Laughter and the Brain Christine Kenneally There is more in common than you might guess between the following two scenarios: (a) watching Seinfeld and (b) passing low-level currents through intracranial subdural electrodes into your brain. Both have been shown to produce uproarious laughter. Proof in the first case is anecdotal; everyone knows that Seinfeld is funny. In the second case, Itzhak Fried and associates at the Medical School at the University of California, Los Angeles, discovered that a young female patient would smile when a low electrical current was applied to the supplementary motor area of her brain (i.e. part of the motor cortex), but she would burst into loud laughter when the current was turned up. The discovery, reported in Nature in 1998, occurred while the young patient was being examined for epileptic seizures; finding the relationship between neural site specific stimulation and laughing was incidental. Interestingly, the young woman attributed her laughter to people or objects that she saw and was completely unaware that the researchers were controlling her laughter. To what extent then is a sense of humor constrained or controlled by an individual’s neurological makeup and to what extent is it a social phenomenon (i.e. a learned behavior)? Because humor occupies such a special place in human relationships, many would resist the idea that laughing and making jokes could primarily be a function of preprogrammed brain circuitry. Indeed, much of the phenomenon of laughter can be explained in social terms. For instance, most people laugh more in company than when they are alone. Television laugh tracks exploit this phenomenon, enjoining viewers to laugh at otherwise unfunny sitcoms. This contagious quality of laughter can sometimes get out of control. It is not uncommon to experience an “attack of the giggles,” but there are such things as laughter epidemics. Robert Provine wrote in a 1996 issue of American Scientist of just such an outbreak in Tanganyika in 1962. What began as an isolated fit of laughter rapidly propagated from one individual to the next, eventually growing so far as to infect adjacent communities and force the closing of schools. The outbreak apparently lasted for six months. The relationship between the social function of laughter and its neurological profile is undoubtedly complex. However, as researchers discover which parts of the brain are involved when people laugh, how laughter manifests physiologically, and why a sense of humor may suffer or benefit from brain damage, a considerable amount of evidence has accrued. What is known about humor and the brain is relatively piecemeal compared to other areas of brain research; it is nevertheless intriguing, and sometimes it’s funny too. Like many medical researchers, neurologists often learn about the brain when something has gone wrong with it. A recent example was reported in the February issue of Neurology. Dr. Samuel Berkovic and his Australian research team discovered that three patients experienced mild seizures and an unexplained need to laugh as a result of small benign tumors called hypothalamic hamartomas. The hypothalamus is located deep inside the front of the brain and is implicated in emotional responses as well as regulating body temperature and appetite; larger hypothalamic hamartomas can thus result in serious behavioral problems and impaired mental abilities. But in this case, the hamartomas created an urge to laugh that, at least for one patient, occurred up to ten times a day. The mild seizures, which were precipitated by this urge, were controllable with medication, but apparently nothing repressed the patients’ desire to giggle. At least the laughter in these cases was reported to be pleasant, even though, according to Berkovic, it is a symptom that doctors should watch out for. This is because a continuing and inexplicable need to laugh could be neurological in origin not psychological, as would generally be presumed. Another symptom that doctors and patients alike should keep an eye on is laughing so much that it results in fainting. This happened to a 62-year-old man whose chuckling got so violent while he watched a television show that he fainted three times. The show? Seinfeld, naturally. In a 1997 issue of Catheterization and Cardiovascular Diagnosis, Dr. Steven Cox and colleagues from the Lahey Hitchcock Medical Center described the fainting episodes as sudden syncope (dubbed Seinfeld Syncope by the researchers) with a spontaneous recovery of consciousness. During one of these episodes (if you ever needed encouragement not to eat and watch television at the same time), the man fell face first into the evening meal only to be rescued by his wife. In addition to the rib-tickling antics of George Kostanza, the man fainted because he experienced a physiological phenomenon called the Valsalva maneuver (forced expiration against a closed airway), resulting in increased chest pressure. Because the man had artery blockages, blood flow to his brain was severely reduced when this otherwise normal phenomenon occurred. Fainting from laughter may