Brain imaging helps to refine our understanding of anaesthetic effect and is providing novel information that result in the formulation of hypothesis. In the studies that will be shown here as well as in many others in which various anaesthetics were used, 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, anaesthetic vapors and opiates. Although brain imaging can't give precise information on the neurophysiological mechanisms or the anatomical connectivity that underlie anaesthetic effects, it provides an anatomical target for the localization of anaesthetic sensitive neurotransmitters and a framework for the determination of the functional network affected by anaesthetic drugs.
Functional imaging of anaesthetic effects has contributed to the emergence or the reinforcement of some interesting hypothesis on mechanisms of anaesthesia. The thalamus has consistently shown marked deactivation coincident with the anaesthesia-induced loss of consciousness, appearing to be a very important target of anaesthetic effect. This is consistent with findings from other researchers interested in single cell physiology. At the cellular level, anaesthetics have been shown to cause hyper polarization and increased conductance of thalamic ventrobasal relay neurons. This would cause an inhibition of thalamic tonic firing of action potential which, considering the central role of the thalamus in the relay of afferent information and maintenance of consciousness could be well in line with the production of anesthesia.32
Study of the mechanisms of anaesthesia may also reveal the neural substrates of changes in the level of consciousness we experience daily. The use of anaesthetic drugs can be seen as a powerful tool for investigating conscious phenomena. Anaesthetics can be very precisely given to achieve precise states of altered consciousness. Once these conditions are reached, one can look at the functional neural network responsible for that state, gathering information on processes responsible for conscious behaviour.

Selected references:
Fiset P. Functional brain imaging and propofol mechanisms of action.Adv Exp Med Biol. 2003;523:115-21
Backman SB, Fiset P, Plourde G. Cholinergic mechanisms mediating anesthetic induced altered states of consciousness. Prog Brain Res. 2004;145:197-206
Fiset P, Paus T, Daloze T, Plourde G, Meuret P, Bonhomme V, Hajj-Ali N, Backman SB, Evans AC. Brain mechanisms of propofol-induced loss of consciousness in humans: a positron emission tomographic study.J Neurosci. 1999 Jul 1;19(13):5506-13