Amygdala and "emotional" modulation of the relative use of multiple memory systems.
The basolateral amygdala modulates the cognitive and habit memory processes mediated by the hippocampus and caudate nucleus, respectively. The present experiments used a plus-maze task that can be acquired using either hippocampus-dependent "place" learning or caudate-dependent "response" learning to examine whether peripheral or intra-basolateral amygdala injection of anxiogenic drugs would bias rats towards the use of a particular memory system. In Experiment 1, adult male Long-Evans rats were trained to swim from the same start point to an escape platform located in a consistent goal arm, and received pre-training peripheral injections of the alpha(2)-adrenoceptor antagonists yohimbine (2.5 or 5.0 mg/kg), RS 79948-197 (0.05, 0.1, or 0.2 mg/kg), or vehicle. On a drug-free probe trial from a novel start point administered 24h following acquisition, vehicle treated rats predominantly displayed hippocampus-dependent place learning, whereas rats previously treated with yohimbine (2.5, 5.0 mg/kg) or RS 79948-197 (0.1 mg/kg) predominantly displayed caudate-dependent response learning. In Experiment 2, rats receiving pre-training intra-basolateral amygdala infusions of RS 79948-197 (0.1 microg/0.5 microl) also predominantly displayed response learning on a drug-free probe trial. The findings indicate (1) peripheral injections of anxiogenic drugs can influence the relative use of multiple memory systems in a manner that favors caudate-dependent habit learning over hippocampus-dependent cognitive learning, and (2) intra-basolateral amygdala infusion of anxiogenic drugs is sufficient to produce this modulatory influence of emotional state on the use of multiple memory systems.
Packard
Mark G
MG
Department of Psychology, Texas A and M University, USA. gp@psyc.tamu.edu
Wingard
Jeffrey C
JC
D000317:Adrenergic alpha-Antagonists; D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001007:Anxiety / Q000139:chemically induced / Q000503:physiopathology*; D002421:Caudate Nucleus / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004924:Escape Reaction / Q000187:drug effects / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology*; D007263:Infusions, Parenteral; D007546:Isoquinolines; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology*; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D009287:Naphthyridines; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology; D051381:Rats; D020318:Rats, Long-Evans; D015016:Yohimbine
D000317:Adrenergic alpha-Antagonists; D007546:Isoquinolines; D009287:Naphthyridines; C104875:RS 79948-197; D015016:Yohimbine