Relation of serum free-testosterone level to grasp-reflex strength in human neonates with right-ear and left-ear facing out in-utero positions.

The relation of the grasp-reflex strength to serum free-testosterone level was studied in human neonates with right and left ear facing out in utero positions. The grasp-reflex strengths from the right and left hands were found to be inversely correlated with testosterone in neonates with right-ear-out position. In neonates with left-ear-out in utero position, the grasp-reflex strength only from the left hand inversely correlated with testosterone. Left-dominance decreased and right dominance in grasp reflex increased linearly with testosterone only in females with left-ear-out in utero position. These results supported the theory of prenatal origins of cerebral lateralization (Previc, 1991). It was concluded that testosterone may favour the maturation of both hemispheres in neonates with right-ear-out in utero position, and only the right-hemispheric development in subjects with left-ear-out in utero position; testosterone may be a male hormone influencing the cerebral lateralization on the ground of genetically and even environmentally predetermined cerebral organization.