Understanding anesthesia through functional imaging.
OBJECTIVE
This review will highlight the recent functional magnetic resonance imaging, positron emission tomogram scan and connectivity studies in anesthesia and analgesia.


RESULTS
In regional cerebral blood flow (rCBF) studies with isoflurane and sevoflurane, there is a consistent pattern of rise in rCBF in the anterior cingulate cortex and insula while the thalamus, lingual cortex and cerebellum show a decrease in rCBF, in a dose range of 0.2-1 minimum alveolar concentration. Even 0.25 minimum alveolar concentration causes a predominant decrease of rCBF in the cortical regions and increase of rCBF in the subcortical regions. This minimum alveolar concentration level primarily affects the association cortices. Thalamus and thalamo-cortical pathways seem to be linked to the hypnotic effects of anesthesia and deep sedation. Connectivity studies also confirm this. The electroencephalogram equivalent of this appears to be a transition from 'alpha' wave activity to 'delta' wave activity. Anterior cingulate cortex, S1 and S2 are the regions consistently activated in acute pain. Remifentanil infusion in acute pain decreases the activation in pain perception regions while activating the pain modulation regions. In chronic pain states, prefrontal cortex and insula are activated whereas there is a decrease in activity in the thalamus.


CONCLUSIONS
Slowly, a pattern of neuronal activity reflecting hypnosis, analgesia, amnesia and reflex suppression seems to be emerging giving us a better insight into the central nervous system effects of anesthesia.
Ramani
Ramachandran
R
Yale University School of Medicine, New Haven, Connecticut 06520-8051, USA. ramachandran.ramani@yale.edu
Wardhan
Richa
R
D000208:Acute Disease; D000758:Anesthesia / Q000379:methods*; D000776:Anesthesiology / Q000379:methods; D018685:Anesthetics, Inhalation / Q000494:pharmacology; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D001921:Brain / Q000000981:diagnostic imaging / Q000187:drug effects / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000187:drug effects; D002908:Chronic Disease; D032882:Comprehension; D004569:Electroencephalography; D006801:Humans; D008279:Magnetic Resonance Imaging; D009682:Magnetic Resonance Spectroscopy; D010146:Pain / Q000503:physiopathology; D010147:Pain Measurement / Q000295:instrumentation; D049268:Positron-Emission Tomography; D011859:Radiography; D014474:Unconsciousness / Q000139:chemically induced / Q000175:diagnosis* / Q000503:physiopathology
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous