The roles of the nucleus accumbens core, dorsomedial striatum, and dorsolateral striatum in learning: Performance and extinction of Pavlovian fear-conditioned responses and instrumental avoidance responses

摘要

During dangerous situations animals express species-specific fear behaviors. Freezing, fleeing (escape) and fighting are common unconditioned fear responses in rodents (Blanchard & Blanchard, 1989; Martinez, Oliveira, Macedo, Molina, & Brandao, 2008). Pavlovian conditioning significantly increases the chances of survival by allowing animals to anticipate a threatening event and respond preemptively (Blanchard & Blanchard, 1969; Fanselow & Bolles, 1979). Animals can also learn responses that are instrumental in avoiding danger (Bolles, 1970) and can learn conditioned avoidance responses (CARs) when responding to a Pavlovian stimulus in order to avoid a threatening event that would otherwise follow (Maia, 2010; Mowrer, 1956). Unconditioned fear responses, Pavlovian conditioned fear responses and CARs are also critical for human beings to deal with situations involving physical risks or aversive social challenges, and deficits in these processes are implicated in anxiety disorders (Deakin & Graeff, 1991; Graybiel, 2008; Levita, Hoskin, & Champi, 2012; Lovibond, Chen, Mitchell, & Weidemann, 2013).CARs depend on both Pavlovian and instrumental conditioning (Maia, 2010; Mowrer, 1956). In order to know when to act in order to avoid an aversive event^ignaled by a cue, the subject must first learn that the specific cue predicts the aversive event. Knowing this, one can choose an instrumental action to avoid the announced aversive event. In rodents, such learning is modeled by the 2-way active avoidance task in which rats can avoid a cued (announced) footshock by crossing to the opposite side of a shuttle box. Performance of this task depends on selecting this action in response to a specific predictive stimulus.