A neurocognitive approach to understanding the neurobiology of addiction

Abstract

Recent concepts of addiction to drugs (e.g. cocaine) and non-drugs (e.g. gambling) have proposed that these behaviors are the product of an imbalance between three separate, but interacting, neural systems: an impulsive, largely amygdala-striatum dependent, neural system that promotes automatic, habitual and salient behaviors; a reflective, mainly prefrontal cortex dependent, neural system for decision-making, forecasting the future consequences of a behavior, and inhibitory control; and the insula that integrates interoception states into conscious feelings and into decision-making processes that are involved in uncertain risk and reward. These systems account for poor decision-making (i.e. prioritizing short-term consequences of a decisional option) leading to more elevated addiction risk and relapse. This article provides neural evidence for this three-systems neural model of addiction.

Figure 1

A schematic neurological model illustrating a proposed functional role for three key neural systems in addiction: (1) The amygdala-striatal neural system, which we have termed the “impulsive system”, excites the traditional reward system involved in the execution of motivational states to seek drugs, such as the ventral striatum/nucleus accumbens and the mesolimbic dopamine system (highlighted in red); (2) The mesial orbitofrontal/ventromedial prefrontal cortex (OFC/VMPC) is a key structure in a neural system we have termed the “reflective system”, which forecasts the future consequences of a behavior such as seeking drugs; (3) The proposed functional role of the insula is highlighted in green. Incentive stimuli (e.g., drug cues) generate motivation in the animal (or human) and instigate approach responses in relation to themselves through the “impulsive system”. However, internal factors associated with deprivation states (such as withdrawal) are viewed as a “gate” that determines how effective the incentive input is in exciting the motivational circuits that “pull” and “steer” the animal (or human) towards the appropriate goal object. This process, we propose, is dependent on the insula. Feedback loops arising from the body, reflecting the status of the viscera and homeostasis, and mediated through the insula, will adjust the strengths of the conflicting signals, thereby sensitizing the impulsive system, and potentially over-riding the inhibitory control of the reflective system. An additional possibility is that insula signals may subvert the decision-making processes of the reflective system into formulating plans for action to seek and procure drugs.