But still the chief approach of researchers was just to look for substances with chemical structures similar to proven anesthetics. One of the odder things about anesthesia is that it is nothing like sleep. During sleep, nerve cell activity actually speeds up in certain regions of the brain, producing a well-organized depression of some brain areas, specifically in motor output and sensory input regions. Under anesthesia, though, a more generalized loss of consciousness occurs that both induces amnesia and takes away any urge to flee. Studies of individual cells in the brain during anesthesia have begun to pin down at least what anesthetics do, if not how they do it.
All general anesthetics appear to shut off the brain from external stimuli.
Chemicals called neurotransmitters normally act as messengers, crossing the synapse to relay a nerve signal. Other brain chemicals, in particular one called GABA, tend to shut off the signal. But precisely how they do this remains unclear. Most of the theories fall into two main camps. In its essential form, the unitary theory suggests that anesthetics dissolve into nerve-cell membranes and produce structural change, such as membrane swelling, that results in depressed function of ion channels, receptors, and enzymes that are involved in sending nerve signals.