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    • br Amygdala striatal interactions in maturity The

    2018-11-03


    Amygdala-striatal interactions in maturity The unidirectional glutamatergic projections from the BLA to the ventral striatum (Everitt et al., 1991; Groenewegen et al., 1999; Robbins et al., 1989) facilitate the ventral striatum’s role as an interfacing region able to translate evaluative signals into action. The basolateral amygdala encodes the sensory and affective properties of stimuli and outcomes (i.e., value) learned via Pavlovian or instrumental conditioning processes, which are then relayed to the ventral striatum to translate into value-based actions (e.g., pursue, avoid) (Everitt et al., 1991; Groenewegen et al., 1999; Hart et al., 2013; Robbins et al., 1989); thus, amygdala-ventral striatal connections may be critical for learning and updating stimulus value. We do note that the basolateral amygdala also projects to the dorsal striatum in rodents (Hart et al., 2013) and non-human primates (Cho et al., 2013), which may facilitate response-outcome learning (Balleine et al., 2007; Hart et al., 2013). The rodent literature provides a useful vitamin d receptor from which to examine the nature of amygdala-striatal interactions, particularly given that work on this in humans is limited. Studies of reward devaluation (Balleine and Dickinson, 1998; Yin et al., 2004) indicate that motivated responding for rewards can be influenced or controlled by representations of a response and a reward, and this process appears dependent upon the relationship between the BLA and NAcc. Reward devaluation involves either allowing an animal to consume a valued stimulus (i.e., food reward) to satiety or conditioning a previously rewarding stimulus with an aversive outcome (i.e., poison), and then testing in extinction whether the animal continues to choose that stimulus. Indeed, lesioning BLA-NAcc core projections eliminates reward devaluation effects, resulting in continued pursuit of devalued outcomes. BLA-NAcc shell lesions, on the other hand, leave intact the ability to detect changes in outcome value (Shiflett and Balleine, 2010). Studies involving a phenomenon known as Pavlovian-to-instrumental transfer (PIT) provide additional insight into the nature of amygdalostriatal interactions. PIT studies measure a process by which instrumental approach or avoidance of incentives are mediated by Pavlovian associations between an environmental stimulus and the incentive (Balleine and Dickinson, 1998; Cardinal and Everitt, 2004 see also Lewis et al., 2013). Testing PIT in the laboratory involves classically conditioning organisms to associate a stimulus with a rewarding (or aversive) outcome and later testing in extinction if the organism increases instrumental responding for an incentive in the presence of only the classically conditioned cue (specific PIT) or in the presence of any cue (general PIT) (Balleine and Dickinson, 1998; Lewis et al., 2013). BLA-NAcc interactions are critical to both types of PIT (Corbit and Balleine, 2005), such that lesioning BLA-NAcc shell projections impairs specific PIT while lesioning CeA-NAcc core projections impair general PIT (Corbit and Balleine, 2011). This dichotomy suggests that the NAcc shell may be important for inhibiting responding to stimuli that were not paired with a reinforcing outcome (Corbit and Balleine, 2011). Reward devaluation and PIT studies thus highlight the importance of amygdalostriatal interactions in affective learning that may mimic real-life conditions, in which we come to associate certain behaviors (e.g., eating, drinking) with specific contexts (e.g., specific groups of people) or in which we have to rapidly learn about changing environmental contingencies. Amygdalostriatal interactions originate from the amygdala. Recording of local field potentials (low frequency electrical signal fluctuation in a neuronal population likely reflecting synaptic input; (van der Meer, 2010)) from the basolateral amygdala and striatum in cats has revealed spontaneous preferential coupling of amygdala and striatal gamma oscillations, which is induced by the BLA (Popescu et al., 2009). Gamma oscillations are generally thought to be important for a variety of cognitive processes (van der Meer, 2010), and for broader homeostatic maintenance (Merker, 2013). Amygdalostriatal coupling was associated with improved reward-learning performance (Popescu et al., 2009). Amygdala-induced NAcc reward-related responses are further dependent upon glutamatergic BLA to NAcc projections (though see also Britt et al., 2012; Stuber et al., 2011), and optogenetic inactivation of the BLA reduces NAcc neural firing to reward predicting stimuli (Ambroggi et al., 2008). Taken together, amygdalostriatal interactions in affective valuation and learning appear based on excitatory amygdala-based signals sent to the ventral striatum, which then facilitates value-based decisions/actions.