Do you know where to tickle my brain? Anatomy of laughter

There have been several ways to figure out which areas in the brain are responsible for certain tasks. Actually, we now know that one brain region just does not come along and get activated to make us do something, there is a circuit of structures working in a network of a given task.

Laughter is not an exception. When you read the stories of scientists discovering the “funny parts” of the brain, you realize how science/research can be an interesting journey.

A group of doctors from University of California were trying to explore a 16-year old girl’s brain who has severe epilepsy by using electric currents. They touched somewhere in the brain, and the girl started laughing. There were a bunch of guys in white coats surrounding her, and there was nothing funny around, even when looking at a picture of a horse made her laughing. The doctors, not the plan for that day, buzzed somewhere close to the speech centre (in the left frontal lobe), and did not need to make jokes to make their patient laugh. They concluded that speech and laughter centres are actually close, and that point they buzzed was a place in the network of laughter in the brain. More on that story, on circuit of laughter and an interesting story from early 1930s, about a guy who could not help laughing for a long period of time after showing up at the grave of his mother is here.

Actually lesions that exist in the brain give us ideas about the functions of the brain. In epilepsy seizures might rise from lesions. In the case where the patient has hypothalamic hamartomas that cause seizures, we observe the ictal laughter, where the patient is laughing during his seizure.

Epilepsy is an umbrella term for a long list of conditions with seizures. Gelastic seizures are a very rare form of epilepsy and the patients with gelastic seizures show this “ictal laughter” symptoms; recurrent bursts of laughter voices without mirth.

A case study (free on-line) on ictal laughter

Laughing consists of an affective and a motor component. It has been suggested that the affective component may result from an involvement of temporobasal structures, whereas the motor part is related to an involvement of the mesial frontal cortex. (The medial frontal lobe; also see “psychopathology of frontal lobe syndromes “;an informative page).

A 49-year-old woman with epilepsy had this laughter symptom originated from orbitofrontal cortex which is considered as a rare site of “ictal laughter”.

A 35-year-old woman with a lesion in the right supplementary sensorimotor area (SSMA) with epilepsy was investigated by stimulating the areas in her brain, and the researchers concluded that he anterior portion of the SSMA/lateral premotor cortex is involved in generating the motor pattern of laughter.

Pathological laughter is not seen only in epileptic patients but in other neurological disorders. It is also seen in patients with Alzheimer disease, and in patients with multiple sclerosis.

Here is a nice paper (free on-line) talking about the anatomy of humour:

Functional Anatomy of Humor: Positive Affect and Chronic Mental Illness

Katherine H. Taber, Ph.D., Maurice Redden, M.D., Robin A. Hurley, M.D.

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