, there is no room for exchange of specific messages."
                  The communication between the different regions of the cortex is not just one way; there is both forward and backward signalling between the different areas. EEG studies on anaesthetised animals suggest it is the backwards signal between these areas that is lost when they are knocked out.
                  Last month, Mashour's group published EEG work showing this to be important in people too. Both propofol and the inhaled anaesthetic sevoflurane inhibited the transmission of feedback signals from the frontal cortex in anaesthetised surgical patients. The backwards signals recovered at the same time as consciousness returned (PLoS One, DOI:10.1371/journal.pone.0025155). "The hypothesis is whether the preferential inhibition of feedback connectivity is what initially makes us unconscious," he says.
                  Similar findings are coming in from studies of people in a coma or persistent vegetative state (PVS), who may open their eyes in a sleep-wake cycle, although remain unresponsive. Laureys, for example, has seen a similar breakdown in communication between different cortical areas in people in a coma. "Anaesthesia is a pharmacologically induced coma," he says. "That same breakdown in global neuronal workspace is occurring."
                  Many believe that studying anaesthesia will shed light on disorders of consciousness such as coma. "Anaesthesia studies are probably the best tools we have for understanding consciousness in health and disease," says Adrian Owen of the University of Western Ontario in London, Canada.
                  Owen and others have previously shown that people in a PVS respond to speech with electrical activity in their brain. More recently he did the same experiment in people progressively anaesthetised with propofol. Even when heavily sedated, their brains responded to speech. But closer inspection revealed that those parts of the brain that decode the meaning of speech had indeed switched off, prompting a rethink of what was happening in people with PVS (Proceedings of the National Academy of Sciences, vol 104, p 16032). "For years we had been looking at vegetative and coma patients whose brains were responding to speech and getting terribly seduced by these images, thinking that they were conscious," says Owen. "This told us that they are not conscious."
                  As for my own journey back from the void, the first I remember is a different clock telling me that it is 10.45 am. Thirty-five minutes have elapsed since my last memory - time that I can't remember, and probably never will.
                  "Welcome back," says a nurse sitting by my bed. I drift in and out of awareness for a further undefined period, then another nurse wheels me back to the ward, and offers me a cup of tea. As the shroud of darkness begins to lift, I contemplate what has just happened. While I have been asleep, a team of people have rolled me over, cut me open, and rummaged about inside my body - and I don't remember any of it. For a brief period of time "I" had simply ceased to be.
                  My experience leaves me with a renewed sense of awe for what anaesthetists do as a matter of routine. Without really understanding how, they guide hundreds of millions of people a year as close to the brink of nothingness as it is possible to go without dying. Then they bring them safely back home again.
                  Linda Geddes is a reporter at New Scientist
                  Posted by
                  Robert Karl Stonjek [Thanks Pierre Tremblay]


                • Philip Benjamin
                  [Glynn Owens] One can say the same thing about consciousness - this word, which we use without anything like an agreed definition (and are then, amazingly,
                  Message 8 of 13 , Dec 14, 2011
                    [Glynn Owens]
                     
                    "One can say the same thing about "consciousness" - this word, which we use without anything like an agreed definition (and are then, amazingly, surprised that we can't find an agreed explanation) rests upon a misunderstanding of "to be conscious". - like "to be" in existentialism, it's taken as intransitive.  Once we recognise that it's transitive - "to be conscious of...." it becomes apparent that there's nothing to explain other than the simple process of perceiving, already well understood (a good place to start is Terrace's analysis of stimulus control)". 
                     
                     
                    [Philip Benjamin]
                     
                    This is very well put. Common sense demands this. Unfortunately that has been missing on the university campuses, along with critical thinking and its necessary component of a questioning spirit (Atheist Bertrand Russell's philosophic spirit,  philosophical habit of mindliberal outlook, liberal mind). The so called liberals (the "acede-medians") do question. But the what are they questioning?  Commonsense? Natural Laws? 2 +2 = 4?
                     
                    The foolishness of both/and illogic (because it is invariably either both/and or nothing, with either/or logic inevitably surfacing) has griped the minds of the academics. That results from a delusional Tao interpretation of Quantum Mechanics and a false interpretaion of Relativity without the ABSOLUTE of the speed of light. That is compounded with the uncritical mode of "no question asked" dogmatic blending of the FACT of Natural Selection with the FICTION of trans-speciation.
                     
