Personality Neuroscience: How the Brain Relates to Personality

right side of brain From Manuel de L'Anatomiste  Morel and Duval  1883On February 17, 2013, a New York Times article was the first to announce the Obama administration’s plans to unveil a long-term neuroscience project in March [1]. The multi-billion dollar, decades-long Brain Activity Map (BAM) project aims to map each of the 100 billion neurons whose activity underlies normal and diseased brain function, in an effort to better understand how we think and perceive [2]. In his State of the Union address, President Obama drew a parallel between the Human Genome Project and brain mapping, citing the financial returns brought by the former to lend credibility to the potential of the latter: “Every dollar we invested to map the human genome returned $140 to our economy—every dollar. Today our scientists are mapping the human brain to unlock the answers to Alzheimer’s…Now is not the time to gut these job-creating investments in science and innovation.” Beyond economics, however, this new undertaking emphasizes the importance of brain studies in improving our understanding of ourselves.

In superhero movies, the traits that define personality are magnified—the compassionate and brave hero fights the cackling, diabolical enemy. In our daily lives, we see more subtle shades of differences: There’s the introverted poet, the brilliant problem-solver, the sweet girl nobody can bring themselves to dislike, and the always-composed leader. Overall, there is a multitude of personalities making up the multitude of people inhabiting society, and only recently have these personality types been tied down to the biology of brain structure.

Historically, people have sought to understand personality through various means. In the Hippocratic Corpus written several thousand years ago, the theory of humorism was developed as a way to explain temperamental differences. Hippocrates attributed personality characteristics to the four bodily humors, including blood, yellow bile, black bile, and phlegm [3]. More recently in the mid-1700’s to 1800’s, phrenology arose as a scientific field of study; now debunked, it posited that skull morphology was tied to moral and intellectual development [4]. The father of phrenology, Dr. Franz Joseph Gall, listed 27 such mental faculties, including the tendency to steal and religiosity, and associated each of the 27 traits with a specific part of the skull [5].

Since then, personality has been simplified into five general domains, officially called the Big Five dimensions: extraversion, agreeableness, conscientiousness, neuroticism, and openness [6]. These five domains encompass assertiveness, insight, and irritability, among other traits, and they have been adopted by the scientific community due to their universal applicability across gender and ethnicity. The differences among these five dimensions create the differences in personality, which manifest themselves in cognition, emotion, motivation, and behavior [7]. Meanwhile, biological understanding of personality has shifted from the humors and skull structure to the brain. The brain is divided into the frontal, parietal, occipital, and temporal lobes, and these are commonly responsible for reasoning, movement, visual processing, and memory, respectively [8]. Scientists have conducted several studies to demonstrate the connection between brain structure and personality, paying particularly attention to the effect of brain malfunction on personality change.

At the Dementia Research Center in the London Institute of Neurology, scientists studied frontotemporal lobar degeneration (FTLD), a condition that is known to cause young-onset dementia due to frontal, parietal and temporal lobe atrophy [9]. FTLD also causes clear behavioral abnormalities and social dysfunction, which are strongly associated with personality change. In the study, thirty FTLD-afflicted individuals had their caregivers complete the Big Five Inventory (BFI) twice, once based on the patient’s current situation and once based on the patient’s pre-morbidity state ten years prior. The BFI, a simple 44-question test, demonstrates levels of each dimension independently of each other, and results were expressed through a numerical score in order to quantitatively measure personality change throughout the course of the disease. As a single group, patients with FTLD demonstrated significant decreases in all dimensions with the exception of neuroticism, which experienced an average increase of 0.83 on a scale of five.

With personality differences quantified, patients underwent brain MRIs and regional grey matter volumes were analyzed alongside BFI-change scores for any potential biological connection. The study showed statistically significant correlations between personality change and regional brain degeneration. The characteristically wrinkled surface of the brain is divided into the sulcus and the gyrus; the sulcus encompasses the wrinkle furrows that surround the gyrus, and the preservation of grey matter in both is associated with reduced conscientiousness and reduced agreeableness. Meanwhile, loss of grey matter in the cortex, or the largest outer portion of brain neural tissue, is significantly associated with all five trait changes. This region encompasses various lobes of the brain and, although only 2-4 mm thick, has been shown to be responsible for higher thought [10]. Subsequently, this correlation between cortex loss and deteriorating personality strongly implies the cortex has a role in creating personality.

