Below the level of the cerebral cortex lies the thalamus, the brain's information relay network. Surrounding the thalamus is a group of structures, the limbic system, which is involved in survival behavior and emotions. Closely linked with the limbic system is the hypothalamus, which has overall control of the autonomic nervous system. The cingulate gyrus is involved in survival behavior. The hippocampus is involved in memory storage.
"...when you're in front of an audience and you make them laugh at a new idea, you're guiding the whole being for the moment. No one is ever more him/herself than when they really laugh. Their defenses are down. It's very Zen-like, that moment. They are completely open, completely themselves when that message hits the brain and the laugh begins. That's when new ideas can be implanted. If a new idea slips in at that moment, it has a chance to grow.” ― George Carlin, Last Words
PET scans revealed that ketamine rapidly restored bipolar depressed patients' ability to anticipate pleasurable experiences by boosting activity in the dorsal anterior cingulate cortex (yellow) and related circuitry. Picture shows PET scan data superimposed on anatomical MRI image.