The effects of anesthetics on brain activity and cognitive function.

Purpose Of This Review: This review presents an overview of recent findings related to changes in brain activity with increasing anesthesia mainly obtained with brain imaging and electrophysiological techniques in humans.

Recent Findings: Recent studies have revealed that the brain as a whole is not affected to the same degree by anesthetics, but that specific brain regions (and particular cognitive processes mediated by these regions) are more sensitive to anesthesia and sedation than others. Inhibition of activity in multimodal association cortices (such as parietal and prefrontal association cortices) by sedative concentrations of anesthetics produces amnesia and attention deficits, whereas activity in unimodal cortices and in the thalamus remains largely unaffected by low doses of anesthetics. Activity in the midbrain reticular formation, thalamus, and unimodal cortices appears to be suppressed only by anesthetic concentrations causing unconsciousness. Besides those regional suppressive effects, anesthetics impair functional connections between neurons in distributed cortical and thalamocortical networks, which also contributes to the state of anesthesia.

Summary: Anesthetics produce changes in the patient's behavioral state by interacting with brain activity via at least two mechanisms: the dose-dependent global and regionally specific suppression of neuronal activity and the disruption of functional interactivity within distributed neural networks.