The effects of early environment on the development of functional laterality in Morris maze performance.

The current study examined the contribution of early postnatal experience to the functional lateralisation of spatial ability in the male rat. Litters were handled (H) or non-handled (NH) during the first 20 days of life, and three males from each litter were tested in the Morris water maze in adulthood. Two subjects from each litter were monocularly tested, one with the right eye patched and the other with the left eye patched. A third subject in each litter was tested with both eyes open. Handling interacted with Eye Patch for time and distance measures. Performance of Right- and Left-Patched rats was equivalent for the NH group, but the H subjects tested with the Right Patch outperformed H subjects with the Left Patch. These results confirm studies that found spatial navigation performance to be lateralised to the right hemisphere in male rats. The data indicate that functional asymmetry of spatial navigation behaviour in the adult male rat is sensitive to environmental influences during early development.