Cortex Off, Consciousness Off
This dramatic reduction in brain activity after loss of consciousness is scarcely surprising. 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. Which region in the cortex, the thalamus or elsewhere is essential to be conscious at all? Consider the following two experiments.
Twenty-five patients with Parkinson's disease were anesthetized with propofol or sevoflurane while the electrical activity of both the cortex and thalamus was monitored by a group under François Gouin of the Timone University Hospital Center at the University of the Mediterranean in Marseille, France. Their neocortex was monitored by a conventional electroencephalographic (EEG) electrode placed on the scalp on top of the head, whereas thalamic activity was recorded by an electrode implanted deep inside the brain in the subthalamic nucleus. This electrode stimulates the brain to alleviate the shaking that is the hallmark of Parkinson's. Experimenters assessed consciousness by tapping patients on the shoulder and asking them every 20 seconds to open their eyes.
When consciousness was lost after anesthesia was initiated—that is, when the patients no longer opened their eyes following the command—the cortical EEG changed dramatically, switching from low amplitude and irregular activity into readings dominated by large and slow brain waves that occur about once every second. Such so-called delta band activity is characteristic of deep sleep. Furthermore, the complexity of the cortical EEG signal decreased significantly when patients stopped responding. None of these changes occurs in the thalamic electrode at the time that consciousness is lost.
Indeed, it is only several minutes later that the thalamic voltage signal matches that of the cortex. The data—consistent for two quite different anesthetic agents, one injected and the other one inhaled—argue that the drivers for the loss of consciousness are parts (or all) of the neocortex and that the thalamus follows.
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13 Comments
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.