It has never been clear exactly how general anesthetics work. General anesthetics induce a coma-like state within seconds so that the patient feels no pain or discomfort during surgery. Yet scientists have known little about the mechanism of action of these drugs. Now, a study published in the Nov. 5 issue of the Proceedings of the National Academy of Sciences of the United States of America suggests that general anesthetics alter the activity of specific areas of the brain so that they are unable to communicate with other areas. Laura Lewis, a neuroscientist at the Massachusetts Institute of Technology (MIT) in Cambridge, USA, and her colleagues used microelectrodes to measure the activity of single cells and neural networks in the brains of three patients about to undergo neurosurgery for epilepsy. Each patient was administered a single dose of the general anesthetic isoproterenol, and their response to auditory stimuli was used to determine when they entered a comatose state. The researchers found that the loss of consciousness coincided with a rapid onset of brain waves known as slow oscillations. “We were surprised to find that the slow oscillations started so unexpectedly.” Lewis said, “They came on suddenly and coincided with the patient’s loss of consciousness.” The oscillations began at different times in different areas of the cerebral cortex, and individual nerve cells all apparently became inactive at the same time that they became inactive, accompanied by slow oscillations in that area. The researchers noted that the slow oscillations make the areas of the brain that specialize in processing information inefficient and prevent different areas of the brain from exchanging information with each other. Lewis said, “The finding that this oscillation is asynchronous across regions of the brain provides a new explanation for how slow oscillations affect communication between different brain regions.” However biophysicists at Imperial College London, UK, who study the mechanism of action of anesthesiology, argue that it remains unclear whether slow oscillations actually lead to a loss of consciousness, or are simply a consequence of the latter. Further research is therefore needed to determine whether the onset of slow oscillations is sufficient to induce unconsciousness. Lewis and her colleagues suggest that perhaps their subjects had different brain activity compared to normal people, due to the patients’ seizures and the medications associated with them. But the researchers think that’s highly unlikely because the electrodes they were implanted with were at least 2 centimeters away from the abnormal tissue that causes epilepsy, and also because their behavior was no different from that seen in normal people. The researchers say their findings will help improve the way anesthesia effects are monitored, as well as develop better anesthesia drugs. The researchers now intend to further investigate whether other general anesthetics work in the same way. lewis said, “It is very possible that this finding will apply to other anesthetic drugs.” General anesthetics are a class of anesthetics that act on the central nervous system, depressing it reversibly so that the user’s consciousness, sensations, and especially pain, are lost, facilitating surgical procedures.