General movements in early infancy: what do they tell us about the nervous system?

Developmental changes in muscle coordination patterns of normal and abnormal general movements (GMs) are described. GMs were studied simultaneously with video-recording and polymyography (polyEMG). GMs of normal full-term infants gradually lose their neonatally slow and 'writhing' character, to be turned into the elegant flow of small movements of 'fidgety' GMs at the age of 2-3 months. This transformation coincides with changes in the polyEMG. Tonic background activity decreases concurrent with a reduction in amplitude and duration of phasic bursts. The coordination between antagonistic muscles does not change, co-activation remains the prevailing pattern. Secondly, preliminary results on healthy preterms (n = 6) are presented. At the examination age of 33-34 weeks postmenstrual age the preterms showed so-called 'preterm' GMs, which are characterized by variation and graceful complexity. EMG burst duration was significantly longer during 'preterm' GMs than during 'writhing' GMs of full-term newborns. The percentage of co-activation during 'preterm' GMs varied considerably. The polyEMG of 'writhing' GMs of two preterms, who were followed longitudinally, differed from that of 'writhing' GMs of full-terms. At 'fidgety' age the EMG differences between preterms and full-terms had disappeared. Finally the first results on abnormal GMs are reported. A synchronized onset of muscle activity in all extremity muscles and 'packaging' of EMG-bursts into subunits of 5-8 Hz. seemed to be specific properties of these abnormal GMs. This could indicate a loss of supraspinal control.