adult brain

The study of emotion was once relegated to the backwaters of neuroscience, a testament to the popular conception that what we feel exists outside our brains, acting only to intrude on normal thought. The science has changed: Emotion is now considered integral to our over-all mental health. In mapping our emotions, scientists have found that our emotional brain overlays our thinking brain: The two exist forever intertwined.

There is a critical interplay between reason and emotion. We are well aware of how brain malfunctions can cause pain, depression, and emotional paralysis. We must also understand that the brain affects positive emotional responses such as laughter, excitement, happiness, and love. Scientists have been able to pinpoint the section of the brain that causes laughter.

Some clues for the physiological basis of laughter have come from people who suffered brain injuries, strokes or neurological diseases. C.B., a landscaper in Iowa, is one of them. Three years ago, at the age of 48, C.B. suffered a stroke. Fortunately, he recovered quite well and was expected to return to his normal life. However, since the stroke, C.B. and those around him, have been perplexed by certain changes in his behavior. Though he seems healthy, and doesn't suffer any pain, occasionally, for no noticeable reason, he bursts out into uncontrollable, wild laughter. In other cases, out of the blue, he is swept into tears in a similar attack.

C.B. has joined a long list of clinical cases that are described in medical literature as pathological laughter and crying (PLC). All of these patients suffer from brain damage that has destroyed or impaired small areas in their brains. Usually, the lesions are no bigger than a few cubic millimeters. However, since the lesions do not always occur exactly in the same spot in the brain, it is hard to determine based on these cases, which brain areas are in charge of laughter. Nevertheless, PLC suggests an interesting linkage; the same tiny lesion can cause both laughter and crying. That means that the same brain regions are involved in both laughter and crying. But most surprisingly, these laughter and crying are not associated with mirth or sadness. PLC patients suffer from "mechanical laughter". The pleasant feelings, happiness, amusement or joy that usually accompanies laughter are absent. Patients like C.B. often even suffer anxiety and fear with their laughter.

The case of a French woman who suffered from Parkinson's disease sheds more light on the association between laughter, crying and emotions.