Lesions of dorsolateral striatum preserve outcome expectancy but disrupt habit formation in instrumental learning

As animals learn novel behavioural responses, performance is maintained by two dissociable influences. Initial responding is goal-directed and under voluntary control, but overtraining of the same response routine leads to behavioural autonomy and the development of habits that are no longer voluntary or goal-directed. Rats normally show goal-directed performance after limited training, indexed by sensitivity to changes in the value of reward, but this sensitivity to goal value is lost with extended training. Rats with selective lesions of the prelimbic medial prefrontal cortex showed no sensitivity to goal value after either limited or extended training, whereas rats with lesions of the infralimbic region of the medial prefrontal cortex showed the opposite pattern of deficit, a marked sensitivity to goal value after both limited and extended training. This double-dissociation suggests that the prelimbic region is responsible for voluntary response performance and the infralimbic cortex mediates the incremental ability of extended training to override this goal-directed behaviour.

This study investigated the respective roles of the hippocampus, the amygdala, and the dorsal striatum in learning and memory. A standard set of experimental conditions for studying the effects of lesions to the three brain areas using an 8-arm radial maze was used: a win-shift version, a conditioned cue preference (CCP) version, and a win-stay version. Damage to the hippocampal system impaired acquisition of the win-shift task but not the CCP or win-stay tasks. Damage to the lateral amygdala impaired acquisition of the CCP task but not the win-shift or win-stay tasks. Damage to the dorsal striatum impaired acquisition of the win-stay task but not the win-shift or CCP tasks. These results are consistent with the hypothesis that the mammalian brain may be capable of acquiring different kinds of information with different, more-or-less independent neural systems. A neural system that includes the hippocampus may acquire information about the relationships among stimuli and events. A neural system that includes the amygdala may mediate the rapid acquisition of behaviors based on biologically significant events with affective properties. A neural system that includes the dorsal striatum may mediate the formation of reinforced stimulus-response associations.