Article

The Neuroscience of Mammalian Associative Learning

Department of Psychology and Brain Research Institute, University of California-Los Angeles, Los Angeles, CA 90095-1563, USA.
Annual Review of Psychology (Impact Factor: 21.81). 02/2005; 56(1):207-34. DOI: 10.1146/annurev.psych.56.091103.070213
Source: PubMed

ABSTRACT

Mammalian associative learning is organized into separate anatomically defined functional systems. We illustrate the organization of two of these systems, Pavlovian fear conditioning and Pavlovian eyeblink conditioning, by describing studies using mutant mice, brain stimulation and recording, brain lesions and direct pharmacological manipulations of specific brain regions. The amygdala serves as the neuroanatomical hub of the former, whereas the cerebellum is the hub of the latter. Pathways that carry information about signals for biologically important events arrive at these hubs by circuitry that depends on stimulus modality and complexity. Within the amygdala and cerebellum, neural plasticity occurs because of convergence of these stimuli and the biologically important information they predict. This neural plasticity is the physical basis of associative memory formation, and although the intracellular mechanisms of plasticity within these structures share some similarities, they differ significantly. The last Annual Review of Psychology article to specifically tackle the question of mammalian associative learning ( Lavond et al. 1993 ) persuasively argued that identifiable "essential" circuits encode memories formed during associative learning. The next dozen years saw breathtaking progress not only in detailing those essential circuits but also in identifying the essential processes occurring at the synapses (e.g., Bi & Poo 2001, Martinez & Derrick 1996 ) and within the neurons (e.g., Malinow & Malenka 2002, Murthy & De Camilli 2003 ) that make up those circuits. In this chapter, we describe the orientation that the neuroscience of learning has taken and review some of the progress made within that orientation.

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    • "The CE is one main output region of the amygdala with projections to subcortical and brainstem areas. It coordinates defensive (fear) responses including freezing and endogenous opioid-mediated analgesia (periaqueductal gray, PAG), and startle reflex potentiation (nucleus reticularis pontis caudalis;Davis, 1992;Sah et al., 2003;Fanselow and Poulos, 2005;Pape and Paré, 2010). The CE is also connected to monoamine systems in the brain, including locus coeruleus (LC; noradrenaline, NA), dorsal/ventral striatum (dopamine, DA), and raphe nuclei [serotonin (5-hydroxytryptamine, 5-HT)]. "
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    ABSTRACT: Fear acquisition and extinction are valid models for the etiology and treatment of anxiety, trauma- and stressor-related disorders. These disorders are assumed to involve aversive learning under acute and/or chronic stress. Importantly, fear conditioning and stress share common neuronal circuits. The stress response involves multiple changes interacting in a time-dependent manner: (a) the fast first-wave stress response (with central actions of noradrenaline, dopamine, serotonin, corticotropin-releasing hormone, plus increased sympathetic tone and peripheral catecholamine release) and (b) the second-wave stress response (with peripheral release of glucocorticoids after activation of the hypothalamus-pituitary-adrenocortical axis). Control of fear during extinction is also sensitive to these stress-response mediators. In the present review, we will thus examine current animal and human data, addressing the role of stress and single stress-response mediators for successful acquisition, consolidation and recall of fear extinction. We report studies using pharmacological manipulations targeting a number of stress-related neurotransmitters and neuromodulators (monoamines, opioids, endocannabinoids, neuropeptide Y, oxytocin, glucocorticoids) and behavioral stress induction. As anxiety, trauma- and stressor-related disorders are more common in women, recent research focuses on female sex hormones and identifies a potential role for estradiol in fear extinction. We will thus summarize animal and human data on the role of estradiol and explore possible interactions with stress or stress-response mediators in extinction. This also aims at identifying time-windows of enhanced (or reduced) sensitivity for fear extinction, and thus also for successful exposure therapy.
    Full-text · Article · Jan 2016 · Frontiers in Behavioral Neuroscience
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    • "Pavlovian conditioned stimuli (CS; e.g., tone) produce defensive behaviors such as freezing after being paired with an aversive unconditioned stimulus (US; e.g., footshock; Pavlov, 1927). This form of learning depends on neural connections in the amygdala (LeDoux, 2000; Goosens and Maren, 2001; Fanselow and Poulos, 2005; Maren, 2005; Herry and Johansen, 2014; Lüthi and Lüscher, 2014; Janak and Tye, 2015). While the term Pavlovian fear conditioning is commonly used to describe this procedure, it implies that the subjective mental state of fear is being acquired. "
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    ABSTRACT: Two studies explored the role of the amygdala in response modulation by an aversive conditioned stimulus (CS) in rats. Experiment 1 investigated the role of amygdala circuitry in conditioned suppression using a paradigm in which licking for sucrose was inhibited by a tone CS that had been previously paired with footshock. Electrolytic lesions of the lateral amygdala (LA) impaired suppression relative to sham-operated animals, and produced the same pattern of results when applied to central amygdala. In addition, disconnection of the lateral and central amygdala, by unilateral lesion of each on opposite sides of the brain, also impaired suppression relative to control subjects that received lesions of both areas on the same side. In each case, lesions were placed following Pavlovian conditioning and instrumental training, but before testing. This procedure produced within-subjects measures of the effects of lesion on freezing and between-group comparisons for the effects on suppression. Experiment 2 extended this analysis to a task where an aversive CS suppressed shuttling responses that had been previously food reinforced and also found effects of bilateral lesions of the central amygdala in a pre-post design. Together, these studies demonstrate that connections between the lateral and central amygdala constitute a serial circuit involved in processing aversive Pavlovian stimuli, and add to a growing body of findings implicating central amygdala in the modulation of instrumental behavior.
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    • "Both of these types of learning involve the interaction between the hippocampus and the amygdala (e.g. Kim & Fanselow 1992; Phelps & LeDoux 2005; Phillips & LeDoux 1992; Selden et al. 1991). Once established, the aversive response to the CS may be decreased in strength through repeated presentation of the CS without the US, an active learning process referred to as extinction (Bouton et al. 2006). "
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