Sensorimotor and Motivational Determinants of Hand-Mouth Coordination in 1-3-Day-Old Human Infants

Hand-mouth coordination was studied in l-3-day-old human infants by delivering 0.2 ml of sterile 12% sucrose solution intraorally once every 2 min. Sucrose was extraordinarily calming and caused sustained hand-in-mouth contact. The calm state persisted well beyond sucrose termination. Handin-mouth behavior, however, stopped upon sucrose termination, demonstrating stimulus control over this integrated behavior. In subsequent studies we demonstrated that hand-in-mouth behavior was not attributable to calming per se. Moreover, hand activity could be prevented by placing a pacifier in the mouth. This demonstrates that the behavior was under intraoral somesthetic control and was not necessarily the expression of a motor pattern triggered by the sweet taste. These findings are interpreted within the contexts of sucrose (a) calming through an endogenous opioid system and (b) activating suckling-feeding mechanisms, causing the expression of integrated hand, mouth, and head motor patterns.