CA1 ischemic injury does not affect the ability of Mongolian gerbils to solve response, direction, or place problems

Open field and T-maze paradigms are used to test the effects of hippocampal lesions on spatial memory in rodents. Place cells in the dorsal CA1 region of the hippocampus are known to be responsible for the formation of global place maps, while CA3 neurons respond to changes in local contexts. It is proposed here that when dorsal CA1 is selectively destroyed, gerbils will be unable to solve direction and place problems while context-dependent representations of relative maze positions should be spared since CA3 cells are left intact. Twenty female Mongolian gerbils were subjected to 5 min of forebrain ischemia, and, along with 20 controls, were subsequently tested on a response, direction or one of two types of open field place problems. Locomotion in a circular open field was recorded as a measure of hyperactivity. Gerbils with damage restricted to dorsal CA1 were hyperactive compared to controls, but were not impaired on place, direction, or response tasks. Because gerbils solved these tasks in the absence of dorsal CA1, maze tasks which have traditionally been labeled "place" or "direction" tasks may actually be testing the animal's ability to discriminate between two relative contexts, without the need for a global place map. Our findings support recent reports that different hippocampal subfields control different aspects of spatial learning and memory. Specifically, the context-dependent representations in CA3 appear to support the learning of the "place" and, likely, "direction" solutions in current and previous open field and T-maze tasks.