                      Conscious and Unconscious States belong to Neuroscience and that field has done and still doing an excellent work on that. But that is not "the science of consciousness" according to the aficionados of a free floating "something mystic" consciousness (some of them call it a juice, perhaps akin to the "juice" of electricity?). Most of them believe, it collapses the wave functions and simultaneously also causes "consciousness"! If that is not circular reasoning, what is it?
                     
                    Any one questioning these illogical methods of analysis is branded with every label available and expelled or demoted or humiliated or ostracized. This is not only an assault on commonsense and academic freedom, but a deliberate attempt to destroy civilizations based on commonsense and the birthright of FREEDOM.    

                     

                     Best regards

                     

                     

                    Philip Benjamin

                     

                     

                    http://biodarkmatter.webs.com/index.htm

                    Spiritual Body or Physical Spirit?

                    Bioaxions & Extraordinary Materialism 

                     


                     

                    To: psychiatry-research@yahoogroups.com
                    From: psychotic_dogg@...
                    Date: Tue, 13 Dec 2011 12:03:00 -0800
                    Subject: Re: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

                     
                    Sculley, I agree that you are not conscious.

                    x-dogg


                    From: Glynn Owens <g.owens@...>
                    To: "psychiatry-research@yahoogroups.com" <psychiatry-research@yahoogroups.com>
                    Sent: Thursday, December 1, 2011 12:51 AM
                    Subject: RE: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

                     
                    I once heard that Freddie Ayer had dismissed existentialism by noting that the whole philosophy rested on a misunderstanding of the verb "to be".  One can say the same thing about "consciousness" - this word, which we use without anything like an agreed definition (and are then, amazingly, surprised that we can't find an agree explanation) rests upon a misunderstanding of "to be conscious". - like "to be" in existentialism, it's taken as intransitive.  Once we recognise that it's transitive - "to be conscious of...." it becomes apparent that there's nothing to explain other than the simple process of perceiving, already well understood (a good place to start is Terrace's analysis of stimulus control). 
                     
                    Of course like that other great indefinable "free will" there's a determined attempt to believe that "there must be something out there".  Reminds me of Mulder in the X-Files. :-)
                     
                    cheers,
                     
                    Glynn

                    From: psychiatry-research@yahoogroups.com [psychiatry-research@yahoogroups.com] on behalf of Robert Karl Stonjek [stonjek@...]
                    Sent: Thursday, 1 December 2011 7:40 p.m.
                    To: Psychiatry Research; Mind and Brain; Evolutionary Psychology; Evol-Psych-News; Cognitive Neuroscience
                    Subject: [psychiatry-research] News: Banishing consciousness: the mystery of anaesthesia

                     

                    Banishing consciousness: the mystery of anaesthesia

                    <i>(Image: George Doyle/Stockbyte/Getty)</i> (Image: George Doyle/Stockbyte/Getty)
                    I WALK into the operating theatre feeling vulnerable in a draughty gown and surgical stockings. Two anaesthetists in green scrubs tell me to stash my belongings under the trolley and lie down. "Can we get you something to drink from the bar?" they joke, as one deftly slides a needle into my left hand.
                    I smile weakly and ask for a gin and tonic. None appears, of course, but I begin to feel light-headed, as if I really had just knocked back a stiff drink. I glance at the clock, which reads 10.10 am, and notice my hand is feeling cold. Then, nothing.
                    I have had two operations under general anaesthetic this year. On both occasions I awoke with no memory of what had passed between the feeling of mild wooziness and waking up in a different room. Both times I was told that the anaesthetic would make me feel drowsy, I would go to sleep, and when I woke up it would all be over.
                    What they didn't tell me was how the drugs would send me into the realms of oblivion. They couldn't. The truth is, no one knows.
                    The development of general anaesthesia has transformed surgery from a horrific ordeal into a gentle slumber. It is one of the commonest medical procedures in the world, yet we still don't know how the drugs work. Perhaps this isn't surprising: we still don't understand consciousness, so how can we comprehend its disappearance?
                    That is starting to change, however, with the development of new techniques for imaging the brain or recording its electrical activity during anaesthesia. "In the past five years there has been an explosion of studies, both in terms of consciousness, but also how anaesthetics might interrupt consciousness and what they teach us about it," says George Mashour, an anaesthetist at the University of Michigan in Ann Arbor. "We're at the dawn of a golden era."
                    Consciousness has long been one of the great mysteries of life, the universe and everything. It is something experienced by every one of us, yet we cannot even agree on how to define it. How does the small sac of jelly that is our brain take raw data about the world and transform it into the wondrous sensation of being alive? Even our increasingly sophisticated technology for peering inside the brain has, disappointingly, failed to reveal a structure that could be the seat of consciousness.
                    Altered consciousness doesn't only happen under a general anaesthetic of course - it occurs whenever we drop off to sleep, or if we are unlucky enough to be whacked on the head. But anaesthetics do allow neuroscientists to manipulate our consciousness safely, reversibly and with exquisite precision.
                    It was a Japanese surgeon who performed the first known surgery under anaesthetic, in 1804, using a mixture of potent herbs. In the west, the first operation under general anaesthetic took place at Massachusetts General Hospital in 1846. A flask of sulphuric ether was held close to the patient's face until he fell unconscious.
                    Since then a slew of chemicals have been co-opted to serve as anaesthetics, some inhaled, like ether, and some injected. The people who gained expertise in administering these agents developed into their own medical specialty. Although long overshadowed by the surgeons who patch you up, the humble "gas man" does just as important a job, holding you in the twilight between life and death.
                    Consciousness may often be thought of as an all-or-nothing quality - either you're awake or you're not - but as I experienced, there are different levels of anaesthesia (see diagram). "The process of going into and out of general anaesthesia isn't like flipping a light switch," says Mashour. "It's more akin to a dimmer switch."
                    A typical subject first experiences a state similar to drunkenness, which they may or may not be able to recall later, before falling unconscious, which is usually defined as failing to move in response to commands. As they progress deeper into the twilight zone, they now fail to respond to even the penetration of a scalpel - which is the point of the exercise, after all - and at the deepest levels may need artificial help with breathing.
                    These days anaesthesia is usually started off with injection of a drug called propofol, which gives a rapid and smooth transition to unconsciousness, as happened with me. (This is also what Michael Jackson was allegedly using as a sleeping aid, with such unfortunate consequences.) Unless the operation is only meant to take a few minutes, an inhaled anaesthetic, such as isoflurane, is then usually added to give better minute-by-minute control of the depth of anaesthesia.

