The lateralization of the grasp reflex in human newborns.

The strength of the grasp reflex from the right and left hands was estimated in male and female newborns within the second day after birth. In the total sample (N = 121), the mean strength of the grasp reflex from the right hand was found to be significantly higher than that from the left hand. There was a significant positive linear correlation between reflex strengths from the right and left hands. The mean right minus left (R - L) reflex strength was found to be significantly larger than zero. There was a positive linear relationship between the R-L reflex strength and the reflex strengths from the right and left hands. This was more pronounced for the right hand than the left hand. The reflex strengths from the right and left hands were found to be positively linearly correlated with the weight of the newborn babies. These results indicated a grasp reflex lateralization in newborns. The right-bias in the grasp-reflex asymmetry established in this work would create a basis for the development of the right-hand preference in adulthood.