The Neuronal Group Selection Theory : a framework to explain variation in normal motor development

During the last century, knowledge of the mechanisms governing the functions of the central nervous system increased rapidly as sophisticated physiological, neurochemical, and imaging techniques developed. In the field of motor control, better understanding of neurophysiology caused a gradual shift from the concept that motor behaviour is largely controlled by reflex mechanisms towards the notion that motility is the net result of complex spinal or brainstem activity, which is subtly modulated by segmental afferent information and ingeniously controlled by supraspinal networks. Nowadays it is assumed that motor control of rhythmical movements like locomotion, respiration, sucking, and mastication is based on so-called central pattern generators (CPGs): neuronal networks which can generate complex basic activation patterns of the muscles without any sensory signals. Nevertheless, sensory information of the movement is important in adapting the movement to the environment. The activity of the networks, which are usually located in the spinal cord or brainstem, is controlled from supraspinal areas via descending motor pathways. The supraspinal activity itself is organized in large-scale networks in which cortical areas are functionally connected through direct recursive interaction or through intermediary cortical or subcortical (striatal, cerebellar) structures.