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 lat
eralization of head and tail movements in neonatal rats. However, the
postnatal ontogeny of lateralization in animals has not been previousl
y studied. This work presents a study of rat behavioral lateralization
in the T-maze test during postnatal development (from day 30 to day 6
0). 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 lif
e 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 neo
natal rats, the low level of rat lateralization during adulthood, and
the increases in lateralization induced by stress.