Spontaneous laughter as a response to stimuli that can be generically described as comical has not been widely investigated. Rather obviously, there is an inherent difficulty in examining the neuroscience of HUMOUR and comedy, and the responses to it: what is found to be funny does not easily generalize across individuals, or even within a single individual. What is comical in one context may not be in another (and indeed may be, in other contexts, irritating, offensive or embarrassing). However, laughter can be both voluntary (that is, a response to amusing stimulation) or it can be involuntary—that is to say, not under the control of an individual and apparently unrelated to any type of stimulation. The following types of studies into laughter have been conducted. (1) Certain conditions—including HAMARTOMA in the HYPOTHALAMUS and NEURINOMA in the TROCHLEAR NERVE—have been shown to produce GELASTIC SEIZURE. GELASMUS is a condition of involuntary hysterical laughter, and has nothing to do with the appreciation of humour. It is a condition often associated with a variety of other pathological signs. (2) Laughter is an emotional response (see EMOTION) and has been used as an index of emotional dysfunction (measured using questionnaires such as the EMOTIONAL LABILITY QUESTIONNAIRE). For example, following STROKE or degenerative disorders, emotions may become more labile than normal, and may appear at inappropriate times. Inappropriate emotion is a recognized feature of damage to the frontal lobes (see FRONTAL SYNDROME) but has also been found to follow damage in other, deeper, parts of the brain. For example, patients with AMYOTROPHIC LATERAL SCLEROSIS have been shown to produce both laughter and crying inappropriately (see for example, McCullagh et al., 1999). (3) The normal appreciation of humour and control of voluntary laughter has been examined using FUNCTIONAL NEUROIMAGING. Relatively little research has been done, though there is a suggestion that the frontal lobes are involved (Shammi & Stuss, 1999). Given that the appreciation of humour involves quite complex cognitive and social processes it is not surprising perhaps that frontal systems should be involved. Whether there is any possibility of characterizing any part of the brain as being uniquely involved in recognizing ‘funny’ as opposed to being involved in cognitive processes such as WORD RECOGNITION, WORKING MEMORY, OBJECT RECOGNITION, METAREPRESENTATION and so on—processes required to interpret and understand the cognitive and emotional states of ourselves and others—is very far from clear.
(4) Some speculation has occurred as to the origin of laughter and humour. Ramachandran (1998) has suggested that it might be possible to account for laughter and humour as derivatives of our past as social PRIMATES, and that they serve as signals of threat, or the removal of threat. (5) Do animals laugh? There has been speculation (in the popular press) that rats laugh. The basis of the speculation is the observation of Panksepp and his colleagues (see Knutson et al., 1998) that rats engaged in PLAY emit high frequency ultrasonic VOCALIZATIONS. Moreover, exposure to environments in which play has taken place induces more vocalization than exposure to a novel arena, and young rats appear to emit more of these vocalizations than older ones. Of course, the mental states of animals are not accessible to us (only their behaviour is) and as such one cannot know if rats are laughing in a manner that could be considered analogous to human voluntary laughter.
Knutson B., Burgdorf J. & Panksepp J. (1998) Anticipation of play elicits high-frequency ultrasonic vocalizations in young rats. Journal of Comparative Psychology 112:65–73.
McCullagh S., Moore M., Gawel M. & Feinstein A. (1999) Pathological laughing and crying in amyotrophic lateral sclerosis: an association with prefrontal cognitive dysfunction. Journal of the Neurological Sciences 169:43–48.
Ramachandran V.S. (1999) The neurology and evolution of humour, laughter, and smiling: the false alarm theory. Medical Hypotheses 51:351–354.
Shammi P. & Stuss D.T. (1999) Humor appreciation: a role of the right frontal lobe. Brain 122:657–666.
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