AbstractDamage to the orbitofrontal cortex (OFC) can cause maladaptive social behavior, but the cognitive processes underlying these behavioral changes are still uncertain. Here, we tested whether patients with acquired OFC lesions show altered approach-avoidance tendencies to emotional facial expressions. Thirteen patients with focal OFC lesions and 31 age- and gender-matched healthy controls performed an implicit approach-avoidance task in which they either pushed or pulled a joystick depending on stimulus color. While controls avoided angry faces, OFC patients displayed an incongruent response pattern characterized by both increased approach and reduced avoidance of angry facial expressions. The approach bias was stronger in patients with higher self-reported impulsivity and disinhibition, and in those with larger lesions. Moreover, patients committed more errors in the task, which in turn was correlated with self-rated clinical impairment. We further used linear ballistic accumulator modelling to investigate latent parameters underlying approach-avoidance decisions. Controls displayed negative drift rates when approaching angry faces, whereas OFC lesions abolished this bias. In addition, OFC patients had weaker response drifts than controls during angry face avoidance. Finally, patients showed generally reduced variability in drift rates and shorter non-decision times, indicating impulsive and rigid decision-making. In sum, our findings suggest that OFC damage alters the pace of evidence accumulation in response to threat signals, eliminating a default, protective avoidant bias and facilitating dysfunctional approach behavior.Significance statementLesions in the orbitofrontal cortex (OFC) may alter social behavior, rendering individuals irritable or reckless. However, the precise cognitive mechanisms underlying these changes are unknown. We here examined whether OFC damage impacts how persons respond to social signals using a joystick-based task. Contrary to control participants, patients showed both increased approach to, and reduced avoidance of angry facial expressions, i.e. they were quicker to pull angry faces close and slower to push them away. Further analyses of reaction times revealed that OFC patients lack a default tendency against angry face approach, and that they show a slower decision build-up when avoiding angry faces. Thus, our findings suggest that OFC lesions reduce fearful responses to social threat signals.
Patients with Ventromedial Prefrontal Lesions Show an Implicit Approach Bias to Angry Faces