Dual-learning systems under stress

Abstract: There is mounting evidence in psychology, neuroscience and behavioral economics to support the notion that human behavior is governed by dual-learning systems, namely, reflective, “cognitive” or reflexive, “habitual” system. The former one is performed automatically, responds quickly and does not consume cognitive resources. The latter one responds slowly and consumes more cognitive resources, but it is also more flexible and sensitive to the changes in the external environment. Both of these learning systems exist in parallel and compete with each other to jointly influence individual's mind and behavior. A widely concerned question in recent years is which system exerts dominant control over specific behavior and what factors determine whether reflective or reflexive system governs behavior. Over the past decades, researchers used navigation learning task, probabilistic classification learning or instrumental learning task and associated computational models to explore the changes of multiple learning systems under acute and chronic stress at both behavioral and neural levels. By reviewing these studies, we summarize the psychophysiological mechanism underlying the stress-induced bias toward habitual behavior, and reinterpret the causal relationship between this shift and drug addiction. Existing research shows that noradrenaline and glucocorticoids act through mineralocorticoid receptors and exert interactive impact on brain regions that subserve dual-learning systems, which is orchestrated by the amygdala. Future studies need to focus on the modulatory role of genetic differences in the effects of stress on learning, and use a variety of technical methods to elucidate its neuroendocrine basis.