Gray Matter Differentiation Between Two Subordinate Personality Traits of Extraversion: Enthusiasm and Assertiveness

Enthusiasm and assertiveness are two subordinate personality traits of extraversion. These traits reflect different aspects of extroversion and have distinct implications on mental health. Whereas enthusiasm predicts satisfaction in life and positive relationships, assertiveness predicts psychological distress and reduced social support. The neural basis of these subordinate traits is not well understood. To investigate brain regions where enthusiasm and assertiveness have diverging relationship with morphology, enthusiasm and assertiveness were regressed to gray matter volume (GMV) across the whole brain in a sample of 301 healthy individuals. A significant interaction was found between enthusiasm and assertiveness in the left angular gyrus (t(296) = 4.18, family wise error corrected, FWE p = .001 (cluster-level); Cluster size = 880 voxels). Larger GMV in this area was associated with more enthusiasm and less assertiveness. Our study emphasizes the value of separating extraversion into its subordinate traits when investigating associations to neuroanatomy.