General movements during prenatal and early postnatal life

During the last century knowledge of the mechanisms governing the functions of the central nervous system (CNS) has rapidly increased. This expansion in knowledge was brought about by the development of sophisticated physiologic, neurochemical, and imaging techniques. In the field of motor control, the augmented understanding of neurophysiology resulted in a gradual shift from the concept that motor behavior is largely controlled by reflex mechanisms ¹ , ² towards the notion that motility is the net result of the activity of complex spinal or brainstem machineries, which are subtly modulated by segmental afferent information and ingeniously controlled by supraspinal networks. ³ For instance, nowadays it is assumed that motor control of rhythmic movements such as locomotion, respiration, sucking, and mastication is based on so-called central pattern generators (CPGs). CPGs are neural networks that are able to coordinate autonomously (i.e., without segmental sensory or supraspinal information) the activity of many muscles. Of course, in typical conditions, the CPG network does not work autonomously, but is affected by signals from other parts of the nervous system. The activity of the networks, which are usually located in the spinal cord or brainstem, is controlled from supraspinal areas via descending motor pathways. ³ The supraspinal activity itself is also organized in networks, large-scale ones, in which cortical areas are functionally connected through direct recursive interaction or through intermediary cortical or subcortical (striatal and cerebellar) structures. ⁴ , ⁵