Neonates show an asymmetric degree of head rotation but lack an asymmetric tonic neck reflex asymmetry: Neuropsychological implications

Abstract

The spontaneous orientation preferences of 75 neonates were examined in terms of the direction and extent of head turning. Children who preferred to turn right ward rotated their heads more extremely to the right than to the left, whereas children who preferred to turn leftward showed less of an asymmetry in the extent of head rotation. This was taken as evidence that the neural asymmetry underlying neonatal orientation preferences is primarily motor rather than sensory. Another finding was that the asymmetric tonic neck reflex (ATNR) was as easy to elicit in response to left as to right head turns, even when extent of head turning was controlled for. This symmetry of the ATNR in neonates contrasts with the asymmetry of this reflex observed in older infants by Liederman and Coryell (1981). Thus, during early infancy, the ATNR may disappear earlier from the limbs on the side toward which the infant prefers to turn. The early disappearance of this reflex may free the limbs for volitional movement, thereby p...