The effects of neocortical ectopias on learning and memory in the BXSB mouse; and massed versus spaced learning in the NZB mouse

Date of Completion

January 1998


Biology, Neuroscience|Psychology, Psychobiology




The BXSB mouse has been used as an animal model for learning disabilities, including developmental dyslexia. The brains of dyslexics have neocortical ectopias, which are clusters of neurons abnormally located in layer I of cortex. Further, dyslexics demonstrate working memory deficits, but often excel in other areas. BXSB mice that have structurally similar ectopias also have working memory deficits, but are superior in other tasks when compared to BXSB mice without ectopias.^ Past studies demonstrated that ectopic BXSB mice had inferior spatial working memory, superior spatial reference memory, and equivalent non-spatial reference memory. Our studies showed that when working and reference memory were assessed together in a water version of the radial-arm maze, ectopic BXSB mice had inferior spatial working, equivalent or inferior spatial reference memory, superior non-spatial working memory, and equivalent non-spatial reference memory. When reference memory was assessed alone, ectopics had better spatial and non-spatial reference memory. The data suggest that the effects of ectopia on learning and memory depend upon the spatiality and cognitive demands of the tasks. Further examination of previous data and the data collected here suggested that ectopic BXSB mice also demonstrated impaired behavioral flexibility with spatial tasks.^ Previous studies reported that NZB mice were unable to learn the Lashley III water maze, while they could learn the Morris maze and discrimination learning. The Lashley maze had spaced trials, while the Morris maze and discrimination learning had massed trials, suggesting that NZB mice could only learn tasks with massed trials. NZB mice had hippocampal neuroanatomical abnormalities, including hippocampal ectopias and small intra- and infra-pyramidal mossy fibers, either of which could have been related to the learning limitations of NZB mice. Massed and spaced learning in several different learning tasks were examined in NZB and other mice. Unfortunately, the data suggested that trial spacing does not affect NZB learning and that further examinations of underlying neuroanatomical mechanisms were therefore unwarranted. ^