LATERALIZED BEHAVIOR IN FIRST-TRIMESTER HUMAN FETUSES

Behavioural lateralisation is a common feature of everyday behaviour, most familiar in the exhibition of handedness. Despite differing theor ies about the origins of laterality, little is known about their ontog enesis. This study observed the left and right arm movements of 72 foe tuses at 10 weeks of gestational age, the first age at which lateralis ed behaviour may be observed. There was a highly significant preferenc e for foetuses to move their right arm more than their left arm, 85% e xhibiting more right arm than left arm movements. There was no differe nce in the amount of movements exhibited with the preferred arm, wheth er it be right or left. Laterality of behaviour at such an early gesta tional age (probably as early as it is possible for it to be observed) is unlikely to be under brain control but is probably of more muscula r or spinal determination. The possibility that early differential mot or behaviour may contribute to subsequent laterality of behaviour and asymmetrical brain growth, must be considered. (C) 1998 Elsevier Scien ce Ltd. All rights reserved.