The amygdala and emotional modulation of competition between cognitive and habit memory

The basolateral amygdala (BLA) is implicated in the neurobiology of emotion, and can also modulate the cognitive and habit memory processes mediated by the hippocampus and dorsal striatum, respectively. In a dual-solution task that can be acquired using either hippocampus-dependent or dorsal striatal-dependent learning, peripheral or intra-BLA infusion of the anxiogenic alpha(2)-adrenoreceptor antagonist RS 79948 biases rats towards the use of habit learning. In view of evidence that anxiety can promote relapse into habitual and maladaptive human behaviors. understanding the mechanism(s) by which emotional arousal can influence the relative use of multiple memory systems may prove clinically relevant. Therefore, the present experiments examined whether intra-BLA infusions of RS 79948 bias rats towards the use of habit learning directly by enhancing dorsal striatal function, or indirectly by impairing hippocampal function. Adult male Long-Evans rats were trained in one of two single-solution water plus-maze tasks. One version required the use of hippocampus-dependent "place" learning. A second version required the use of dorsal striatal-dependent "response" learning, and hippocampal mnemonic processes have been shown to interfere with acquisition of this task. Post-training intra-BLA infusions of RS 79948 (1.0 mu g/0.5 mu l) impaired acquisition of place learning. In contrast, intra-BLA infusions of RS 79948 enhanced response learning. Intra-BLA infusion of RS 79948 also produced an anxiogenic behavioral profile in an elevated plus-maze at the same dose (1.0 mu g) that differentially influenced place and response learning. The findings suggest that intra-BLA infusion of an anxiogenic drug can influence the use of multiple memory systems by impairing hippocampus-dependent learning, thereby releasing habit memory from competing and/or inhibitory influences of cognitive memory. (C) 2008 Elsevier B.V. All rights reserved.