[History of the basal ganglia system. Slow development of a major cerebral system]

Initially, basal ganglia was a descriptive term for onto- and phylogenetic or topographic classifications. A variable list of structures were included as basal ganglia. A major step was made when the thalamus was separated from the "striated bodies" (Vic d'Azyr, 1786) which was sometimes taken into account in the French description of the noyaux gris centraux. Even if the term is not perfect, it is preferable to "the system of basal ganglia". The subdivisions of the putamen, the distinction between the striatum and the pallidum were not really made until the beginning of the twentieth century. Modern tracing methods were needed to demonstrate the main connections. It was not until the end of the 1960s that the importance of the striato-pallido-nigral network within the basal ganglia and the cortico-striatal connections, the main afferent system, were recognized. With the description of the cortico-striatal connections, the sub-cortical system with multiple complex "loops" was questioned. The term "extra-pyramidal system" had an exaggerated success. Initially, it designated descending non-pyramidal afferents (some which do not exist) and their source. In 1992, Spatz based his separation of this heterogeneous group on the iron content. The terms of extra-pyramidal "system" and "syndrome" should be abandoned by clinicians. Physiological interpretations have varied. The role of automatic "habitual" motricity, derived from a concept of hierarchic, Jacksonian cerebral organization, was questioned when the pyramidal network was described. Clinico-pathological analysis (hemiballism, Parkinson's disease ...) has placed new emphasis on the motor role, for a time the only role accepted as real. More recently, debate has centred on other roles, particularly in cognition and motivation. An illustration of functions other than purely motor functions of the basal ganglia is given by the syndromes of loss of psychic auto-activation secondary to bilateral lesions.