We take it for granted that any kind of surgical procedure, whether extracting a wisdom tooth or replacing a heart valve, will be painless and won't leave any bad memories. Every year tens of millions of patients worldwide remember being prepared for an operation—then nothing, until they wake up in the recovery room. This is the magic of general anesthesia, which safely knocks out that most precious of life's possessions, conscious experience, then reliably restores it without any lasting consequences. Of course, it was not always thus. Until the discovery of nitrous oxide as an anesthetic in the mid-19th century, surgery was an extreme and dangerous intervention of last resort whose effects could, at best, be blunted by opium or alcohol.
Today anesthesiologists can choose from an astonishing variety of chemicals to separately and independently eliminate pain (analgesia), memory (amnesia), mobility, and responsiveness to the cutting, scraping, drilling or cauterizing of the surgical procedure, and, most important from the point of view of the patient, awareness (loss of consciousness). Two types of anesthetics exist: intravenous agents that are injected into the bloodstream for the rapid induction and maintenance of anesthesia, such as barbiturates, propofol and ketamine, and inhalation agents, such as laughing gas (nitrous oxide) or vapors of volatile liquids, including isoflurane and sevoflurane.
Much is known about the molecular action of these substances. With the singular exception of the dissociative ketamine (abused at low doses as a street drug known as vitamin K or special K and not further discussed here), anesthetics strengthen neuronal inhibition either by activating inhibitory chemical synapses, which constrain activity in the neurons they are connected to, or by binding to membrane proteins that keep the electrical activity of neurons—and therefore their ability to transmit information and command—in check. Their net effect is to reduce overall brain activity. Every functional brain-imaging study carried out to date proves this point. For anesthesiologists, the technique of choice is positron emission tomography (PET), in which a small amount of radioactive tracer is injected into the bloodstream of the subject. Brain regions that are more or less active than neighboring areas consume metabolic resources in the same ratio. This metabolic activity can be reliably measured in a PET device, albeit with a crude temporal (on the order of tens of seconds) and spatial (on the order of the size of a pea) resolution.
PET imaging demonstrates that essentially all anesthetics decrease global cerebral metabolism in a dose-dependent manner. The more of the anesthetic dispensed, the bigger the activity reduction in regions of the brain stem responsible for promoting wakefulness and in the neocortex and the closely allied thalamus underneath it. The neocortex is the most recently evolved part of the cerebral cortex, the folded layers of neurons that constitute the proverbial gray matter. It occupies most of the forebrain and is a unique hallmark of mammals. The thalamus is a quail egg–size structure in the middle of the brain that regulates all input into the neocortex and receives massive feedback from it.
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Add CommentIt's not apparent whether the mind is switched off or consciousness ceases.
Reply | Report Abuse | Link to thisIs there a mind-body riddle or a conscious-mind riddle or both?
All the research studies of neuro scientists are based upon one broad hypothesis: Mind and consciousness are the off shoots of neuronal activity in brain. Why don't they think from the reverse paradigm : Neuronal activity results from mental activity? Consciousness, mind and brain are three distinct entities but intricately linked with each other and work in tandem. A reduction in the neuronal activity in different parts of brain viz neocortex, cortex and thalmus thru anaesthesia greatly reduces the manifestation of mind and consciousness to the level of brain but this does not amounts to state that mind and consciousness are primarily produced by brain.
Reply | Report Abuse | Link to thisEven under anaesthesia, all the mental and personality traits remain intact but dormant and once anaesthesia effect is over, all the mental and personality traits revert back. This itself establishes that mind is different than brain and during anaesthesia and deep sleep, it becomes deactivated. But what about consciousness? It is neither brain nor mind. An entity distinct from mind and brain --- activates mind and brain (body) and stays as the ultimate perceiver of all whatever happens in mind and body
It would be interesting to see similar studies done with people who experience mixed states of consciousness, such as lucid dreams or sleepwalking episodes. There are some people who don't completely lose consciousness when under anesthesia. (Scary!) What happens in their brains?
Reply | Report Abuse | Link to this"The link between consciousness and this organ is tight, as expressed in the adage “No brain: never mind!” Yet neuroscientists are trying to track the footprints of consciousness to its actual lair."
Reply | Report Abuse | Link to thisIn their own way do not all creatures have lairs ?
There are some funny facts related to anesthesia: not long ago, the event a patient gaining conscience while supposedly under deep anesthesia and still subject to the surgical procedure was accounted as a % of all the anesthetic acts. One of the products anesthesiologists employed to have the patient skeletal muscles relaxed, a goal first obtained by Curare-derived products, came from a Caribbean fish, the Haiti sorcerers made a preparation from that fish that they used to keep people paralyzed but conscious, they buried them, and after some time, usually days, the sorcerer took its victim out of the grave where the bewitched was put, and used him/her as a zombie for the sorcerer benefit, supposedly committing crimes for the sorcerer. The way they keep their victims paralyzed is known, the curare-like product from the fish, the rest of the process remains a mystery, as for the elusive "Golems".
Reply | Report Abuse | Link to thisWhat I don't understand is why these anesthetic drugs don't affect the neural nets controlling basic life functions, like breathing and heart beat.
Reply | Report Abuse | Link to thisI think after a certain dosage of anaesthesia neural nets controlling life vital like breathing and heart functioning should also be collapsing. Only some specialist in anaesthesia can give final answer
Reply | Report Abuse | Link to thisI speculate that neuronal activity brings the outside world to the mental world. For sound, the links are vibrations to sound waves to ear to auditory nerve to brain and then to mind.
Reply | Report Abuse | Link to thisIf mind is independent of the brain then why is there a need for any links at all?
The process that creates the mind is unknown but the pathway is through the brain. Is the mind an intangible slate that is written on by the brain or is the mental phenomenon all there is to the mind?
The source of consciousness is unknown. Could it be the brain? It could be but I don't know how to test that hypothesis.
By "speculat[ing] that neronal activity brings the outside world to the mental world", you seem to assume that the brain and mind are separate from each other. This Cartesian view is currently in disrepute among most scientists, but perhaps not among some philosophers and religionists.
Reply | Report Abuse | Link to thisOne hint that the brain must somehow be involved in consciousness is that only certain kinds of life forms exhibit some degree of consciousness and all of them happen to have brains.
The computer and monitor are different. And the output on the monitor is different than the monitor.
Reply | Report Abuse | Link to thisQualia are not brain but they are the output of brain. To say that qualia do not exists is to limit the discussion of mind and brain to just brain.
Brain is tangible but mind is not. Mind is sound, images, feelings, thoughts, tastes and smells; all intangible phenomenon.
But thanks for answering my post. Your thinking sheds light on the scientific perspective.
Also, mind exists because of consciousness or consciousness exists because of mind. (which came first?) In evolutionary terms I say that consciousness came first because mind would never evolve without consciousness. But then what did consciousness evolve from?
Reply | Report Abuse | Link to thisI'm not clear on how you distinguish "tangible" from "intangible." In what sense is the brain tangible? I can open up a human skull and "look at" the brain. Thus, it is an image. One can smell it, touch it, and taste it too, if one is "a mind to". Thus, isn't the brain also intangible?
Reply | Report Abuse | Link to thisThere are two brains: the real material brain and the brain in a persons mind. The real material brain is tangible. The brain in a person's mind is intangible.
Reply | Report Abuse | Link to thisIf you prick your finger, there is a material needle and a material finger. But you are only aware of the mind needle and the mind finger.