Ketamine, an established anesthetic and increasingly popular antidepressant, dramatically reorganizes activity in the brain, as if a switch had been flipped on its active circuits, according to a new study by Penn Medicine researchers. googletag.cmd.push(function() { googletag.display('div-gpt-ad-1450190541376-1'); }); In a Nature Neuroscience paper released this month, the team described starkly changed neuronal activity patterns in the cerebral cortex of animal models after ketamine administration—observing normally active neurons that were silenced and another set that were normally quiet suddenly springing to action.