Dorsolateral striatum implicated in the acquisition, but not expression, of immediate response learning in rodent submerged T-maze.

Animals can use multiple strategies when learning about, and navigating within, their environment. Typically, in the frequently-studied food-rewarded T-maze, rats initially adopt a flexible, hippocampal-dependent place strategy. However, as learning progresses, rats switch to an automatic, striatal-dependent response strategy (Packard & McGaugh, 1996). Interestingly, in a similar but aversively motivating water-submerged T-maze, rats exhibit the opposite behavioral pattern, initially adopting a response strategy but switching to a place strategy with extended training (Asem & Holland, 2013). Here, we examined the effects of transient lidocaine inactivation of the dorsolateral striatum (DLS) on rats' acquisition and expression of place and response strategies in the submerged T-maze. DLS inactivation prior to probe tests had no effect on rats' initial expression of a response strategy nor on their transition to the use of a place strategy with further training. Nevertheless, in a second experiment using the same rats, identical inactivation parameters significantly affected performance in an appetitively motivating positive control task, which required a response strategy. Furthermore, in a third experiment, DLS inactivation prior to early learning trials interfered with the acquisition of the response strategy in the submerged T-maze. These differences in DLS inactivation effects across appetitive and aversive tasks support the view that task motivation plays crucial roles in guiding learning, memory, and behavior. Additionally, differences in DLS inactivation effects between tests of acquisition and expression suggest that the DLS is required during early acquisition but not expression of the response learning strategy.