Читать книгу Philosophical Foundations of Neuroscience - P. M. S. Hacker - Страница 19

The conceptual framework for early investigations into the biological basis for human sensory, volitional and intellectual capacities was set by Aristotle’ s philosophical writings on the psuchē and pneuma. The early growth of neuroscientific knowledge was dominated by the question of how the contraction of muscles involved in voluntary movements of limbs is effected. However, Aristotle’ s own rudimentary investigations, which led him to believe that the blood vessels initiate muscle contraction, were a false start. It was, above all, Galen’ s much later discoveries of the nerve supply to muscles from the spinal cord that made it clear that it is the nerves that carry out this function. Galen’ s work initiated 2,000 years of enquiry into how the spinal cord and brain are involved in voluntary movement and into the reflex origins of some movements. The identification of motor and sensory spinal nerves, the role of the spinal cord in reflex movements, and the relationship between the action of the brain and the spinal cord in voluntary and reflex movement were all resolved by experiments. These involved observations on muscles and limbs following lesions to different parts of the nervous system. In this way a conception evolved of how the functions of the brain, spinal cord and nerves are integrated to give the final motor output.

The conceptual framework within which neuroscientific knowledge grew originated in Aristotelian thought, but it was subsequently transformed by the Cartesian revolution in the seventeenth century. In this chapter we shall adumbrate the development of ideas concerning the neural basis of animate functions, concentrating increasingly upon what Sherrington, among the greatest of neuroscientists, called ‘the integrative action of the nervous system’, as it applies to movement. This sketch of the history of the slow growth of knowledge about the nervous system and its operations will display some of the conceptual difficulties encountered by natural philosophers over the centuries as they grappled with the problems concerning the biological foundations of characteristic powers of animate beings in general, and humans in particular. As we shall see, the roots of current conceptual difficulties in cognitive neuroscience are buried deep in the past. Grasping this aspect of our intellectual and scientific heritage will help to bring current conceptual problems into sharp focus. These problems are the principal concern of this book.

It might be asked why we do not concentrate more on the role of the great sensory systems, such as vision, in our historical sketch of the integrative action of the nervous system. The reason is that the early neuroscientists took up the challenge of understanding the motor system first, for it allowed experimentation which they could undertake to test their ideas with the techniques then available. This was not the case with the sensory systems. These pioneers saw the need to integrate their account of the sensory systems into their evolving knowledge of muscular contraction and movement. This led them to speculate on the relationship between vision and motor performance. It did not, however, add much to our understanding of how vision occurs, a subject that had to wait for techniques that became available only in the nineteenth and especially the twentieth century.¹