Normal learning ability of mice with a surgically exposed hippocampus.

In rats and mice, the hippocampus lies beneath higher than 1 mm of the neocortex. This anatomical feature makes it difficult to experimentally access the hippocampus from the surface of the brain in vivo. This problem may be solved by surgical removal of the cortical tissue above the hippocampus; however, it has not been examined whether this 'hippocampal window' surgery preserves the normal hippocampal function. We bilaterally aspirated the posterior parietal cortex above the dorsal hippocampus of adult male mice. These mice still exhibited normal local field potentials of the hippocampus, normal motor activity, and normal cognitive ability in the water-maze test and contextual fear conditioning, compared with intact or sham-operated controls. Thus, exposed hippocampal preparations provide a useful experimental model to study the physiology of the hippocampus.