Grasp-reflex strength from right and left hands in relation to serum cortisol level and fetal position in human neonates.

The grasp-reflex strengths from right (R) and left (L) hands were studied in human neonates in relation to serum cortisol levels and fetal position. In males with right-ear out, there was no correlation between grasp-reflex strength from right hand and cortisol. The grasp-reflex strength from left hand significantly decreased as cortisol increased linearly in these subjects. In males with left-ear out, the grasp-reflex strengths from right and left hands were found to be negatively linearly correlated with serum cortisol level. In females with right-ear out, the grasp-reflex strength from right hand was not significantly correlated with cortisol, but grasp reflex from left hand linearly decreased as cortisol increased. In females with left-ear out, only the grasp reflex from right hand linearly increased with cortisol. Only in males with right-ear out, the R-L grasp-reflex strength linearly increased from left dominance toward right dominance. It was concluded that the stress hormone cortisol may be disadvantageous and/or advantageous for the prenatal development of the right and left brain according to fetal position; cortisol may also affect the emergence of cerebral lateralization.