Impulse Control Disorders in Neurological Settings

This chapter will argue that impulse control disorders, including addiction, are the product of an imbalance between two separate but interacting neural systems: (1) an impulsive amygdala-striatum–dependent neural system that promotes automatic and habitual behaviors and (2) a reflective prefrontal cortex–dependent neural system for decision making, forecasting the future consequences of a behavior, and inhibitory control. The reflective system controls the impulsive system via several mechanisms. However, this control is not absolute; hyperactivity within the impulsive system can override the reflective system. While most prior research has focused on the impulsive system (especially the ventral striatum and its mesolimbic dopamine projection) in promoting the motivation and drive to seek drugs, or on the reflective system (prefrontal cortex) and its mechanisms for decision making and impulse control, more recent evidence suggests that a largely overlooked structure, namely the insula, plays a key role in maintaining poor impulse control, including addiction. This review highlights the potential functional role the insula plays in addiction. We propose that the insula translates bottom-up, interoceptive signals into what subjectively may be experienced as an urge or craving, which in turn potentiates the activity of the impulsive system and/or weakens or hijacks the goal-driven cognitive resources that are needed for the normal operation of the reflective system.