抄録
In the present study, a novel procedure of non-matching-to-place (NMTP) task in the radial maze was devised and the effects of lesions of the entorhinal cortex and hippocampus on spatially guided working/reference memory were investigated. Both groups of rats with the entorhinal and hippocampal lesions showed severe impairment of performance on the NMTP task at delay of 0 min, whereas sham lesioned rats rapidly reacquired the task. Overtraining of the NMTP task before lesion considerably ameliorated behavioral performance of rats with the entorhinal cortex lesion, although hippocampal lesioned rats showed no improvement of performance. When various delay intervals (0, 1, 3, and 9 min) were randomly interposed between the information run and the choice run in the delayed NMTP test, delay-dependent impairments were shown in the entorhinal lesioned rats which reacquired postoperative NMTP task. These results indicate the possibility of differential effects of overtraining on the entorhinal cortex and hippocampus, in that the entorhinal-hippocampal system is initially involved in both spatially guided working and reference memory, and after overtraining, reference memory as well as spatially guided working memory is left on the function of the hippocampus, but the entorhinal cortex becomes to play a critical role of spatially guided working memory.
