Ontogeny of T-maze behavioral lateralization in rats.

Behavioral lateralization has been reported in both humans and animals. In humans, lateralization can be detected in neonates and increases to adult levels during postnatal development. Recently we reported lateralization of head and tail movements in neonatal rats. However, the postnatal ontogeny of lateralization in animals has not been previously studied. This work presents a study of rat behavioral lateralization in the T-maze test during postnatal development (from day 30 to day 60). A decrease was found in absolute (percent preferred-side choices) and population (right-left arm choices) laterality between day 30 and day 45 of postnatal life. The lateralization degree remained unchanged between days 45 and 60. Because behavioral alternation increases from day 30 to day 45, the present data suggest that animal lateralization of behavior is a phenomenon that remains throughout the subject's life span, but whose behavioral quantification could be concealed by the ontogenic increases of other phenomena such us behavioral alternation. This hypothesis could explain the high level of lateralization in neonatal rats, the low level of rat lateralization during adulthood, and the increases in lateralization induced by stress.