The Secret Life of the Brain
History of the Brain 3-D Brain Anatomy Mind Illusions Scanning the Brain The Episodes:
Episode 4: The Adult Brain - Laughter

photo of woman making different faces

photo of woman making different faces

photo of woman making different faces

photo of woman making different faces
Copyright © 1999 Massachusetts Medical Society. All rights reserved.

The case of a French woman who suffered from Parkinson's disease sheds more light on the association between laughter, crying and emotions. Trying to ease the symptoms of her disease, the doctors implanted electrodes in the woman's brain. This type of Apparatus sends electric pulses to the brain region that is in charge of motor activity, causing, in most patients, a significant improvement in the motor condition. However, this time something very odd happened. Immediately after the first pulse, the patient started crying. The alarmed doctors thought they might have hurt her. But upon inquiring, the woman responded with a different explanation. "I no longer wish to live, to see anything, hear anything, feel anything. I'm fed up with life", she wept, "I'm hopeless". The doctors stopped the current right away. Then, suddenly, the woman became happy, even manic. Laughing and joking, she playfully pulled the tie of one of the doctors. A few minutes later, her normal mood was restored, as if nothing had happened. When the doctors resumed the electric current a few days later, the same scenario repeated itself.

The region that was stimulated in the woman's brain was far away from the region that caused mechanical laughter in PLC cases. This time the crying and laughing were associated with emotions; the patient believed she was laughing or crying in response to something funny or sad.

These two cases suggest that there are certain parts of the brain that associate laughter with emotions, while others just operate the physical mechanism of laughter.

Pathological cases have shown associations between laughter and crying, and have implied a connection between laughter and motor activity. However, we can learn a lot about laughter not just from pathological cases, but also from its normal manifestations.

Tickling causes laughter. Perhaps laughter is merely a reflexive reaction to some types of physical irritation? Apparently, this is not the case. A person can stick his finger into his own throat and operate the gag reflex. But no matter how hard one tries, self-tickling will not cause laughter.

Laughter is unique to human beings. Like language, we don't share it even with our closest cousins, the apes. Produced only by the most evolutionarily mature and complicated brain, many theorists hypothesize that laughter and language must be associated. The relationship between the two does not end with their coordinated appearance on the stage of evolution. Laughter can be evoked by language, causing many neuroscientists to search for a functional connection between the two.

It seems that laughter is connected to a myriad of physiological and behavioral functions, but only recently have scientists begun to bring all the parts of this jigsaw puzzle together. It will be a long time before we fully understand why C.B. laughs without being happy, why an electrical stimulation to a motor control center causes the French woman to ride an emotional roller coaster, and why certain stories or situations cause ridiculous, uncontrollable convulsions.

1.Pathological laughter and crying, Parvizi et al. (2001), Brain, Vol. 124: 1708-1719.

2.Transient Acute Depression Induced by High-Frequency Deep-Brain Stimulation, Bejjani et al. (1999), NEJM Vol. 340:1476-1480.

Written by Yanay Ofran.

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