Читать книгу Philosophical Foundations of Neuroscience - P. M. S. Hacker - Страница 25

It is to Charles Sherrington (1857–1952) at the end of the nineteenth and the beginning of the twentieth century that one must turn to find an experimental plan for elucidating the mechanisms of the ‘true spinal marrow’. The thoroughness and methodical nature of Sherrington’ s researches on the subject are at a new level. These were not dependent on technical advances at the time so much as on the brilliance and clarity of his thinking, coupled with a formidable and indefatigable capacity for experiment. Sherrington first elucidated the spinal origin of the efferent nerves innervating a particular muscle.⁸⁵ In 1905 his experiments indicated that stimulation of the afferent nerves of a particular muscle could produce contraction of that muscle independent of contraction of opposing muscles of the joint.⁸⁶ In 1910 he published his great paper, nearly 100 pages long, on ‘Flexion-reflex of the limb, crossed extension-reflex, and reflex stepping and standing’.⁸⁷ In this he first describes the flexion-reflex and identifies the extension reflex as well as the crossed-extension reflex. This work, together with his earlier papers of 1897 and 1907, laid down the conceptual scheme for the analysis of the role of the spinal cord in stepping and standing. In doing this, Sherrington completed the research programme initiated eighty years earlier by Marshall Hall, with the consequence that the notion of a ‘spinal soul’ was finally eliminated from further consideration.

Although Ferrier in 1886 had first located the motor cortex in primates as a distinct area, it was Grunbaum and Sherrington in 1902 who first gave a detailed description of the spatial extent of this area on the cortex of primates.⁸⁸ They noted that the ‘motor’ area does not at any point extend behind the sulcus centralis. In this Sherrington and Grunbaum clearly distinguished for the first time the motor area from the area behind the sulcus centralis that we now know as somatosensory.⁸⁹ Their method of unipolar Faradization (alternating current) stimulation of the cortex allowed for much finer localization than had been possible with the double-point electrodes used up to this time.⁹⁰ Their classic paper, published at the beginning of the twentieth century, established without equivocation the conception of a motor cortex and therefore that different parts of the cortex are specialized for different functions.

The notion of a ‘spinal soul’ had been put to rest, largely through Sherrington’ s detailed elucidation of spinal reflexes. However, the relationship between the soul and the cortex, or between the mind and the brain, still bedevilled Sherrington, as it had neuroscientists and philosophers for more than two millennia. Sherrington engendered similar concern for it amongst his protégés. We shall explore this in the next chapter.