fMRI and Anesthesia.

BOLD activation studies discussed vary in the anesthetic agent studied (propofol, sevoflurane, and isoflurane), the concentration of the anesthetic (mostly under 0.5MAC or equivalent doses), and the activation paradigm/functional activation. The data analysis technique also differs between the studies. Notwithstanding these variations, the results can be summarized as follows: Higher order association cortices are more sensitive to anesthesia. Higher order regions processing language and semantics (regions in the frontal cortex) are affected at a lower concentration of anesthetic as compared with regions processing auditory stimuli. Whereas primary visual activation regions in the visual cortex and the thalamus are less sensitive, higher order visual spatial attention regions in the parietal cortex are more sensitive to anesthesia. In most studies, the loss of consciousness (no response to call) is achieved at or below 0.5MAC of anesthesia.