Involuntary Laughter

Dear all, how's it going?

This week has been quite an unbearable week for me. Apparently my wisdom tooth decided to pronounce its presence. Can't laugh, talk and eat properly. Looks like there's a price to pay for wisdom huh.

Anyway, I've been reading through some of our posts again and realized that for those of us doing or who had been doing clinics at Neuro OPD, our patients more or less remain on the list for sometime. So they get passed down from student to student. Don't know if you remember your patients but can you recall any of your patients who are super giggly and high-strung on laughter?

Those patients who laugh at inappropriate times, un-funny situations or in response to pain or discomfort. Or just at anything. And when they laugh they really go into laughing fits and find it hard to suppress the laughter. Which really affects us during treatment as laughter brings up the tone, makes them lose concentration and really tires them out. Sometimes I find it difficult suppressing my own laughter cos their guffaws are really infectious(and lately because of my throbbing wisdom tooth, it makes it painful for me to laugh).

So, despite it being a really far out topic, I decided to do a little research on the cause of involuntary laughter. Just to satisfy my curiosity.




How Do We Produce Laughter: A Suggested Neuroanatomic Circuitry

First, the anterior cingulate gyrus endows experiences with emotional consciousness and is partially under frontal cortical control. The anterior cingulate is also involved in the expression of emotion, particularly emotional vocalizations such as laughter.

Second, the amygdalae in the temporal lobes feed back to the anterior cingulate for the emotional coloring of perceptions, and the temporal (parahippocampal and fusiform) cortex integrates perceptions with prior experiences.

Third, the caudal hypothalamus, the central coordination center for internal emotional changes, is an effector of laughter.

Fourth, the ventral pontomedullary center for laughter coordinates emotional vocalization, facial expression, and expirations.

Finally, bilateral corticobulbar tracts tonically suppress laughter and oppose extrapyramidal connections for emotional expression. In addition, unilateral capsular lesions may produce temporary synkinetic laughter from crossover of activated but damaged voluntary motor pathways to these extrapyramidal pathways for laughter.

Causes of Pathological Laughter (in relation to infarction and tumours)

• Pseudobulbar Palsy: Bilateral cerebrovascular disease, multiple sclerosis, head trauma, amyotrophic lateral sclerosis, progressive supranuclear palsy


• Unilateral striatocapsular region infarction


• Focal strokes and tumours affecting ventral pons and pontomesencephalic region


• Other tumour locations: tentorial edge, right prerolandic cortex


• Gelastic(Laughing) seizures(fits): hypothalamic hamartomas or mass, temporolimbic lobe, frontal(anterior cingulate) lobe

(Adapted from Mendez et al, 1999)

The pathology sounds familiar when you look at these patients case notes. Ie pontine stroke, PSR, striatocapsular infarction due to occlusion of carotid arteries. Correlates well with the clinical presentation. Really interesting. In fact, laughter is a very little researched topic and its still quite an enigma.

Hope you find this piece of information interesting too.