NEOCORTICAL ECTOPIAS IN BXSB MICE - EFFECTS UPON REFERENCE AND WORKING-MEMORY SYSTEMS

BXSB mice have an similar to 40-60% incidence of neocortical ectopias in layer I of the prefrontal/motor cortex. Prior studies have found ma jor behavioral differences between those with ectopias and their non-e ctopic littermates. Some of these findings indicate that the two group s differ with respect to spatial reference and working memory. The pur pose of this study was to measure reference and working memory in the same animals to test the hypothesis that the ectopics would have bette r reference memory but less effective working memory. The Lashley III maze has cul-de-sacs which must be eliminated, and T-choices where the animal has to decide whether to go left or right. Ectopic and non-ect opic mice were equally able to learn the maze and did not differ on cu l-entry or T-choice errors. Then the maze was inverted and the animals were retested. Turning the maze upside down did not change the relati ve status of the blind alleys. Therefore, the reference memory knowled ge from the prior week's training could be used to avoid entering the culs. However, inverting the maze caused a left-right mirror image rev ersal of the T-choices. Therefore, prior reference memory information would interfere with learning the new path through the maze, whereas w orking memory would enable the mouse to eliminate T-choice errors. Ect opic mice made less cul-entry errors and more T-choice errors than the ir non-ectopic littermates, as predicted.