Research: TAKAHASHI and colleagues,

Listed in Issue 78

Abstract

TAKAHASHI and colleagues, Department of Clinical Neuroscience, Psychiatry, Osaka University Graduate School of Medicine, D3, Suita City, Osaka 565-0871, Japan, kiyotake@psy.med.osaka-u.ac.jp, investigated the effects of laughter, including the experiential aspects of laughter, on a measure of immune function, natural killer cell activity (NKCA).

Background

Positive emotions are thought to be beneficial to health and immune status. In previous studies, the effects of laughter on NKCA were examined, but results were inconclusive due to methodological limitations of the studies. The researchers therefore designed and carried out a more rigorous study to investigate the relationship between laughter and NKCA.

Methodology

In a cross-over design study, NKCA was measured in 21 healthy male subjects before and after they watched a 75-minute comedy film and a non-emotive film (control) on different days. Magnitude of laughter was measured (as an indicator of emotional expression) by electromyographic recordings (recordings of muscle electrical activity) from the left major zygomatic muscle of the face during film-watching. The subjects rated themselves on the pleasantness of the comedy film using a visual analogue scale (VAS). The researchers also rated the subjects’ mood state before and after watching the film using the Profile of Mood States (POMS) scale.

Results

Watching the comedy film resulted in significant increases in NKCA (26.5-29.4%). Watching the non-emotive film had no effect on NKCA (27.1-24.8%). Elevated NKCA was associated with lowered scores on the negative mood scales of POMS (suggesting an association with improvement of mood). No associations were found between NKCA elevation and self-rated pleasantness or magnitude of laughter. Further analysis of the subjects and data suggested that subjects with high scores of depression and anger/hostility had a suppressed NKCA response to laughter (i.e. negative mood suppressed the NKCA elevation caused by laughter). Subjects’ NKCA levels before and after watching the comic film seemed to be somewhat related to the self-rated pleasantness score they assigned the comedy film. NKCA levels per se were not correlated with magnitude of laughter measures.

Conclusion

The results indicated that elevations of NKCA and NKCA levels before and after watching a comedy film are associated with the experiential aspects of laughter rather than its expressive aspects.

References

Takahashi K et al. The elevation of natural killer cell activity induced by laughter in a crossover designed study. International Journal of Molecular Medicine 8 (6): 645-50. Dec 2001.

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