We studied the developmental trends of temperament and character in a longitudinal population-based sample of Finnish men and women aged 20–45 years using the Temperament and Character Inventory model of personality. Personality was assessed in 1997, 2001, and 2007 (n = 2,104, 2,095, and 2,056, respectively). Mean-level changes demonstrated qualitatively distinct developmental patterns for character (self-directedness, cooperativeness, and self-transcendence) and temperament (novelty seeking, harm avoidance, reward dependence, and persistence). Character developed toward greater maturity, although self-transcendence decreased with age. However, self-transcendence was the strongest predictor of overall personality change. Cohort effects indicated lower level of self-transcendence and higher level of self-directedness and cooperativeness in younger birth cohorts. Regarding temperament, novelty seeking decreased and persistence increased slightly with age. Both high novelty seeking and high persistence predicted overall personality change. These findings suggest that temperament and character traits follow different kinds of developmental trajectories.

The ability to form and maintain attachment relations with other people is crucial for mental health and wellbeing. The origins of attachment behaviors are often assumed to be in early experiences with other people, especially with primary caregivers. Preliminary evidence suggests that serotonergic system may be involved in attachment behaviors. We examined whether the T102C variant of the serotonin receptor 2A gene moderates the effect of childhood maternal nurturance on social attachment in adulthood. The participants were 1070 women and men from the Young Finns Study with 27-year follow-up and two measurement times for the outcomes (n = 1836 person observations). Mothers reported their relationship quality with their children (participants) in childhood or adolescence. Social attachment was assessed by participant's self-reports on two measures (reward dependence scale of the Temperament and Character Inventory and the Relationship Questionnaire). High childhood maternal nurturance predicted high reward dependence and low avoidant attachment in carriers of the T/T genotype but not in the T/C or C/C genotype groups, while low maternal nurturance was associated with low reward dependence and high avoidant attachment in T/T genotype carriers but not in C allele carriers. Our result suggests that T/T genotype carriers were more influenced by their childhood nurturing environment, than their C allele carrying counterparts, thus providing evidence for differential susceptibility to childhood nurturing environment associated with the HTR2A gene.

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The relative influences of genetic and environmental factors in the development of human behavior have been a long-term topic for an intense debate. Recent behavioral genetic studies suggest focusing on the joint effect of genes and environment, and especially on the life-course developmental interplay between nature and nurture. Vulnerability to environmental adversities and sensitivity to its benefits may be conditional on genetic background, and regarding psychological outcomes, these kinds of gene · environment interactions may be of higher importance than direct gene-trait associations. In our recent series of studies, we have shown that different variants of serotonergic and dopaminergic genes may moderate the influence of environmental conditions on a range of psychological outcomes, i.e. temperament, depression, hostility, and educational attainment. These studies suggest that depending on their genotype, people may be differentially sensitive to the environmental conditions they encounter. In the light of these results it seems highly plausible that the effects of genes may become evident only when studied in the context of environmental factors.

Tuominen, L.; Salo, J.; Hirvonen, J.; Någren, K.; Laine, P.; Melartin, T.; Isometsä, E.; Viikari, J.; Cloninger, C. R.; Raitakari, O.; Hietala, J.; and Keltikangas-Järvinen, L., ,"Temperament, character and serotonin activity in the human brain: A positron emission tomography study based on a general population cohort." Psychological Medicine. 43,4. 881-894. (2012 Background. The psychobiological model of personality by Cloninger and colleagues originally hypothesized that interindividual variability in the temperament dimension ' harm avoidance ' (HA) is explained by differences in the activity of the brain serotonin system. We assessed brain serotonin transporter (5-HTT) density in vivo with positron emission tomography (PET) in healthy individuals with high or low HA scores using an ' oversampling ' study design.Method. Subjects consistently in either upper or lower quartiles for the HA trait were selected from a populationbased cohort in Finland (n=2075) with pre-existing Temperament and Character Inventory (TCI) scores. A total of 22 subjects free of psychiatric and somatic disorders were included in the matched high-and low-HA groups. The main outcome measure was regional 5-HTT binding potential (BP ND ) in high-and low-HA groups estimated with PET and [ 11 C]N,N-dimethyl-2-(2-amino-4-methylphenylthio)benzylamine ([ 11 C]MADAM). In secondary analyses, 5-HTT BP ND was correlated with other TCI dimensions.Results. 5-HTT BP ND did not differ between high-and low-HA groups in the midbrain or any other brain region. This result remained the same even after adjusting for other relevant TCI dimensions. Higher 5-HTT BP ND in the raphe nucleus predicted higher scores in ' self-directedness '.Conclusions. This study does not support an association between the temperament dimension HA and serotonin transporter density in healthy subjects. However, we found a link between high serotonin transporter density and high ' self-directedness ' (ability to adapt and control one's behaviour to fit situations in accord with chosen goals and values). We suggest that biological factors are more important in explaining variability in character than previously thought.