Effects of ectopias and their cortical location on several measures of learning in BXSB mice.

About half of BXSB/MpJ- Yaa mice have ectopias, which are misplaced clusters of neurons located in layer I of cortex. This study replicated several previous findings showing that there are learning differences between mice with ectopias and those without. In addition, we had sufficient numbers of ectopic mice to investigate if ectopics learned differently depending on the cortical location of the ectopia(s). Mice with at least one ectopia located in prefrontal cortex were initially impaired in learning the Morris maze, as well as relearning the Lashley maze when it was inverted, but learned better in the radial-arm maze when compared to ectopic mice with ectopias located in nonprefrontal regions of cortex. Mice with at least one ectopia in motor cortex learned the Lashley maze better than mice with ectopias located outside motor cortex. In sum, the cortical location of the ectopia(s) affected learning performance in certain tasks within the ectopic group, but regardless of the cortical location of the ectopia(s), ectopics still learned differently than nonectopics in several tasks. © 2001 John Wiley & Sons, Inc. Dev Psychobiol 39: 286–300, 2001