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Background: A specific personality profile, characterized by low character maturity (low scores on the self-directedness and cooperativeness character dimensions) and high scores on the novelty seeking temperament dimension of the temperament and character inventory (TCI), has been associated with aggressive antisocial behavior in male prison inmates. It has also been shown that yoga practiced in Swedish correctional facilities has positive effects on the inmates' well-being and on risk factors associated with criminal recidivism (e.g., antisocial behavior). In this study, we aimed to investigate whether the positive effect of yoga practice on inmates' behaviors could be extended to include eventual changes in their personality profile. Methods: Male prison inmates (N = 111) in Sweden participated in a randomized controlled 10-week long yoga intervention trial. Participants were randomly assigned to either a yoga group (one class a week; n = 57) or a control group (free of choice weekly physical activity; n = 54). All the inmates completed the TCI questionnaire before and after the intervention period as part of an assessment battery. Results: After the 10-week-long intervention period male inmates scored significantly lower on the novelty seeking and the harm avoidance and significantly higher on the self-directedness dimensions of the TCI. There was a significant medium strong interaction effect between time and group belonging for the self-directedness dimension of character favoring the yoga group. Conclusion: A 10-week-long yoga practice intervention among male inmates in Swedish correctional facilities increased the inmates' character maturity, improving such abilities as their capability to take responsibility, feel more purposeful, and being more self-acceptant-features that previously were found to be associated with decreased aggressive antisocial behavior. Funders: The Swedish Prison and Probation Service (2012-1551)

Additional file 1: Table S1. Correlations between the five lower order sub-scales that compose the self-directedness (SD) scale of the temperament and character inventory (N = 2714). Table S2. Correlations between the five lower order sub-scales that compose the Cooperativeness (CO) scale of the temperament and character inventory (N = 2714). Table S3. Correlations between the three lower order sub-scales that compose the self-transcendence (ST) scale of the temperament and character inventory (N = 2714).

In former days the descriptions of personality were based on typologies, reflecting the view that people do not change over time and so have a stable, life-long personality type. Later on exclusive categories were created, but during recent times the understanding of personality has changed due to more dimensional and dynamic thinking. Cloninger’s personality theory integrates concepts and research findings from neuroanatomy, neurophysiology of behavior and learning, and from developmental, social and clinical psychology. It is postulated that the behavioural systems of temperament and character are related to two major neural systems for the adaptation of experiences on various levels. The continuous interaction between temperament and character affects the personality development in both directions; temperament impacts upon character and vice versa during life. The development of the TCI was founded on the development of the biosocial theory of personality, which in turn stimulated the further development of the theory. Unfortunately this theory-based approach is not commonly used in the development of personality measurements. The development of a personality questionnaire on the basis of the theory must be viewed as a significant challenge, and this prompted my interest in dealing with and learning more about this personality assessment method. The objectives of this thesis were a critical evaluation of Cloninger’s theory; a test of its applicability in psychiatric science; and an attempt to contribute to its development. The main findings of our investigations can be described as follows: The adaptation of the Swedish version of the Temperament and Character Inventory (TCI) was successful and the seven factor structure of Cloninger’s biopsychological theory of personality theory was mainly confirmed by the Swedish normative data and by cross-cultural comparisons between data from Germany, Sweden and the U.S.A. The results concerning internal consistency and factor structure further underline that the adult version of the TCI is unsuitable for use in adolescents before age of 17 years. For the adolescents the junior TCI is recommended. Furthermore temperament dimensions seem to be more stable over time compared to the character dimensions. The gender and age differences found suggest that both have to be taken into account in research and clinical application. The results from our studies suggested that the Temperament and Character Inventory (TCI) has to be evaluated as a useful tool within the process of validation of diagnosis of a Personality Disorder (PD), especially in clinical practice where it is often difficult to recognise all a patient’s personality disturbances during a short time. Use of the TCI is likely to improve understanding, classification, and subsequently the interpretations in clinical settings.