I have always been fascinated by the neurobiological basis of personality types. This post will be followed by more on the neural basis of personality.
The Psychobiological basis of personality
Early studies on the correlations between personality and biology were largely centered on the construct of arousability, or the degree to which people respond to a particular stimulus. The measurement of excitatory or inhibitory reactions in our physiology has been done at many levels and with ever better levels of sophistication for decades. The primary method for measuring arousability was to conduct electrophysiological research (DeYoung & Gray, 2009). Early work from Ivan Pavlov was especially critical in that area (Pavlov, 1927) .
Understanding the way our nervous system works is critical in order to link biology and personality factors. There are three anatomical subdivisions which control and monitor the way we respond in any given situation: the central nervous system (CNS), the peripheral nervous system (PNS), and the autonomic nervous system (ANS). The CNS includes the brain and the spinal cord. It is like the CEO of our nervous system. The PNS is a network of nerves which relay information between the brain and the different parts of the body. The ANS shares some of the same network of nerves that are used by the CNS and the PNS but it basically works on autopilot to regulate critical functions that maintain our state of homeostasis. For instance, the ANS controls respiration, digestion, heart rate, temperature, sweating, etc. The ANS is further divided into two branches: the sympathetic (SNS) and the parasympathetic (PSNS). The SNS is able to hijack the resources of our entire body to address immediate situations that are critical to our survival. The “fight or flight” response is a typical example. On the other hand, the PSNS is in charge of keeping or restoring the body to a state of balance.
Changes in the ANS have been the subject of many personality studies because they signal important disruptions or tactical changes in critical affective, cognitive and behavioral functions (Mendes, 2009). Because the speed at which the ANS reacts is below our awareness, it may also help predict our conscious behavior (Bechara, Damasio, Tranel, & Damasio, 1997). The most commonly used methods to study the relationships between personality traits and the ANS have been electrodermal, cardiovascular, blood pressure, and muscle tension.
Electrodermal activity (EDA) is designed to measure the response of eccrine glands, which are the sweats glands found in virtually all of our skin and which are most numerous in the palms of our hands and the soles of our feet. These glands are very sensitive to external and internal stimuli. EDA is calculated by measuring the variation of a constant electrical current passing through the skin. The more active the glands are, the more skin conduction (SC) is affected by the stimulus. While EDA appears somewhat basic, some important findings on personality have been revealed using it. One study on emotional disclosure for instance measured that people who have a disposition to disclose traumatic events from their lives show less ANS response as measured by lower SC activation than low disclosers (Pennebaker, Hughes, & O'Heeron, 1987).
The cardiovascular system (CV) includes the heart and the vessels through which blood is delivered. Changes in CV provide important clues on heart rate variability (HRV) and vagal tone. Vagal activity directly correlates to how the PNS responds; therefore it is an important measure of how much an individual is able or is predisposed to maintain a state of homeostasis. Many studies confirm that there is a relationship between emotional styles and vagal tone (Gramzow, Willard, & Mendes, 2008; Porges, 2007).
Blood pressure (BP) is used to measure SNS responses to common stimuli like stress, threat or increased cognitive demands. Such responses can be mediated differently by people with varying personalities. Social psychologists have demonstrated that BP can be a good index to a****s people’s capacity or disposition to sustain effort while performing specific tasks (Wright & Kirby, 2003).
Muscle tension is measured by electromyography (EMG), a tool to record electrical activity produced by the contractions of muscles. The most popular use of EMG is to record action potentials generated by facial expressions (Hesse, 2009). Facial EMG has been used in numerous studies to measure many affective states. It is considered to have high resolution because many expressions can be recorded which are not visible because they are too fast for the human eye to notice. Considering that the universality of basic facial expressions has been long established (Darwin, 1872; Ekman, 1971), facial EMG has shown to be often more reliable than self-reports, especially to measure attention and fatigue.
While the methods I just reviewed offer valuable tools to a****s and measure the physiological manifestations of personality traits in many situations, they provide limited explanations of the complex mechanism underlying such responses. This can only be achieved by looking at the commander in chief of the nervous system: the brain (to be continued).
Bechara, A., Damasio, H., Tranel, D., & Damasio, A. R. (1997). Deciding advantageously before knowing the advantageous strategy. Science(275), 1293-1294.
Darwin, C. (1872). The expression of the emotions in man and animals. London, England: John Murray.
DeYoung, C. G., & Gray, J. R. (2009). Personality neuroscience: Explaining individual differences in affect, behavior, and cognition. In P. J. C. G. Matthews (Ed.), Cambridge handbook of personality (pp. 323-346). New York: Cambridge University Press.
Gramzow, R. H., Willard, G. B., & Mendes, W. B. (2008). Big tales and cool heads: GPA exaggeration is related to increased parasympathetic activation. Emotion, 8(1), 138-134.
Hesse, U. (2009). Facial EMG. In E. Harmon-Jones & J. S. Beer (Eds.), Methods in social
Mendes, W. B. (2009). A****sing autonomic nervous system activity. In Harmon-Jones & J. S. E. Beer (Eds.), Methods in social neuroscience (pp. 118-147). New York: The Guilford Press.
Pavlov, I. P. (1927). Conditional reflexes: An investigation of the physiological activity of the cerebral cortex. New York: Oxford University Press.
Pennebaker, J. W., Hughes, C. F., & O'Heeron, R. C. (1987). The psychobiology of confession: Linking inhibitory and psychosomatic processes. Journal of Personality and Social Psychology, 52(4), 781-793.
Wright, R. A., & Kirby, L. D. (2003). Cardiovascular correlates of challenge and threat appraisals: A critical examination of the biopsychosocial analysis. Personality and Social Psychology, 7(3), 216-233.
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