Dorsal hippocampal lesions boost performance in the rat sequential reaction time task

It is commonly accepted that the hippocampus plays a major role in declarative memory across species and that it is of particular relevance for spatial memory in rodents. However, the interplay between hippocampal function and nondeclarative memory systems, such as procedural stimulus‐response (S‐R)...

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Bibliographic Details
Published in:Hippocampus 2012-05, Vol.22 (5), p.1202-1214
Main Authors: Eckart, M.T., Huelse-Matia, M.C., Schwarting, R.K.W.
Format: Article
Language:English
Subjects:
Animals
dorsal hippocampus
Excitatory Amino Acid Agonists - adverse effects
exitotoxic lesions
Hippocampus - pathology
Hippocampus - physiopathology
Ibotenic Acid - adverse effects
Magnetic Resonance Imaging
Male
Memory Disorders - physiopathology
procedural learning
Rats
Rats, Wistar
Reaction Time
sequential learning
Serial Learning - physiology
SRTT
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Summary:It is commonly accepted that the hippocampus plays a major role in declarative memory across species and that it is of particular relevance for spatial memory in rodents. However, the interplay between hippocampal function and nondeclarative memory systems, such as procedural stimulus‐response (S‐R) or sequential learning, is less clear: depending on task requirements, an interaction, dissociation or interference between hippocampal function and other memory systems may occur. This study was conducted to investigate the influence of dorsal ibotenic hippocampal lesions on learning and performance of sequential behavior in a rat version of the serial reaction time task (SRTT). Magnetic resonance imaging (MRI) analyses of the lesions revealed a bilateral volume reduction of ∼ 46% (histological analyses: ∼59%) of the total hippocampus. They were largely confined to its dorsal part and led to an expected spatial memory deficits in an object place recognition test as compared to healthy controls, even though sham lesions had the same effect. Our earlier studies on sequential learning had revealed substantial impairments in case of dorsal striatal dopaminergic lesions. In the present study, however, hippocampal lesioned animals unexpectedly showed superior performance throughout SRTT testing and training as compared to controls, which resulted in a higher degree of subsequent automated sequential behavior. Thus, our data reveal the infrequent case where hippocampal lesions lead to long‐term improvements in test performance of a type of rather complex procedural behavior. One possible explanation for this effect is that hippocampal activity in rodents can interfere with other memory systems during the acquisition of procedural tasks with very low spatial requirements, as used here. Alternative explanations for the observed superior SRTT performance in lesioned animals, such as hyperactivity or increased exploratory drive are also topic of the discussion. © 2011 Wiley Periodicals, Inc.
ISSN:1050-9631
1098-1063
DOI:10.1002/hipo.20965