Personality Traits Associated With Area and Thickness of the Brain

There are so many clues to how we behave and our personality, not only by how our brain functions, but also by its shape. Moreover, there is a risk of developing mental health disorders, according to a study conducted by an international team of researchers from the UK, Italy and the U.S. The psychologists have found that the vast variety of personality traits can be categorized into the ‘Big Five’ traits and they are:

• How moody a person is - neuroticism
• How enthusiastic a person is - extraversion
• Measure of altruism - agreeableness
• How open minded a person is - openness
• Measure of self-control - conscientiousness

This study involved the analysis of more than 500 individuals, and is available in the Human Connectome Project, funded by the National Institutes of Health. Thickness, area and amount of cortex were the three measures of the brain cortical anatomy that were analyzed by the psychologists. The brain cortex is the outer layer of the brain.

The team of researchers tried to find how these measures related to the ‘Big Five’ personality traits. Dr. Luca Passamonti from the University of Cambridge said that evolution shaped the anatomy of our brains in such a way that there was maximization of the area and folding but at the expense of reduced thickness of the cortex. The psychologist further explained that this was like stretching a rubber sheet and that the increase in surface area that was achieved was at the cost of the sheet becoming thinner. This is called the ‘cortical stretching hypothesis’.

Cortical Stretching Hypothesis

From the Department of Geriatrics at Florida State University, Dr. Antonio Terracciano, said that cortical stretching was an important evolutionary mechanism which allowed human brains to increase rapidly but which could still be contained within the skull. The skull grew at a slower rate than the brain but this process occurs during the time of development when growth occurs in the womb. However, the brain continues to grow all throughout childhood, teenage and well into adulthood. The rapid growth of the brain when compared to the slower growth of the skull is compensated by the decrease in thickness of the cortex but the area increases due to increase in folding. 

Brain Imaging Studies

The study participants as part of the Human Connectome Project were healthy volunteers who were between 22 and 36 years of age and whose brains were imaged. They had no history of any neuro-psychiatric or other illnesses.

The study found a relationship between personality traits of these individuals and differences in their brain structure, indicating that the variations may be more enhanced among individuals who were predisposed to developing neuro-psychiatric illnesses.

Big Five Personality Traits

Personality traits of each individual is different but can be broadly categorized into five major traits.

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Neuroticism

Neuroticism lowers down as we age and as we learn to handle our emotions better. High levels of neuroticism may increase the risk for people to develop neuropsychiatric disorders and was associated with an increased thickness and lowered area with reduced folding in certain regions of the cortex like the prefrontal-temporal cortices.

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Extraversion:

This indicates how outgoing a person is. The cortical thickness was more in extraversion. There was a significant negative association between extraversion and surface area and cortical volume in the superior temporal cortex and entorhinal cortex.

Conscientiousness and Agreeableness:

 The study further found that the traits of agreeableness and conscientiousness increase with age, as we progress to being more responsible and less antagonistic.

Openness:

This trait is associated with an interest for variety and novelty as well as curiosity. Physiologically, it is associated with a reduction in the thickness along with an increase in area with the presence of folding in certain prefrontal cortices.

The work supported the hypothesis that personality was associated with the maturation of the brain with the developmental process strongly influenced by the genes that are carried. The scientists state that personality may be influenced by the experience and the environment shared by the individual but there are distinct differences in the brain structure that contribute to the differences in personality as well. This suggests that there are certain influences exerted by genes which are also validated by the belief that differences in personality traits are noticed even during infancy.

Linking Brain Structure to Personality:

The association between basic personality and the structure of the brain is a vital step which will aid in

• Understanding the association between morphology of the brain and their mood, behavior and cognitive abilities.
• Understanding the relation between the function of the brain and its structure among people who seem healthy but may be prone for psychological disorders.

The current study is a continuation of their previous study where the structure of the brain of teenagers with anti-social behavior was found to be significantly different from teenagers who did not show the same behavior. 

There is an association that exists between personality variations with alteration in the neurotransmitters’ function, as well as in regional brain metabolism suggest differences in novelty seeking, reward dependence and persistence, harm avoidance which were observed in the study population.  This shows that the structural variance noticed in the normal brain regional morphology manifests behaviorally as differences in personality traits.

Reference:

1. Roberta Riccelli Nicola Toschi Salvatore Nigro Antonio Terracciano Luca Passamonti. Surface-based morphometry reveals the neuroanatomical basis of the five-factor model of personality. Social Cognitive and Affective Neuroscience. (2017) DOI: https://doi.org/10.1093/scan/nsw175

Source-Medindia