Summary: Memory encoding processes that shape later choices begin in the basolateral amygdala. That structure then drives lasting cellular changes in the nucleus accumbens that allow learned stimulus–reward associations to bias future decisions.
Source: University of New South Wales
Learned links between cues and reward — the same psychological process that gives brands their emotional pull — strongly influence our choices. New research from UNSW Sydney identifies how these associations are encoded in the brain to guide future decisions.
Researchers at the Decision Neuroscience Laboratory at UNSW Sydney have described a previously unrecognized memory mechanism that explains how Pavlovian or predictive learning can steer goal-directed behavior later in life. Although the experiments were performed in rats, the neural principles revealed are highly relevant to human decision-making.
Scientia Professor Bernard Balleine, Director of the Decision Neuroscience Laboratory and co-senior author of the study, compares this process to the cumulative effect of advertising. “When we choose between similar, similarly priced products, what often tips the balance are brand-related images and cues that we have learned to associate with value,” he says. “Over time these cues build emotional connections that can sway decisions long after the initial exposure.”
To investigate how these associations are stored and later influence choice, the team trained rats to link distinct sounds with different food rewards (for example, a long tone predicting a pellet and a rapid click predicting sugar). After training, hearing a specific cue was sufficient to trigger anticipation and actions directed toward the associated reward, such as approaching the lever that yields sugar.
Rats are commonly used in decision-making research because they share many behavioral and neural features with humans: they are omnivorous, social, and constantly predicting where and how to obtain valued outcomes. These shared traits make rodent models well suited to reveal the brain circuits underpinning core psychological capacities.
Cellular memories
Detailed neural analyses showed that encoding of predictive learning begins in the basolateral amygdala (BLA), a region long associated with emotional learning and memory. The BLA then drives a lasting cellular change in the nucleus accumbens shell (NAc-S) that serves as the memory substrate allowing those learned predictions to influence later choices.
Specifically, predictive learning promotes accumulation of delta opioid receptors (DOPRs) on the somatic membrane of cholinergic interneurons within the NAc-S. These receptors are members of the G protein–coupled receptor (GPCR) family and, in this case, their increased membrane expression is triggered by the predictive cue itself — not only by the reward. The DOPR build-up occurs during learning, persists for weeks, and is required for stimulus–reward memories to exert their influence on choices between alternative actions.
“Those receptors effectively bias our behavior in situations where a learned predictor of reward is present,” Prof. Balleine explains. “The accumulation of DOPRs on NAc-S cholinergic interneurons produces a physical, long-lasting change that enables a stimulus to guide the selection and execution of specific actions.”
The researchers also identified an upstream mechanism: the BLA influences DOPR accumulation via modulation of substance P release from D1-expressing spiny projection neurons in the NAc-S. Although DOPR accumulation is not required for forming the basic stimulus–reward association, it is necessary for that association to later alter the choice between competing actions. This constitutes the first evidence of a GPCR-mediated form of memory that links predictive learning to decision-making.
“Up until now, it was thought that these decision-making processes required a far broader set of structures and circuits.”
The science of decision-making
Prof. Balleine and colleagues plan to expand this line of work by examining the role of other GPCR families in encoding psychological processes and by tracking how DOPR expression is maintained over time. Each new discovery from the Decision Neuroscience Laboratory clarifies how complex brain processes control the decisions we make: how we select among actions to obtain desired outcomes and avoid those we dislike or fear.
The team’s broader research program includes investigations into the circuits and memory processes that control voluntary actions, with the aim of informing treatments for decision-making impairments that can occur with ageing and neurological disorders. In 2019 Prof. Balleine received an Australian Research Council Discovery Project Grant to pursue related questions about the neural control of goal-directed behavior.
About this neuroscience research article
Source: University of New South Wales
Media contacts: Sherry Landow – University of New South Wales
Image source: Image adapted from the University of New South Wales news release.
Original research: Closed access. Article title: “Basolateral Amygdala Drives a GPCR-Mediated Striatal Memory Necessary for Predictive Learning to Influence Choice” by Bernard Balleine et al., published in Neuron. DOI: 10.1016/j.neuron.2020.03.007
Abstract (research highlights)
• The basolateral amygdala encodes predictive learning and drives accumulation of DOPRs on NAc-S cholinergic interneurons.
• The BLA mediates DOPR accumulation via substance P release from D1-expressing spiny projection neurons in the NAc-S.
• DOPR accumulation reveals how predictive learning can influence choice between actions.
• DOPR accumulation on NAc-S cholinergic interneurons represents a novel, GPCR-based form of memory.
Predictive learning powerfully biases choice between instrumental actions, but how such learning is encoded stably enough to affect choices long after learning has been unclear. This study shows that the basolateral amygdala establishes a durable striatal memory by promoting delta opioid receptor accumulation on cholinergic interneurons in the nucleus accumbens shell. While these DOPR changes are not required for forming the initial stimulus–reward association, they are necessary for that association to later guide selection and execution of specific actions. These findings reveal a new GPCR-mediated memory mechanism by which predictive learning exerts long-term influence on decision-making.