                    Lock and key

                    So what do we know about how anaesthetics work? Since they were first discovered, one of the big mysteries has been how the members of such a diverse group of chemicals can all result in the loss of consciousness. Other drugs work by binding to receptor molecules in the body, usually proteins, in a way that relies on the drug and receptor fitting snugly together like a key in a lock. Yet the long list of anaesthetic agents ranges from large complex molecules such as barbiturates or steroids, to the inert gas xenon, which exists as mere atoms. How could they all fit the same lock?
                    For a long time there was great interest in the fact that the potency of anaesthetics correlates strikingly with how well they dissolve in olive oil. The popular "lipid theory" said that instead of binding to specific protein receptors, the anaesthetic physically disrupted the fatty membranes of nerve cells, causing them to malfunction.
                    In the 1980s, though, experiments in test tubes showed that anaesthetics could bind to proteins in the absence of cell membranes. Since then, protein receptors have been found for many anaesthetics. Propofol, for instance, binds to receptors on nerve cells that normally respond to a chemical messenger called GABA. Presumably the solubility of anaesthetics in oil affects how easily they reach the receptors bound in the fatty membrane.
                    But that solves only a small part of the mystery. We still don't know how this binding affects nerve cells, and which neural networks they feed into. "If you look at the brain under both xenon and propofol anaesthesia, there are striking similarities," says Nick Franks of Imperial College London, who overturned the lipid theory in the 1980s. "They must be triggering some common neuronal change and that's the big mystery."
                    Many anaesthetics are thought to work by making it harder for neurons to fire, but this can have different effects on brain function, depending on which neurons are being blocked. So brain-imaging techniques such as functional MRI scanning, which tracks changes in blood flow to different areas of the brain, are being used to see which regions of the brain are affected by anaesthetics. Such studies have been successful in revealing several areas that are deactivated by most anaesthetics. Unfortunately, so many regions have been implicated it is hard to know which, if any, are the root cause of loss of consciousness.
                    But is it even realistic to expect to find a discrete site or sites acting as the mind's "light switch"? Not according to a leading theory of consciousness that has gained ground in the past decade, which states that consciousness is a more widely distributed phenomenon. In this "global workspace" theory, incoming sensory information is first processed locally in separate brain regions without us being aware of it. We only become conscious of the experience if these signals are broadcast to a network of neurons spread through the brain, which then start firing in synchrony.
                    The idea has recently gained support from recordings of the brain's electrical activity using electroencephalograph (EEG) sensors on the scalp, as people are given anaesthesia. This has shown that as consciousness fades there is a loss of synchrony between different areas of the cortex - the outermost layer of the brain important in attention, awareness, thought and memory (Science, vol 322, p 876).
                    This process has also been visualised using fMRI scans. Steven Laureys, who leads the Coma Science Group at the University of Liège in Wallonia, Belgium, looked at what happens during propofol anaesthesia when patients descend from wakefulness, through mild sedation, to the point at which they fail to respond to commands. He found that while small "islands" of the cortex lit up in response to external stimuli when people were unconscious, there was no spread of activity to other areas, as there was during wakefulness or mild sedation (Frontiers in Systems Neuroscience, vol 4, p 160).
                    A team led by Andreas Engel at the University Medical Center in Hamburg, Germany, have been investigating this process in still more detail by watching the transition to unconsciousness in slow motion. Normally it takes about 10 seconds to fall asleep after a propofol injection. Engel has slowed it down to many minutes by starting with just a small dose, then increasing it in seven stages. At each stage he gives a mild electric shock to the volunteer's wrist and takes EEG readings.
