[Magnocellular and parvocellular red nuclei. Anatomico-functional aspects and relations with the cerebellum and other...

The term "red nucleus" (RN) applies to two different, independent nervous structures: the magnocellular RN (RNm) and parvocellular RN (RNp). During the phylogenesis of vertebrates, the RNm emerged in the first tetrapods, when animals became terrestrial. Its volume increased in mammals with the development of the intermediate cerebellum and the interposed nuclei, from which it receives afferents. Besides afferent fibres from the motor cortex, the RNm receives a direct projection from the spinal cord. This afferent pathway induces somaesthetic responses and corollary discharges of spinal activities. In view of its central and exteroceptive connections, it seems likely than the RNm might participate in the rapid updating of motor commands about the use of locomotor limbs. In primates, especially in man, the RNp is highly developed. This change took place simultaneously with the considerable development of the cerebral hemispheres and the dentate nucleus, which projects to the RNp. Considerable development of the cortical, parietal and frontal cerebral areas and of the principal olive of the medulla oblongata also occurred. All these structures are linked to the RNp by central connective loops, in a common network. In addition, motor activity in primates depends less on sensory cues and has become more intentional. Certain neurons in this nervous network have a very early activation, occurring well before the triggering of movement. This activity depends on the intention to move a limb more than on the movement itself. The hypothesis put forward here is that the RNp might participate in the elaboration of conscious voluntary movements, such as finger movements and speech.