How general anesthetic works is poorly understood.
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From Nature magazine
General anesthetics induce a coma-like state within seconds, allowing patients to be operated on without feeling pain or discomfort. Yet very little is known about how these drugs work. Now research published today in the Proceedings of the National Academy of Sciences shows that they change the activity of specific regions of the brain and make it difficult for the different parts to talk to each other.
Neuroscientist Laura Lewis of the Massachusetts Institute of Technology in Cambridge and her colleagues used microelectrodes to measure the activity of single cells and networks of neurons in the brains of three people who were about to undergo neurosurgery for epilepsy. Each patient was given a single dose of the general anesthetic propofol, and their ability to respond to auditory stimuli was used to determine when they slipped into unconsciousness.
The researchers found that loss of consciousness coincided with the rapid onset of brain waves known as slow oscillations.
“We were surprised to find that slow oscillations began so abruptly,” says Lewis. “Their onset was sudden, and precisely timed to when patients lost consciousness.”
The oscillations started at different times in different regions of the cerebral cortex, and individual neurons became markedly less active overall, with their activity spiking at the same time as the slow oscillations in that region.
The researchers propose that the slow oscillations are making the processing of information within specialized brain regions less efficient, and preventing different parts of the brain from communicating with each other.
“The finding that they were asynchronous across the brain provides a new explanation for how slow oscillations could disturb communication between different brain areas,” says Lewis.
But Nick Franks, a biophysicist at Imperial College London who studies how anesthetics act, says that it is still not clear whether the slow oscillations actually cause loss of consciousness or are simply a consequence of it. Further work will be needed to determine whether the onset of slow oscillations is enough to induce unconsciousness.
Lewis and her colleagues say that it is possible that their participants may have different brain activity from healthy people because of their seizures and the medication that they had been taking for their epilepsy. But they think this is unlikely, because they placed the electrodes at least 2 centimeters away from the abnormal tissue causing the seizures, and because the behavioral effects were the same as those seen in healthy people.
The researchers say that their findings could lead to improved ways to monitor the effects of anesthesia, and to the development of better anesthetic drugs.
They now plan to investigate whether other general anesthetics act in the same way. “It's very likely that this will apply to other anesthetic drugs,” says Lewis.
This article is reproduced with permission from the magazine Nature. The article was first published on November 5, 2012.
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5 Comments
Add Comment"it is still not clear whether the slow oscillations actually cause loss of consciousness or are simply a consequence of it"
Reply | Report Abuse | Link to thisI'm not sure I understand this statement. How can an electronic reading (such as oscillations) cause a neurological state of consciousness? Wouldn't that be like saying that a map causes the roads to be built? Or telescopes create the cosmos? Even considering the brainwaves themselves seems perplexing. Brainwaves are the result of neural activity, are they not? How can a brainwave be causative?
It seems to me the loss of consciousness changes the oscillations.
"Brainwaves are the result of neural activity, are they not? How can a brainwave be causative?" I think you are taking it a little too literally. Whatever the underlying cause of the slow oscillations turns out to be, it is possibly the cause of the loss of consciousness rather than the loss of consciousness being the cause of the slow oscillations.
Reply | Report Abuse | Link to this"It seems to me the loss of consciousness changes the oscillations." what evidence do you have to support that?
An alternative possibility is that the oscillations and loss of consciousness are both caused by some separate mechanism. As always, correlation does not establish causation...
Reply | Report Abuse | Link to thisI have no evidence, but I was responding to choices that the article asked us to consider. The article put forth the causative relationship when it quotes that "slow oscillations actually cause loss of consciousness or are simply a consequence of it".
Reply | Report Abuse | Link to thisMy comment was to point out, that given the choice of the two options the article presented, I could not understand how slow oscillations could possibly cause the loss of consciousness. Therefore, the only plausible (yet unproven) option they provided was that the oscillations are a consequence of the loss of consciousness. Again, the article introduced the causative nature between oscillations and loss of consciousness, not me. My response was within the context of the article.
Jtdwyer steps out of the simple context of the article and presents the most rational association.
that is clear.
Reply | Report Abuse | Link to thisthe question is: what reaction allows such in only one part of the body?