This extensive dopaminergic projection system is the critical reward circuitry, whose function encompasses all aspects of reward. It has been hypothesized that the prefrontal cortex codes for the anticipation of reward and it drives reward-seeking behavior. These specific circuitries include the anterior cingulate/ventral striatal regions. The anterior cingulate, also known as the medial frontal circuitry system, appears to play a particularly important role in monitoring behavior with respect to anticipated or expected rewards [186]. Anticipation is an inherent design characteristic of the brain [187], which functions by anticipating or predicting behavioral outcomes. It makes choices and decisions on the basis of what it expects the outcomes of those behaviors will be [117, 144]. These outcomes are based on reward probabilities. The ACC–basal ganglia–thalamic modulation loop seems specialized to monitor how well, how smoothly, or how poorly or unexpectedly things are going and to recruit other adaptive control and adjustment mechanisms as they are required. The orbitofrontal and medial frontal cortex projection systems are related to certain types of consummatory reward or reinforcement, which are active with the actual enjoyment the individual experiences [187]. The ventral striatum becomes highly active with the anticipation of reward and particularly under conditions of high certainty, when the individual is pretty sure that something “positive” will happen, though it also remains active during periods of consumption [188]. This extended basal forebrain region is extremely rich in dopamine [189–191] and regulates a diverse set of behaviors, including the control of movement; the modulation of desire, motivation, and cognition [192]; attention; different aspects of reward and mood; and certain appetitive drives. How this instrumental reward system operates consistently in mediating this wide range of functions will be discussed in Volume II.

The focusing and integrative functions of the frontal–striatal system play a dominant role in a model of brain functioning that is based on continuous sensorimotor interaction with the environment. The direct and indirect pathways of the basal ganglia, which are differentially modulated by dopamine, mediate reinforcement learning. Activity within the direct pathway leads to positive reinforcement and associations, while activity within the indirect pathway leads to negative outcomes and their avoidance. In this way, the frontal–striatal system learns what it should do and what it should not do depending upon the stimulus context. The neural systems governing behaviors that are strongly and repeatedly coactivated are strengthened. The basal ganglia use stimulus context and its generalizability to reliably release actions that have a high probability of generating a positive outcome and to avoid those behaviors that have become associated with negative outcomes. As proposed by Cockburn and Frank, as stimulus–response representations in the sensory cortices and motor regions coactivate, the strength between the cortical regions that specify the parameters for the behavior and its execution also increases [174]. This generates the formation of habits, which are retained in the neocortex and become independent of the basal ganglia over time [193, 194]. The hyperdirect pathway allows for the cessation of behavior in ambiguous circumstances where several candidate behaviors are possible and/or when new behaviors have to be generated. The hyperdirect pathway essentially prevents impulsive, premature responding when the most appropriate course of action needs to be formulated and decided upon. These processes support a dual-tiered system of behavioral control, characterized by automatic, habitual behaviors that alternate with episodes of higher-order thinking.