The nucleus accumbens as a nexus between values and goals in goal-directed behavior: a review and a new hypothesis

Abstract

Goal-directed behavior is a fundamental means by which animals can flexibly solve the challenges posed by variable external and internal conditions. Recently, the processes and brain mechanisms underlying such behavior have been extensively studied from behavioral, neuroscientific and computational perspectives. This research has highlighted the processes underlying goal-directed behavior and associated brain systems including prefrontal cortex, basal ganglia and, in particular therein, the nucleus accumbens (NAcc). This paper focusses on one particular process at the core of goal-directed behavior: how motivational value is assigned to goals on the basis of internal states and environmental stimuli, and how this supports goal selection processes. Various biological and computational accounts have been given of this problem and of related multiple neural and behavior phenomena, but we still lack an integrated hypothesis on the generation and use of value for goal selection. This paper proposes an hypothesis that aims to solve this problem and is based on this key elements: (a) amygdala and hippocampus establish the motivational value of stimuli and goals; (b) prefrontal cortex encodes various types of action outcomes; (c) NAcc integrates different sources of value, representing them in terms of a common currency with the aid of dopamine, and thereby plays a major role in selecting action outcomes within prefrontal cortex. The “goals” pursued by the organism are the outcomes selected by these processes. The hypothesis is developed in the context of a critical review of relevant biological and computational literature which offer it support. The paper shows how the hypothesis has the potential to integrate existing interpretations of motivational value and goal selection.

Frequency of Cocaine Self-Administration Influences Drug Seeking in the Rat: Optogenetic Evidence for a Role of the Prelimbic Cortex

“…Functional connectivity between the BLA and NAc core is known to be implicated in processing information about emotional or motivational significance and in mediating Pavlovian and instrumental incentive processes (Shiflett and Balleine, 2010). In contrast, connectivity between the PL and NAc core could contribute to reward-associated action selection (Mannella et al, 2013) by integrating learned contingencies that mediate instrumental performance and ultimately behavioral control.…”

Habitual control of goal selection in humans

“…The possibility of habitual control over goal selection complements several existing models in RL and psychology (11)(12)(13). Some RL algorithms have implemented model-free control over hierarchical goal selection, and with promising results (12).…”

“…Thus, the implementation of the abstract actions is an excellent candidate for planning. This example illustrates the utility of nesting elements of both habits and plans in a hierarchy of behavioral control (11)(12)(13).…”

Beyond Machine Learning: Autonomous Learning

“…Indeed an important aspect of autonomous decision making is to be able to adapt the behavior as a compromise between external goals (what should be searched and avoided) and internal goals (what are the current needs), whereas classical reinforcement learning generally relies on optimizing a simple scalar representing an abstract reward, artificially given in some situations. To progress in that aim, it is fundamental to better understand how internal and external goals (motivational and emotional cues) are combined in decision making (Zahm, 1999;Mannella et al, 2013;Kolling et al, 2016).…”