The importance of the cortex was corroborated in another study conducted by University of Heidelberg psychologists. There, criminal offenders’ brains were also analyzed for changes in brain volume, and those exhibiting psychopathic traits as well as antisocial offenders with borderline personality disorder had reduced cortical area volumes [11]. Psychopathy can be attributed to factors beyond cortical volume, as it is also possible for personality to be drastically altered as a result of a force trauma event. For example, neurologists at the UCLA David Geffen School of Medicine were able to show that US veterans who had sustained blast force in battle were more likely to exhibit psychopathic behavior with increased neuroticism [12].

While brain structure is one facet that influences personality, recent research has also linked personality to genetics and hormones. A famous 1993 study conducted by molecular biologist Dean Hamer provided evidence that homosexuality was linked to a small DNA sequence at the tip of the X chromosome; since then, he has tied the human drive for novelty as well as anxiety to chromosomes 11 and 17, respectively [13]. Meanwhile, studies have shown that increased testosterone levels directly correlate to increased aggression, self-confidence, violence, and isolation [14]. Although theories are far from cohesive, we have made important strides in understanding the deep complexities of personality.

References:
1. John Markoff, “Obama Seeking to Boost Study of Human Brain,” New York Times, February 17, 2013, http://www.nytimes.com/2013/02/18/science/project-seeks-to-build-map-of-human-brain.html?pagewanted=all&_r=0.
2. Emily Underwood and Jocelyn Kaiser, “Brain Project Draws Presidential Interest,” Science Magazine, February 20, 2013, http://news.sciencemag.org/scienceinsider/2013/02/brain-project-draws-presidential.html.
3. “History of Personality Theory,” http://armchair_academic.homestead.com/HistoryPer.html.
4. “The History of Phrenology,” http://www.phrenology.org/intro.html.
5. “What is Phrenology?” http://psychology.about.com/od/historyofpsychology/f/phrenology.htm.
6. “The Big Five Personality Dimensions,” http://psychology.about.com/od/personalitydevelopment/a/bigfive.htm.
7. Colin G. DeYoung et al. “Testing Predictions From Personality Neuroscience,” Psychological Science 2010; 21:820-8.
8. “Brain Structures and Their Functions,” http://serendip.brynmawr.edu/bb/kinser/Structure1.html.
9. Colin Mahoney et al. Neuroanatomical profiles of personality change in frontotemporal lobar degeneration. The British Journal of Psychiatry 2011; 198: 365-372.
10. “What is the Brain Cortex?” http://www.onlineschools.org/library/what-is-the-brain-cortex/.
11. Katja Bertsch et al. Brain volumes differ between diagnostic groups of violent criminal offenders. European Archives of Psychiatry and Clinical Neuroscience 2013 (epub ahead of print). Accessed http://www.ncbi.nlm.nih.gov/pubmed/23381548.
12. Mario Mendez et al. Changes in personality after mild traumatic brain injury from primary blast vs. blunt forces. Brain Injury 2013; 27: 10-18.
13. J. Madeleine Nash, “The Personality Genes,” Time Magazine, June 24, 2001, http://www.time.com/time/magazine/article/0,9171,139036,00.html.
14. “Hormones, Sex and Personality Type,” http://www.darionardi.com/BulletinArt9.html.
Image Credits:
http://upload.wikimedia.org/wikipedia/commons/8/85/Cerebral_lobes.png .
http://farm4.static.flickr.com/3271/2816577131_6048d282d6_m.jpg

Cecilia Jiang is a second-year student at the University of Chicago majoring in the Biological Sciences, potentially with a specialization in Neuroscience. One of her interests include following significant scientific achievements in the news.