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The lateralization of the grasp reflex in human newborns
1Atatürk University, Medical Faculty, Department of Physiology, Erzurum, Turkey.
Insights
Newborns show a stronger grasp reflex in their right hand compared to their left. This early asymmetry in grasp reflex may lay the foundation for adult right-hand preference.
Area of Science:
- Neuroscience
- Developmental Psychology
- Human Motor Development
Background:
- Hand preference is a common trait in adults.
- The developmental origins of hand preference are not fully understood.
- Early infant reflexes may provide insights into later motor asymmetries.
Purpose of the Study:
- To investigate the strength of the grasp reflex in newborn infants.
- To determine if there is an asymmetry in grasp reflex strength between the right and left hands.
- To explore the relationship between grasp reflex strength and infant weight.
Main Methods:
- Assessed grasp reflex strength in 121 male and female newborns on their second day of life.
- Compared reflex strength between the right and left hands.
- Analyzed correlations between right and left hand reflex strengths, reflex asymmetry, and infant body weight.
Main Results:
- The mean strength of the grasp reflex was significantly higher in the right hand than the left hand.
- A significant positive linear correlation was observed between right and left hand reflex strengths.
- Right-hand dominance in grasp reflex asymmetry was positively correlated with overall reflex strength and infant weight.
Conclusions:
- Newborns exhibit grasp reflex lateralization, with a right-hand bias.
- This early-established asymmetry in grasp reflex may be a precursor to the development of right-hand preference in adulthood.
Abstract:
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.