The survey required the team of surgeons, led by Itzhak Fried from UCLA Medical School, to apply an electrical current to 85 specific sites on AK's brain. Suddenly, when Professor Fried stimulated one particular set of sites contained within an area the size of a postage stamp, the girl began to smile. He had inadvertently discovered a part of the brain that somehow controls smiling. It is situated in the left superior frontal gyrus, which is more or less at the top of the head. If Fried increased the current, the smile turned into a giggle, and if he increased it further, the giggle turned into raucous laughter.
Fried's discovery has significant implications for our understanding of laughter. First, smiling is only quantitatively, and not qualitatively, different from laughter. Turning the smile into a laugh did not require stimulation at a different site, it merely required more electricity. Second, if we think of the laughter mechanism as consisting of three distinct stages (seeing something funny, feeling happy, physically laughing), then this particular part of the brain supplies the second and third stages. When the brain was stimulated, the patient reported a sense of glee as well as physically laughing.
To find out about the missing first stage, Fried asked AK what was making her laugh each time he stimulated her brain. On each occasion, AK reported that whatever she happened to see was hysterically funny. In other words, the electrode caused mirth and laughter, and her brain had then associated this general sense of merriment with the object that was in her field of view. If she happened to be looking at the wall, then the wall was hilarious, and if she happened to be looking at the surgeons, then they were hilarious. She commented, "You guys are just so funny, standing around like that."
Unfortunately, it is difficult to pursue this research, because surgeons cannot meddle with a person's brain merely to explore its mirth module. One potential avenue of research, however, would be to conduct experiments using non-invasive techniques such as MRI, which is capable of creating as many as four brain images per second, enough to glimpse the brain in action. Hence, it might be possible to tell a knock-knock joke to a patient, and then watch bits of the brain come to life as the joke is digested.