The amygdala central nucleus: a new region implicated in habit learning.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Lingawi and Balleine The mechanisms underlying instrumental conditioning have been a rich source of experimental inquiry. Perhaps one of the most influential findings has been the transition from goal-directed, outcome-guided responding early in training to habitual, stimulus-response behavior following extended training of the instrumental response (Adams, 1982). To assess which strategy is being used, outcome devaluation procedures have proven useful. In these procedures, the outcome is devalued either through selective satiation or pairing with lithium chloride (LiCl) injections that subsequently induce gastric malaise; instrumental responding on the manipulandum that had been trained to yield the outcome is then assessed, typically in extinction. Instrumental responding that reflects sensitivity to devaluation indicates goal-directed action, whereas instrumental responding that is insensitive to devaluation demonstrates habitual behavior. This basic paradigm has been used extensively in recent years to delineate the neural circuitry important for these two classes of behavior. From such studies, regions of the amygdala, dorsal striatum, and prefrontal cortex have been identified as critical neural substrates of these behavioral processes (Balleine et al. Neuroscience by Lingawi and Balleine (2012) builds upon this work and furthers our understanding of the neural circuits underlying habitual instrumental behavior. Using the methodology outlined above, Lingawi and Balleine (2012) identified the anterior portion of the amygdala central nucleus (aCeN) as a necessary brain region for the acquisition of habits. All rats were overtrained on a lever-press response and, thereafter, the outcome was devalued using a conditioned taste-aversion procedure involving injections of LiCl. When tested in extinction, rats with bilateral sham lesions or lesions of the posterior part of the amygdala central nucleus showed no effect of devaluation; that is, these rats displayed a response pattern that did not reflect the current value of the outcome. Habitual responding in these animals, then, was unper-turbed. By contrast, rats with bilateral lesions of the aCeN maintained sensitivity to devaluation even after instrumental over-training, indicated by responding that was determined by the current value of the outcome. Thus, habitual responding in these animals was impaired. Moreover, Lingawi and Balleine (2012) showed that interaction of the aCeN with the dorsolateral …