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Typically the mammalian memory is divided into two main categories: deklarative memory, where the hippocampus plays a major role and non deklarative memory, which is divided into further sub-categories. One of these sub-categories is the procedural memory system, which is relevant for the acquisition of skills. Here the striatum plays a major role.
The aim of the present studies is to investigate the interplay of striatum and hippocampus in sequential learning (a further sub-category of procedural learning). The main method used is a rat version of the serial reaction time task (SRTT) which is commonly used to study sequential learning in humans. The effects of dorsal and ventral striatal 6-OHDA lesions and dorsal hippocampal ibotenic acid lesions on sequential behavior were tested.
Ventral striatal lesions had no effect on sequential learning, but on instrumental learning, dorsal striatal lesioned animals showed deficits in sequential learning as compared to sham operated and non operated controls. Dorsal hippocampal lesions surprisingly led to enhanced sequential learning and a higher degree of automated sequential behavior.
The found effects are explained by the multiple memory systems theory: both structures project to the prefrontal cortex for behavioral control. Since the information provided by the hippocampus to the prefrontal cortex is irrelevant in the SRTT, which requires highly automated procedural/sequential responses, hippocampal lesioned animals are more efficient in their performance.