Chapter 20: Personality Neuroscience and Individual Differences

Personality Neuroscience and Individual Differences explains that personality psychology has shifted focus from merely describing how people differ to explaining why they differ, a transition facilitated by advancements in neuroscientific tools such as neuroimaging, molecular genetics, and electrophysiological techniques. The dominant framework for organizing these individual differences is the Five-Factor Model, or Big Five, which categorizes almost all traits into five broad domains: Extraversion, Neuroticism, Agreeableness, Conscientiousness, and Openness/Intellect. These traits are known to be substantially heritable and demonstrate genetic universality across diverse populations. Core theories that relate personality to neurobiology include Eysenck's arousal-based model, Gray’s Reinforcement Sensitivity Theory (RST)—which posits that Neuroticism and Extraversion are determined by the Behavioral Inhibition System (BIS) and Behavioral Approach System (BAS), respectively—and dimensional models proposed by theorists such as Zuckerman, Cloninger, and Depue, all of which link traits to specific functional brain systems and neuromodulators. Behavior genetic analysis reveals a higher-order structure among the Big Five, grouping them into two meta-traits: Stability (or alpha, encompassing low Neuroticism, Agreeableness, and Conscientiousness), broadly linked to the modulatory function of serotonin, which regulates impulse control; and Plasticity (or beta, encompassing Extraversion and Openness/Intellect), associated with dopamine, which governs exploratory behavior and cognitive flexibility. At the individual trait level, Extraversion is linked to reward sensitivity, the BAS, and dopaminergic circuitry in areas like the nucleus accumbens. Neuroticism is associated with threat sensitivity, the FFFS/BIS systems, lower serotonergic function, and activity in regions like the amygdala and anterior cingulate. Agreeableness reflects prosociality and social stability, involving brain systems for empathy and theory of mind, such as the mirror neuron system and medial prefrontal cortex, and is modulated by substances like oxytocin and testosterone. Conscientiousness, tied to self-control and motivational stability, relies on inhibitory serotonergic function and high voluntary control capacity in the prefrontal cortex, potentially related to glucose metabolism. Finally, Openness/Intellect is strongly correlated with cognitive flexibility, fluid intelligence, and working memory performance, functions largely supported by the dopaminergic modulation of the lateral prefrontal cortex. The integration of these findings offers a promising path toward developing psychobiological models that can explain the entire hierarchy of personality structure.