                    We know that upon entering the brain, sensory stimuli first activate a region called the primary sensory cortex, which runs like a headband from ear to ear. Then further networks are activated, including frontal regions involved in controlling behaviour, and temporal regions towards the base of the brain that are important for memory storage.
                    Engel found that at the deepest levels of anaesthesia, the primary sensory cortex was the only region to respond to the electric shock. "Long-distance communication seems to be blocked, so the brain cannot build the global workspace," says Engel, who presented the work at last year's Society for Neuroscience meeting in San Diego. "It's like the message is reaching the mailbox, but no one is picking it up."
                    What could be causing the blockage? Engel has unpublished EEG data suggesting that propofol interferes with communication between the primary sensory cortex and other brain regions by causing abnormally strong synchrony between them. "It's not just shutting things down. The communication has changed," he says. "If too many neurons fire in a strongly synchronised rhythm, there is no room for exchange of specific messages."
                    The communication between the different regions of the cortex is not just one way; there is both forward and backward signalling between the different areas. EEG studies on anaesthetised animals suggest it is the backwards signal between these areas that is lost when they are knocked out.
                    Last month, Mashour's group published EEG work showing this to be important in people too. Both propofol and the inhaled anaesthetic sevoflurane inhibited the transmission of feedback signals from the frontal cortex in anaesthetised surgical patients. The backwards signals recovered at the same time as consciousness returned (PLoS One, DOI:10.1371/journal.pone.0025155). "The hypothesis is whether the preferential inhibition of feedback connectivity is what initially makes us unconscious," he says.
                    Similar findings are coming in from studies of people in a coma or persistent vegetative state (PVS), who may open their eyes in a sleep-wake cycle, although remain unresponsive. Laureys, for example, has seen a similar breakdown in communication between different cortical areas in people in a coma. "Anaesthesia is a pharmacologically induced coma," he says. "That same breakdown in global neuronal workspace is occurring."
                    Many believe that studying anaesthesia will shed light on disorders of consciousness such as coma. "Anaesthesia studies are probably the best tools we have for understanding consciousness in health and disease," says Adrian Owen of the University of Western Ontario in London, Canada.
                    Owen and others have previously shown that people in a PVS respond to speech with electrical activity in their brain. More recently he did the same experiment in people progressively anaesthetised with propofol. Even when heavily sedated, their brains responded to speech. But closer inspection revealed that those parts of the brain that decode the meaning of speech had indeed switched off, prompting a rethink of what was happening in people with PVS (Proceedings of the National Academy of Sciences, vol 104, p 16032). "For years we had been looking at vegetative and coma patients whose brains were responding to speech and getting terribly seduced by these images, thinking that they were conscious," says Owen. "This told us that they are not conscious."
                    As for my own journey back from the void, the first I remember is a different clock telling me that it is 10.45 am. Thirty-five minutes have elapsed since my last memory - time that I can't remember, and probably never will.
                    "Welcome back," says a nurse sitting by my bed. I drift in and out of awareness for a further undefined period, then another nurse wheels me back to the ward, and offers me a cup of tea. As the shroud of darkness begins to lift, I contemplate what has just happened. While I have been asleep, a team of people have rolled me over, cut me open, and rummaged about inside my body - and I don't remember any of it. For a brief period of time "I" had simply ceased to be.
                    My experience leaves me with a renewed sense of awe for what anaesthetists do as a matter of routine. Without really understanding how, they guide hundreds of millions of people a year as close to the brink of nothingness as it is possible to go without dying. Then they bring them safely back home again.
                    Linda Geddes is a reporter at New Scientist
                    Posted by
                    Robert Karl Stonjek [Thanks Pierre Tremblay]



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