Lateral biases in head turning and the Moro response in the human newborn: are they both vestibular in origin?
Head turning after release from the midline and the Moro response to a full-body drop in 15 full-term newborns lying supine on a custom-built platform was studied. While the lateral bias for head turning was not as pronounced as for the Moro response, it was still assumed in the ratio of 2 (right):1 (left) as predicted by Previc (1991). Onset latency and time-to-peak acceleration were both significantly shorter in the right arm during the initial phase of the Moro response. For both measures, this right arm bias persisted over four consecutive elicitations in most infants. Vaginally delivered infants and those born by Caesarean section did not differ in terms of head preference and the two measures of arm advantage. Our main finding was that infants with a right-sided head preference had a consistently shorter onset latency for the right arm. We interpret this association as stemming from a common labyrinthine asymmetry that involves different vestibulospinal pathways for the neck and arm muscles. In general, our findings are discussed in the context of Previc's (1991) left-otolithic dominance hypothesis and Grattan, De Vos, Levy, and McClintock's (1992) model of newborn functional asymmetries.
Rönnqvist
L
L
Department of Psychology, Umeå University, Sweden.
Hopkins
B
B
van Emmerik
R
R
de Groot
L
L
D002585:Cesarean Section; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn / Q000502:physiology*; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012016:Reference Values; D012018:Reflex / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D014726:Vestibular Nuclei / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000502:physiology*