be extreme, but most people are familiar with the sensation of weakness that can accompany a bout of hilarity, that buzzing sense of letting go that can almost disable the laugher from doing anything else at the same time. G. Lammers and colleagues at Leiden University Medical center investigated this effect and reported in a 1999 letter to Lancet that feeling faint with laughter is not simply psychological. They showed that a particular measure of motor neuron excitability called the H-reflex amplitude was markedly reduced in subjects who were shown humorous slides. They also found a similar reduction of excitation in a group of subjects who were told a series of jokes. Interestingly, it was noted also that smiling, as well as laughter, correlated with reduced H-reflex amplitude, which Lammers and colleagues concluded was, “the neurophysiological equivalent of … being ‘weak with laughter.’” While isolated cases and small samples have contributed important knowledge about humor and the brain, more has been learned from systematic studies. A number of experiments conducted over the last ten years suggest that the right side of the brain is crucial to an individual’s sense of humor. In one such experiment in 1998, Ellen Winner and her colleagues at the State University of New York investigated the ability of right hemisphere damaged individuals to comprehend joking, irony and deception. In the study reported in Brain and Language, Winner tested how well normal individuals and right hemisphere damaged individuals distinguished jokes from lies – both being speech acts that require a more than literal understanding. The individuals with right hemisphere damage were very poor at telling the difference between the two, unlike the normal group. Winner and colleagues proposed that their subjects’ difficulty was related to associated difficulties with discourse comprehension that are known to occur in individuals who have suffered damage to the right hemisphere. Winner’s suggestion is borne out by other research that has shown how important the right hemisphere is for the processing of contextual information (see Leonard and Baum, Journal of Cognitive Neuroscience, 1998). The relationship between the interpretation of humor and context and the role of the right hemisphere is confirmed in a more recent study by P. Shammi and D. T. Stuss of the University of Toronto. They measured the joke “getting” ability of individuals who had suffered trauma to the right hemisphere, specifically to the frontal lobe. A humor appreciation test may sound oxymoronic, but Shammi and Stuss’s test included gags such as the following: A teenager is being interviewed for a summer job and the boss tells him he'll get $50 a week for the first month and $75 a week after that. The possible punch lines were: (a) I'd like to take the job. When can I start? (logical but not funny); (b) That's great! I'll come back in a month (funny); (c) Hey boss, your nose is too big for your face! (slapstick). Certainly a sense of humor is an idiosyncratic trait, but on average the individuals with right frontal lobe damage did not choose the “funny” answer (b) compared to the normal individuals. Strangely, they did seem to exhibit a preference for the slapstick alternatives, suggesting that in the absence of a subtle understanding of the scenario, the funniest possibility is simple physical humor. Shammi and Stuss also tested their subjects’ ability to get visual humor like cartoons, and they found a similar pattern. They concluded that the right frontal lobe may be unique in that it integrates cognitive and emotional information –- both necessary for the seemingly instantaneous comprehension required to “get” a joke. What conclusions can the average laugher draw from this research? First, don’t watch Seinfeld and drink soup at the same time. In addition to this basic precaution, it seems that cultivating your sense of humor can be good for your brain. As well as, “exercising the chest, neck, face, abdominal muscles, diaphragm, heart and liver and emptying the lungs of stale air,” as according to Dr. William Fry, emeritus professor of Stanford Medical School, “laughter aids memory and increases alertness and concentration.” Additional interactions between the brain and the funny bone, according to Fry, include the fact that laughter floods the brain with hormones, including beta-endorphins, which are natural painkillers. So, why did the chicken cross the road? For the same reason that the priest, the rabbi, and the shaman sat in a boat, the man walked into the bar, and the woman slipped on the banana peel – to make you feel better. Sources (in the order in which they appear) Fried, I. et al. Nature; 1998; 391: 650 Provine, R. 1996 American Scientist Berkovic, S. et al. Neurology, 2000; 54:971-973 Cox, S. et al. Catheterization and Cardiovascular Diagnosis, 1997; 242 Lammers, G. et al. Lancet, 1999; 254: 838 Winner, E. et al. Brain and Language, 1998; 62 (1): 89-106 Leonard, C. & Baum, S. Journal of Cognitive NeuroScience, 1988; 499 Shammi, P. & Stuss, D.T. Brain, 1999; 122(4):657-666 Reviewed on: Apr 05, 00