Evidence for anatomical but not functional asymmetry in the hemidecorticate rat

Rats with unilateral ablation of the left or right cerebral neocortex or left or right hippocampus were studied in a battery of tests of spatial orientation, motor coordination, and social behavior, including Morris water task, radial arm maze, feeding, narrow beam traversing, puzzle latches, hoarding, grooming, nest building, running wheel activity, male--male interaction, and shock-induced aggression. Comparison of the brains of operated and control rats confirmed previous suggestions that the right hemisphere of the rat is bigger and may have different connections than the left hemisphere. Despite the morphological asymmetries, comparison of the behavior of rats with right hemidecortication with that of rats with left hemidecortication, and of rats with right and of those with left hippocampal lesions, failed to show a single instance of functional asymmetry in the rat brain. These behavioral results stand in marked contrast to previous reports of functional asymmetry in the control of activity, orientation, and rotation.