Effects of Unilateral Entorhinal Cortex Lesion on Retention of Water Maze Performance

In a previous study, adult male Sprague-Dawley rats with unilateral, electrolytic entorhinal cortex lesions showed significant deficits in acquisition of a water maze task that measured working memory. The 10 days of testing used two trials per day with an intertrial interval of 1 h, and the rats with entorhinal damage were impaired in total distance to the platform in both trials. In the present retention study, rats who learned the same task prior to injury and were then retested for 5 days after lesion showed only a first day deficit in total distance to platform in the second trial. Analysis of swim patterns indicated that rats with unilateral entorhinal lesions used an altered strategy in retention testing to find the platform in the second trial of each day and incorporated the use of headings appropriate for Trial 1 only. This altered or compensatory strategy was not the optimum choice for problem solution. Although the rats then were able to switch headings and find the platform without significant impairment in total distance to platform on days 2–5 of testing, the use of an initial incorrect strategy indicated subtle residual deficits in cue integration and use of working memory.