Patient AK was (in 1998) a 16 year old female patient who laughed when her brain was stimulated with electric current during treatment for epilepsy.

Writing in Nature, neurologist Itzhak Fried described how Electrical stimulation was applied to the cortical surface of AK's left frontal lobe while an attempt was made to locate the focus of her epileptic seizures (which were never accompanied by laughter).

Fried identified a 2 cm by 2 cm area on the left superior frontal gyrus where stimulation produced laughter consistently (over several trials). AK reported that the laughter was accompanied by a sensation of merriment or mirth. AK gave a different explanation for the laughter each time, attributing it to an (unfunny) external stimulus. Thus, laughter was attributed to the picture she was asked to name (saying "the horse is funny"), or to the sentence she was asked to read, or to persons present in the room ("you guys are just so funny... standing around").

Increasing the level of stimulation current increased the duration and intensity of laughter. For example, at low currents only a smile was present, while at higher currents a louder, contagious laughter was induced. The laughter was also accompanied by the stopping of all activities involving speech or hand movements.

Reference

Nature 391, 650 (12 February 1998);