Another interesting study was that by Kotyuk
Another interesting study was that by Kotyuk et al. (2015), who investigated the association between COMT rs4680 and personality in elderly people. The authors analysed the association between COMT rs4680 and NEO-FFI. The GG dopamine hydrochloride correlated with lower mean Neuroticism score and higher Agreeableness and Conscientiousness scores compared to subjects with the AA or AG genotypes. In our study, athletes with GG vs AA and GG vs AG+AA were characterized by lower sensitivity, which confirms higher resilience of the nervous system to sensory stimuli. In the control group, subjects with GG vs AG+AA genotype scored significantly lower on the perseveration scale. This trait is related to greater flexibility of behaviours and easiness in shifting attention to various sources of stimulation. Additionally, in the control group we have noted significantly higher scores in emotional reactivity in subjects with the GG genotype than in subjects with AG or AA genotypes (in athletes only for the GG vs AG genotype). We characterize them as highly reactive and less resilient individuals, who will avoid activities involving much stress and will respond with stress to intense stimulation. However, in individuals with low nervous system arousal, high reactivity is related to higher performance in sport. Subjects with the GG (Val/Val) genotype have higher COMT enzyme activity, which results in lower dopamine level. This association has been confirmed by Kucharska-Mazur et al. (2004), who noted significantly lower impulsivity in individuals with the lowest COMT activity (homozygotes Met/Met). In the study by Kotyuk et al. (2015), individuals with higher COMT activity (GG) and the resulting lower dopamine levels scored lower on Neuroticism and higher on Agreeableness and Conscientiousness. This is consistent with a recent model of phasic and tonic dopamine release suggesting that even though the GG genotype is associated with lower tonic dopamine release, the phasic release of dopamine might be optimal for a more adaptive personality profile, related to temperamental traits such as briskness, perseveration and endurance. According to Bilder, Volavka, Lachman, and Grace (2004), the Met (A) allele associated with low COMT activity increases tonic dopamine release, which inhibits phasic dopamine release. This may result in decreased sensitivity to new stimuli. The authors proposed that an analogous mechanism may be a basis for behaviour requiring reinforcement. In such a case, carriers of the Met allele, associated with a decreased level of phasic dopamine, will tend to manifest behaviours that aim at seeking high levels of additional stimulation (such as drug abuse and combat sports). It is a molecular mechanism attempting to increase dopamine to an optimum level. This model suggests that although the GG genotype is associated with lower tonic dopamine release, phasic dopamine release may be optimum for limiting reward-seeking behaviour and personality traits such as lower Neuroticism, higher Agreeableness and Conscientiousness (Bilder et al., 2004, Kotyuk et al., 2015). Research provides ample evidence for an association between changes in opioid signalling and changes in social behaviours in animals. Only a small number of studies attempted to determine whether such associations occur in people as well. Troisi et al. (2011) investigated whether a common polymorphism (A118G) in the μ-opioid receptor gene (OPRM1) is associated with alterations in personality traits linked to affiliative behaviour and attachment. In a mixed sample (N=214) of adult healthy volunteers and psychiatric patients, they analysed the association between the A118G polymorphism of OPRM1 and two different psychological constructs reflecting individual differences in the capacity to experience social reward. Carriers of the G allele had an increased tendency to become engaged in affectionate relationships, as indicated by lower avoidant attachment scores. Moreover, these individuals experienced more pleasure in social situations, as indicated by lower scores on a self-report measure of social anhedonia. The association between the A118G polymorphism and social hedonic capacity was independent of the participants\' mental health status. The results are in agreement with the brain opioid hypothesis of social attachment and the established role of opioid transmission in mediating affiliative behaviour (Troisi et al., 2011).