Date Published: April 1, 2014
Publisher: Public Library of Science
Author(s): Masahiro Matsunaga, Tokiko Isowa, Kaori Yamakawa, Seisuke Fukuyama, Jun Shinoda, Jitsuhiro Yamada, Hideki Ohira, Oscar Arias-Carrion.
Happiness has been viewed as a temporary emotional state (e.g., pleasure) and a relatively stable state of being happy (subjective happiness level). As previous studies demonstrated that individuals with high subjective happiness level rated their current affective states more positively when they experience positive events, these two aspects of happiness are interrelated. According to a recent neuroimaging study, the cytosine to thymine single-nucleotide polymorphism of the human cannabinoid receptor 1 gene is associated with sensitivity to positive emotional stimuli. Thus, we hypothesized that our genetic traits, such as the human cannabinoid receptor 1 genotypes, are closely related to the two aspects of happiness. In Experiment 1, 198 healthy volunteers were used to compare the subjective happiness level between cytosine allele carriers and thymine-thymine carriers of the human cannabinoid receptor 1 gene. In Experiment 2, we used positron emission tomography with 20 healthy participants to compare the brain responses to positive emotional stimuli of cytosine allele carriers to that of thymine-thymine carriers. Compared to thymine-thymine carriers, cytosine allele carriers have a higher subjective happiness level. Regression analysis indicated that the cytosine allele is significantly associated with subjective happiness level. The positive mood after watching a positive film was significantly higher for the cytosine allele carriers compared to the thymine-thymine carriers. Positive emotion-related brain region such as the medial prefrontal cortex was significantly activated when the cytosine allele carriers watched the positive film compared to the thymine-thymine carriers. Thus, the human cannabinoid receptor 1 genotypes are closely related to two aspects of happiness. Compared to thymine-thymine carriers, the cytosine allele carriers of the human cannabinoid receptor 1 gene, who are sensitive to positive emotional stimuli, exhibited greater magnitude positive emotions when they experienced positive events and had a higher subjective happiness level.
Happiness is one of the most fundamental human goals, which has led researchers to examine the source of individual happiness. Happiness as a scientific construct has been viewed as a temporary emotional state (hedonia) and a relatively stable state of being happy (eudaimonia) –. Hedonia is usually experienced when we get the material objects and action opportunities we wish to possess or experience –. Therefore, at the least, hedonia corresponds to a psychological state of pleasure and is greatly influenced by life events or circumstances, such as health, human relationships, household income, and housing conditions –. In contrast, according to previous studies, there is a relatively stable state of being happy, which is related to the sum of one’s recent levels of affect, one’s satisfaction with life, and disposition/propensity –. Although eudaimonia may be more difficult to define scientifically, at the least, it corresponds to a subjective assessment of one’s life lived well (e.g., subjective well-being or subjective happiness level) rather than to an emotional feeling –, .
In this study, we hypothesized that the CNR1 genotypes were closely related to happiness. That is, compared to the TT carriers, the C allele carriers of the SNP of the CNR1 (rs806377), who are sensitive to positive emotional stimuli, may experience greater magnitude positive emotions when they experience positive events and may have a higher subjective happiness level.