Behavioral consequences of neonatal injury of the neocortex.

Several strains of autoimmune mice spontaneously develop molecular layer ectopias that are similar in appearance to those seen in humans and are caused by disturbances in neocortical neuronal migration. These mice also exhibit behavioral anomalies, some of which correlate with ectopias, others with the immunological disorder. In this study, we induced neocortical ectopias (via puncture wounds) and microgyria (via freezing lesions) in the neocortex of 1-day-old (newborn) mice without immune disorders in an attempt to further disentangle the effects of autoimmunity and of cortical malformation on behavior. In addition, we wished to compare the behavioral effects of small ectopias to larger microgyric lesions. DBA mice were assigned at birth to receive either a puncture wound or freezing lesion of either the left or right hemisphere. An independent group was subjected to sham surgery. In adulthood, these mice were given a battery of tests designed to measure lateralization and learning capacity. Lesioned mice (irrespective of hemisphere or type of damage) performed poorly when compared to sham-operated animals in discrimination learning, in a spatial Morris Maze Match-to-Sample task, and in a Lashley Type III maze. In shuttlebox avoidance conditioning, where immunological disorder has been shown to compromise behavioral performance in autoimmune mice, there was no difference between lesioned and sham animals. These results (1) support the dissociation between the effects of developmental neocortical anomalies and autoimmune disease on behavior (2) reveal similarities between spontaneous and induced neocortical malformations and (3) fail to support a difference in behavioral effects between ectopias and microgyria.