Anxiety, cognition, and habit: a multiple memory systems perspective.
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Consistent with a multiple systems approach to memory organization in the mammalian brain, numerous studies have differentiated the roles of the hippocampus and dorsal striatum in "cognitive" and "habit" learning and memory, respectively. Additional research indicates that activation of efferent projections of the basolateral amygdala (BLA), a brain region implicated in mammalian emotion, modulates memory processes occurring in other brain structures. The present brief review describes research designed to link these general concepts by examining the manner in which emotional state may influence the relative use of multiple memory systems. In a dual-solution plus-maze task that can be acquired using either hippocampus-dependent or dorsal striatal-dependent learning, acute pre-training or pre-retrieval emotional arousal (restraint stress/inescapable foot shock, exposure to the predator odor TMT, or peripheral injection of anixogenic drugs) biases rats towards the use of habit memory. Moreover, intra-BLA injection of anxiogenic drugs is sufficient to bias rats towards the use of dorsal striatal-dependent habit memory. In single-solution plus-maze tasks that require the use of either cognitive or habit learning, intra-BLA infusions of anxiogenic drugs result in a behavioral profile indicating an impairing effect on hippocampus-dependent memory that effectively produces enhanced habit learning by eliminating competitive interference between cognitive and habit memory systems. It is speculated that the predominant use of habit memory that can be produced by anxious and/or stressful emotional states may have implications for understanding the role of learning and memory processes in various human psychopathologies, including for example post-traumatic stress disorder and drug addiction.