Lateralization of the grasp reflex in male and female human newborns

The lateralization of the grasp reflex was studied in male and female newborns. The mean grasp-reflex strength of the right hand was found to be higher than that of the left hand in males, but the difference was not significant. The mean grasp-reflex strength of the right hand was found to be significantly higher than that of the left hand in females. There was no significant difference between the mean grasp-reflex strengths of the right hand in the male and female subjects. The mean reflex strength of the left hand was found to be higher in males than females; the difference was only marginally significant. The right minus left (R - L) reflex strength showed a significant positive linear relation to the right-and left-reflex strengths in both sexes. This was, however, much more pronounced for the right-reflex than the left-reflex. There was a significantly positive linear correlation between the reflex strengths of the right and left hands and the body weight in males. The females did not show such a relationship between reflex strength and body weight. These sex-related differences in the grasp reflex in newborns were discussed in light of cerebral lateralization and its hormonal modulation.