Brain imaging in research on anesthetic mechanisms: studies with propofol.

Brain imaging helps to refine our understanding of the anesthetic effect and is providing novel information that result in the formulation of hypotheses. They have shown that anesthetics act on specific structures that have been known to be important for consciousness at large. They have also helped to show that anesthetics act on specific structures regionally, rather than being non-specific, general depressant of the central nervous system (CNS). A constant finding is that the drugs that we use seem to exert their action on specific sites within the CNS. This is true for a wide variety of drugs like midazolam, anesthetic vapors and opiates. The thalamus has consistently shown marked deactivation coincident with the anesthesia-induced loss of consciousness, appearing to be a very important target of anesthetic effect. Additionally, when vibro-tactile or pain stimulation is given, anesthetics significantly effect cortical structures even before loss of consciousness while loss of transmission at the thalamic level seems to coincide with loss of consciousness. Finally, the use of radioligands allow in vivo characterization of anesthetic effects on neurotransmitter systems.