Neuroscience Psychology

What causes pathological laughter?
Answered by Susan Sherwood and Discovery Fit & Health
  • Susan Sherwood

    Susan Sherwood

  • Discovery Fit & Health

    Discovery Fit & Health

  1. Imagine eating breakfast when, suddenly, you burst into uncontrollable laughter for no apparent reason. This could happen when you're driving your car, writing a report or shopping for groceries if you suffer from pathological laughter. According to the Mayo Clinic, this laughter can stem from a variety of neurological disorders and can make it extremely difficult (sometimes impossible) for individuals to control their manifestation of mirth, even if they see no humor in a situation.

    Difficulty in expression management can also present itself as pathological crying. Those who are exceptionally unlucky experience both extremes, even shifting from laughing to crying within the same situation. There may be no obvious stimulus for the hilarity or tears. In other cases the response is merely exaggerated; laughter can erupt when most people would simply smile. Sometimes the reaction contradicts the expected response to a situation, such as laughing in a serious context. Though this disorder may seem merely quirky to an outsider, handling daily life and interacting with others is stressful for those who have it.

    The medical community lacks reliable statistics for the number of people with pathological laughter and crying (PLC). It may be labeled differently, or symptoms may be confused with depression or bipolar disorder. Also, some people may not recognize PLC as a symptom and, therefore, not seek medical attention.

    PLC seems to occur most frequently among people with amyotrophic lateral sclerosis, a disease of cerebral and spinal nerve cells. Almost half of these patients have PLC symptoms. It's also relatively common (37 percent) among sufferers of cerebellar multiple system atrophy, a neurodegenerative disease. PLC is also seen, though less frequently, among victims of stroke, traumatic brain injury, multiple sclerosis, Parkinson's disease and non-cerebellar multiple system atrophy. And almost three-quarters of patients with Alzheimer's disease appear to have symptoms similar to PLC, though this may be due to an associated mood disorder.

    The specific neurological cause remains unclear, although several medications used for mood disorders have been somewhat successful in the treatment of PLC. Researchers have had positive results with certain antidepressants, such as selective serotonin reuptake inhibitors, leading some to speculate that a serotonin imbalance could be the source of the problem. Whatever the specific cause, it's no laughing matter to the PLC patients.

    Circle of friends laughing
    (Bananastock/Thinkstock)

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  2. Pathological laughter refers to an uncontrollable kind of laughter, most likely due to a medical condition. It's usually a sign of a short circuit somewhere in the nervous system. When our nervous system is functioning in a healthy way, our brain is able to send signals that control such involuntary actions as breathing and reflexes, and voluntary actions like sitting and laughing. But if there is a chemical imbalance due to a medical condition, a tumor or a birth defect, it may cause pathological laughter.

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