A detailed analysis of rats' spatial memory in a probe trial of a Morris task.

In the present study, we evaluated the search behavior of rats during a probe trial of a Morris water escape task. More specifically, the spatial memory during different stages of a 2 min probe trial in different zones was examined. After rats were trained for 4 days with four trials per day, their spatial memory was tested in a first probe trial. The rats showed a preference for the target quadrant during each of four 30-s intervals. The time in the annulus decreased across the four 30-s intervals. The preference for the previous target quadrant was also observed in a second probe trial, when the rats had received additional training for 4 days with four trials per day. However, the time spent in the annulus was highest during the first 30-s of the probe trial, and was lower and similar during the next three 30-s intervals. Therefore, probe trials of 60s seem to underestimate the spatial ability of rats. It appears that using a quadrant for assessing the performance may overestimate the spatial ability of a rat. Our findings suggest that the evaluation of the spatial memory of rats in a probe trial in the Morris water escape task requires a more detailed analysis.