Wednesday, October 6, 2010

Cross-cultural personality change throughout the lifespan: a result of brain development?

It's not difficult to readily imagine the rebellious angst ridden teenager or the wise old man of very few words. McCrae, et al.’s 1999 research findings seem to have validated these prototypical depictions. They found that across various cultures (Germany, Italy, Portugal, Croatia, and South Korea) there were higher levels of neuroticism in young adults and decreases in extraversion and openness in older adults. Older adults also showed increase rates of agreeableness and conscientiousness. But why? The authors offer up some explanations such as a combination of maturational, cultural, cohort and sampling effects. They also briefly mention genetic and evolutionary influences and this is what I am particularly interested in. We know that genes are influenced by evolutionary processes and that brain development is affected by gene expression. I suggest that brain development provides the perfect explanatory mechanism for such changes in personality traits throughout the life span.

Generally, the authors found an increased level of neuroticism in the 18-21 year old range, a sensitive time wrought with angst and rebellion. This makes sense because frontal lobes, responsible for executive functioning and emotional control, are still in development (NIMH). Neurotics tend to respond poorly to environmental stress, interpret ordinary situations as threatening, and are more impulsive. These personality characteristics map well to frontal lobes that have not been fully developed.

The Big Five Personality Traits

The authors also found that adults 50+ years old evidenced lower extraversion and openness and higher agreeableness and conscientiousness. Studies have shown that extraverts demonstrate increased sensitivity to reward signals and novelty seeking, suggesting that the dopaminergic system is involved (Cohen et al., 2005; Golimbet et. al, 2007). One study found that striatal D2 receptor availability predicted socially desirable responding (Reeves et al., 2007). Additionally, age-related decline in dopamine D2 receptors is evident (Volkow et al, 1996, 2000). Taken together these studies may offer up one piece of the explanatory puzzle as to why extraversion declines in older adults.

Openness to experience has been suggested to map well with the orbitofrontal cortex, an area known for decision-making, reward processing and emotional processing (Sutin et al., 2009 ). An absence of the posterior orbital sulcus (a part of the orbitofrontal cortex) in healthy subjects has been positively associated with openness to experience (Roppongi et al., 2010). Interestingly, older adults evidence tissue loss in the orbitofrontal cortex, perhaps explaining the decrease in openness to experience found later in life (Resnick, Lamar, & Driscoll, 2007).

Orbitofrontal Cortex

In terms of agreeablness, one study found that smaller right orbitofrontal lobe volume was associated with low agreeableness while smaller left orbitofrontal volume was correlated with high agreeableness in patients with frontaltemporal dementia (Rankin et al., 2004). Perhaps in normal aging the left orbitofrontal cortex, in particular, gradually loses tissue over time.

Regarding conscientiousness, Jackson, Belota, and Head (2009) discovered that those who were rated as higher on this personality trait showed larger regional volumes in prefrontal and mediotemporal regions and less decline with advanced aging.

The influence of brain development on cross-cultural personality changes in the context of aging, particularly the orbitofrontal cortex, is well worth considering. However, one should not forget about all the other important pieces of the puzzle (i.e. maturational, cultural, cohort and sampling effects). Needless to say, further research needs to be done in order to shed light on this intriguing link between personality and the aging brain.

References:

McCrae RR, Costa PT Jr, Pedroso de Lima M, Simões A, Ostendorf F, Angleitner A, Marusić I, Bratko D, Caprara GV, Barbaranelli C, Chae JH, & Piedmont RL (1999). Age differences in personality across the adult life span: parallels in five cultures. Developmental psychology, 35 (2), 466-77 PMID: 10082017

Cohen MX, Young J, Baek JM, Kessler C, & Ranganath C (2005). Individual differences in extraversion and dopamine genetics predict neural reward responses. Brain research. Cognitive brain research, 25 (3), 851-61 PMID: 16289773

Golimbet, V., Alfimova, M., Gritsenko, I., & Ebstein, R. (2007). Relationship between dopamine system genes and extraversion and novelty seeking Neuroscience and Behavioral Physiology, 37 (6), 601-606 DOI: 10.1007/s11055-007-0058-8

Resnick SM, Lamar M, & Driscoll I (2007). Vulnerability of the orbitofrontal cortex to age-associated structural and functional brain changes. Annals of the New York Academy of Sciences, 1121, 562-75 PMID: 17846159

Reeves SJ, Mehta MA, Montgomery AJ, Amiras D, Egerton A, Howard RJ, & Grasby PM (2007). Striatal dopamine (D2) receptor availability predicts socially desirable responding. NeuroImage, 34 (4), 1782-9 PMID: 17188897

Volkow ND, Wang GJ, Fowler JS, Logan J, Gatley SJ, MacGregor RR, Schlyer DJ, Hitzemann R, & Wolf AP (1996). Measuring age-related changes in dopamine D2 receptors with 11C-raclopride and 18F-N-methylspiroperidol. Psychiatry research, 67 (1), 11-6 PMID: 8797238

Sutin AR, Beason-Held LL, Resnick SM, & Costa PT (2009). Sex differences in resting-state neural correlates of openness to experience among older adults. Cerebral cortex (New York, N.Y. : 1991), 19 (12), 2797-802 PMID: 19366871

Roppongi T, Nakamura M, Asami T, Hayano F, Otsuka T, Uehara K, Fujiwara A, Saeki T, Hayasaka S, Yoshida T, Shimizu R, Inoue T, & Hirayasu Y (2010). Posterior orbitofrontal sulcogyral pattern associated with orbitofrontal cortex volume reduction and anxiety trait in panic disorder. Psychiatry and clinical neurosciences, 64 (3), 318-26 PMID: 20602731

Rankin KP, Rosen HJ, Kramer JH, Schauer GF, Weiner MW, Schuff N, & Miller BL (2004). Right and left medial orbitofrontal volumes show an opposite relationship to agreeableness in FTD. Dementia and geriatric cognitive disorders, 17 (4), 328-32 PMID: 15178947

Jackson J, Balota DA, & Head D (2009). Exploring the relationship between personality and regional brain volume in healthy aging. Neurobiology of aging PMID: 20036035

http://www.nimh.nih.gov/health/publications/teenage-brain-a-work-in-progress-fact-sheet/index.shtml