Callous-unemotional traits and pre-ejection period in response to reward.

Callous-unemotional (CU) traits have important utility in distinguishing individuals exhibiting more severe and persistent antisocial behavior, and our understanding of reward processing and CU traits contributes to behavioral modification. However, research on CU traits often investigated reward alongside punishment and examined solely on average reward reactivity, neglecting the reward response pattern over time such as habituation. This study assessed individuals' pre-ejection period (PEP), a sympathetic nervous system cardiac-linked biomarker with specificity to reward, during a simple reward task to investigate the association between CU traits and both average reward reactivity and reward response pattern over time (captured as responding trajectory). A heterogeneous sample of 126 adult males was recruited from a major metropolitan area in the US. Participants reported their CU traits using the Inventory of Callous-Unemotional Traits and completed a simple reward task while impedance cardiography and electrocardiogram were recorded to derive PEP. The results revealed no significant association between average PEP reward reactivity and CU traits. However, CU traits predicted both linear and quadratic slopes of the PEP reactivity trajectory: individuals with higher CU traits had slower habituation initially, followed by a rapid habituation in later blocks. Findings highlight the importance of modeling the trajectory of PEP reward response when studying CU traits. We discussed the implications of individuals with high CU traits having the responding pattern of slower initial habituation followed by rapid habituation to reward and the possible mechanisms.