Anesthetic effects of propofol in the healthy human brain: functional imaging evidence

Functional imaging methods, including positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), have become important tools for studying how anesthetic drugs act in the human brain to induce the state of general anesthesia. Recent imaging studies using fMRI and PET techniques have demonstrated the regional effects of propofol on the brain. However, the pharmacological mechanism of the action of propofol in the intact human central nervous system is unclear. To explore the possible action targets of propofol in the human brain, a systematic review of the literature was performed. The literature search was performed with limiting factors of "propofol," "functional imaging," "positron emission tomography", and "functional magnetic resonance imaging" from 1966 to July 2013 (using Medline, EMBASE, CINAHL and hand searches of references). Studies meeting the inclusion criteria were reviewed and critiqued for the purpose of this literature research. Eighteen researches meeting the inclusion criteria were reviewed in terms of the appropriateness of valuation technique. In the unconscious state, propofol sharply reduces the regional glucose metabolism rate (rGMR) and regional cerebral blood flow (rCBF) in all brain regions, particularly in the thalamus. However, GMR, such as in the occipital, temporal, and frontal lobes, was obviously decreased at a sedative dosage of propofol, whereas, changes in the thalamus were not obvious. Using fMRI, several studies observed a decrease of connectivity of the thalamus versus an increase of connectivity within the pons of the brainstem during propofol-induced mild sedation. During deep sedation, propofol preserves cortical sensory reactivity, the specific thalamocortical network is moderately affected, whereas the nonspecific thalamocortical network is severely suppressed. In contrast, several recent fMRI studies are consistent on the systemic decreased effects of propofol in the frontoparietal network. Accumulating evidence suggest that propofol-induced unconsciousness is associated with a global metabolic and vascular depression in the human brain and especially with a significant reduction in the thalamocortical network and the frontoparietal network.