A BRIEF HISTORY OF THE BASAL GANGLIA

It was as early as 1664 when the first clear identification of distinct subcortical structures was published by the English anatomist Thomas Willis (Parent, 1986). What is now functionally known as the basal ganglia was then referred to as the corpus striatum. It held such a central position, striped with a wide range of cortical and brainstem fibers, that at the time it was believed to be the "sensorium commune" as defined by Aristotle. It was a structure thought to both receive all sensory modalities and initiate all motor acts. This idea appeared to be anatomically reinforced by its central position and clearly visible ascending and descending fiber systems.

Two subsequent events relegated the corpus striatum to an obscure and less defined position. The attractiveness of the histological organization of the cortex, and the possibility of localizing higher mental functions drew many neurologists of both the 18th and 19th centuries to cortical research. Amongst those that continued studying the corpus striatum, there was a sudden realization that many of the functions originally assigned to it were in fact properties of neighbouring corticospinal paths (Wilson, 1914). As Wilson (page 428) describes, the corpus striatum "seemed to fall from its high estate and depreciate in physiological significance".

At the beginning of the 20th century there were serious attempts to provide detailed comparative descriptions of the corpus striatum (Wilson 1914, Cajal 1911 - shown left). It began to gain importance once again with the discoveries that lesions of these areas would often result in disorders of motor functions in humans (Wilson 1914, Vogt 1911). The corpus striatum came to be viewed as the major components of the "extrapyramidal motor system" (Parent, 1986). This term loosely grouped the corpus striatum with an array of brain stem nuclei and reflected the assumption that this grouping constituted a complete and independent motor unit (Carpenter 1981). The term "basal ganglia" has been generally used to refer to these major anatomical telencephalic subcortical nuclei at the base of the forebrain. More formally this definition groups the corpus striatum (striatum and globus pallidus) with the substantia nigra and subthalamic nucleus.

written by Andrew Gilies