The developmental origins of laterality: fetal handedness.

This paper reviews the evidence for lateralized motor behavior in the fetus around a number of key questions: does the fetus exhibit signs of laterality? when does lateralized motor behavior begin? is the lateralized preference consistently displayed? does prenatal handedness relate to postnatal handedness? and, does prenatal handedness relate to brain functioning? The evidence indicates that the fetus exhibits lateralized behavior from 10 weeks gestation, as soon as it independently moves its arms, and this is the precursor of lateralized motor behavior observed post-natally. Data is presented suggesting that the strength of laterality decreases with advancing gestation and this correlates with more efficient information processing as assessed by habituation. However extreme caution is warranted in attempting to link asymmetric motor behavior and brain function prenatally. The paper concludes that the initial developmental emergence of lateralized behavior is under genetic control and is a fundamental feature of prenatal human development.