A CRITICAL-EXAMINATION OF THE MORO RESPONSE IN NEWBORN-INFANTS - SYMMETRY, STATE RELATION, UNDERLYING MECHANISMS

The primary purpose of the present study was to analyze quantitatively the vestibular evoked Moro response, and the symmetry of the movement pattern involved, as the traditional descriptions bring about. Anothe r aim was to determine the segmental movements involved and determine whether the components of the Moro response are dependent on changes i n the infant's behavioral state. Another question concerns whether the form of these movements changed over repeated trials on the same day, or from the first to the fifth day after birth. Vestibular evoked Mor o responses of 52 neonates, 1-5 days of age, elicited in different beh avior states (State 1-5), were examined and quantitatively analyzed, T he response was evoked by a predefined, rapid, downward, vertical body motion, without any dorsiflexion of the infant's head. Optoelectronic device (SELSPOT II) were used to monitor the arm/hand movement patter ns involved in the response. The three-dimensional movement pattern in space, duration, velocity, latency, and the acceleration of both arms /hands were analyzed in relation to the infant's behavioral state. The response movements were structured into phases of abduction/extension , adduction/flexion and the extension/flexion of the fingers, The vest ibular stimulation used was found to be sufficient for eliciting an ad equate Moro response. The segmental movement pattern of the Moro respo nse was found to be sensitive to the infant's behavioral stale at the time when the response was elicited. This was found in the movement pa ttern, duration, latency, and the velocity of the response. The respon se was found to be asymmetrical, in 82% of the infants it was found to be a predominant shorter onset latency of the right arm, in 12% the o pposite was found. These findings suggest that there is a fundamental, spinal asymmetry involved in the Moro response which is subject to su praspinal influences emanating from the vestibulospinal system. No dif ferences were found between 1 and 5 days of age for any of the scoring categories, and no differences were found within groups over six succ essive trials.