Trait impulsiveness is related to smaller post‐commissural putamen volumes in males but not females

Impulsivity is considered a vulnerability trait for addiction. Recently, we found trait non‐planning impulsiveness measured with the Karolinska Scales of Personality was negatively correlated with dopamine D_2/3 receptor availability in the ventral striatum of healthy humans. While also observed in rodents, human studies have failed to find this association with other measures of trait impulsivity. We explored whether another rodent finding, reduced ventral striatum volume with greater impulsivity, could also be observed in humans using this scale. Non‐planning impulsiveness was measured in 52 healthy subjects (21 female; mean age: 33.06 ± 9.69) using the Karolinska Scales of Personality. Striatal subregion volumes, including the globus pallidus, were acquired using the Multiple Automatically Generated Templates (MAGeT‐Brain) algorithm. Although failing to support our a priori hypothesis, there was a significant sex interaction in the post‐commissural putamen with impulsiveness. Exploratory analyses revealed impulsiveness was negatively correlated with post‐commissural putamen volumes in males, but positively correlated in females. We replicated this finding in males in an increased sample (including all 52 previous subjects) who provided impulsiveness measured by the Temperament and Character Inventory (n = 73; 32 female; mean age: 33.48 ± 9.75). These correlations by sex were statistically different from one another, the main finding with the Kasolinksa Scales of Personality surviving correction for multiple comparisons. While impulsivity may be related to reduced ventral striatal D_2/3 receptors across sexes, males but not females may show significant reductions in post‐commissural putamen volume. These findings have important implications for understanding biological markers underlying sex differences in drug addiction vulnerability.