P. M. S. Hacker - Philosophical Foundations of Neuroscience

The history of neuroscience shows that our understanding of cortical function is founded of necessity on correlations with human behaviour and experience. We now consider a different approach, based on logico-grammatical grounds, to the question of whether psychological attributes (seeing, thinking, remembering, etc.) can be attributed to a part of the cortex, either an anatomical part or a group of neurons.

This approach was initiated by Aristotle in the fourth century bc. Aristotle states in his De Anima that ‘To say that the psuche¯ is angry is as if one were to say that the psuche¯ weaves or builds. For it is surely better not to say that the psuche¯ pities, learns, or thinks, but that the man does these things with his psuche¯ .’ Here Aristotle is emphasizing that pitying, learning and thinking can be sensibly attributed only to human beings, not to some principle of life that informs their body, namely the psuche¯ (sometimes incorrectly translated as ‘soul’). In the nineteenth century Lewes restated Aristotle’ s conception in its modern form. In his The Physical Basis of Mind (1891) he states that ‘It is the man and not the brain, that thinks; it is the organism as a whole and not one organ that feels and acts.’ In the twentieth century Wittgenstein offers the same thought in his Philosophical Investigations (1953), ‘Only of a living human being and what resembles (behaves like) a living human being can one say: it has sensations, it sees; is blind; hears; is deaf; is conscious or unconscious.’

Aristotle, Lewes and Wittgenstein are pointing out that there are no logico-linguistic grounds for attributing psychological predicates to the brain, parts of the brain, or indeed any other parts of the body, rather than to behaving human beings. The logic of part/whole relations is known as mereology. The misattribution of psychological predicates by many neuroscientists we call the mereological fallacy in neuroscience. The conceptual confusions arising from this fallacy, together with the fact that the history of cognitive neuroscience is a search for correlations with behaviour, makes clear that it is humans that experience, not their brains or parts of their brains.

1 1M. R. Bennett, S. Hatton, D. F. Hermens and J. Lagopoulos, ‘Behavior, neuropsychology and f MRI’, Progress in Neurobiology, 145–146 ( 2016), pp. 3–6.

2 2Ibid., p. 17.

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

Aristotle’ s conception of the psuchē

Aristotle (385–322 bc) is the first great biologist many of whose treatises and observational data survive. His philosophical world picture shaped European thought until and, in certain respects, beyond the scientific revolution of the seventeenth century. So although his knowledge of the nervous system was almost non-existent, his fundamental conceptions of animate life are indispensable to an understanding of the reasoning of the early scientists, such as Galen and Nemesius, who probed the nature of the nervous system and its role in determining the cognitive, cogitative, affective and volitional powers of man. Moreover, as we shall see, Aristotle’ s conception of the nature of man, of the relation between organs and functions, between the body and the distinctive capacities that constitute what he called ‘the psuchē ’ was profound. The Aristotelian conception of the psuchē and the Cartesian conception of the mind, which displaced it in the seventeenth century, constitute in certain respects two fundamentally different ways of thinking about human nature, which have informed neuroscientific reflection on the integrative action of the nervous system throughout the ages.

The psuchē as the form of the natural body

Aristotle ascribed to each living organism a psuchē . The psuchē was conceived to be the form of a natural body that has life . 2It was also characterized as the first actuality of a natural body that has organs ( DA 412 b5–6). Aristotle’ s technical terminology needs elucidation.