as operating upon the pineal gland to generate the minute fluctuations in the animal spirits (the role-equivalent of neural transmitters) in the ventricle in which he thought the pineal gland was suspended. This, he held, enabled the acts of will of the mind to affect the motions of the animal spirits, which are then transmitted to the muscles. But the question of how an immaterial substance could actually interact causally with a material object such as the pineal gland to produce the appropriate minute motions was left totally unanswered. In much the same way, Eccles thought that the ‘self-conscious mind’ interacts causally with the pyramidal cells of the motor cortex, gradually (rather than instantaneously) getting them to discharge. But the question of how an immaterial entity such as the mind can interact causally with neurons was left equally unanswered.
(2) Reifying the mind
Both thinkers erred in conceiving of the mind as an entity of some kind. Had they heeded Aristotle in thinking of the mind, or more accurately, of the psuche-, not as an entity but as an array of powers or potentialities, they would have been much closer to the truth, and would not have become enmeshed in insoluble problems of interaction. For it patently makes no sense to ask how one’s abilities to do the various things one can do interact with one’s brain.
(3) Misconceptions about the will
Both thinkers erred in imagining that voluntary movements are movements produced or caused by antecedent acts of will.15 For although there are such things as acts of will – namely, acts performed with great effort to overcome one’s reluctance, aversion or difficulties in acting in adverse circumstances – obviously the vast majority of our ordinary voluntary actions involve no ‘act of will’ in this sense at all. We shall examine this conception in chapter 9.
Eccles was further confused over the object of the alleged act of will, which is variously characterized as (i) a muscular movement, (ii) an action or (iii) a movement of a limb.
Confusions about the object of the alleged act of will
It is, of course, possible to intend to move a muscle – for example, to flex a muscle – but that is something we rather rarely intend to do, and although the movement of muscles is involved in all our positive, physical acts ( by contrast with acts of omission and mental acts), what we intend, and what we voluntarily perform, are actions (such as raising our arm, writing a letter, saying something, picking up a book, reading a book, and so on), and not the constitutive muscle movements of these actions, of which we are largely unaware. But it is easy to see why a neuroscientist who is attracted to dualism should confuse the objects of the will. For, according to the dualist conception, the mind has causally to affect the brain, and the causal powers of neural events in the brain causally affect muscle contraction.
Problems of volitional interaction between mind and brain
This raises yet a further insoluble problem for the dualist. The ‘self-conscious mind’ is supposed to influence the pattern of module operation, gradually moulding and directing it so that it concentrates on the pyramidal cells in the proper zones of the motor cortex for carrying out the intended movement. But how does the ‘self-conscious mind’ know which pyramidal cells to concentrate on, and how does it select the proper zones of the motor cortex? For it would need such knowledge in order to execute such actions. And it is certainly not knowledge of which the self-conscious mind is conscious. To these questions there can be no answers, any more than the nineteenth-century innervationist ideo-motor theories of voluntary movement (chapter 9), favoured by such eminent scientists as Helmholtz and Mach (and psychologists such as Bain and Wundt), could answer the question of how the mind, in addition to having images of kinaesthetic sensations that allegedly accompany voluntary movements, directs the currents of energy going from the brain to the appropriate muscles. ( There must be appropriate feelings of innervation – of ‘impulse’ or ‘volitional energy’, they thought, otherwise the mind could never tell which particular current of energy, whether the current to this muscle or the current to that one, was the right one to use.)
Eccles’s conception of the implications of Sperry’s discoveries about results of split-brain operations
A second piece of empirical research encouraged Eccles in his advocacy of interactionist dualism. Sperry’s discoveries concerning the capacities of split-brain patients were striking. He himself took them to vindicate some form of mind–brain interactionism:
Conscious phenomena in this scheme are conceived to interact with and to largely govern the physiochemical and physiological aspects of the brain process. It obviously works the other way round as well, and thus a mutual interaction is conceived between the physiological and the mental properties. Even so, the present interpretation would tend to restore the mind to its old prestigious position over matter, in the sense that the mental phenomena are seen to transcend the phenomena of physiology and biochemistry.16
It is therefore unsurprising that Eccles thought that Sperry’s work had dramatic implications. ‘It is my thesis’, he wrote, ‘that the philosophical problem of brain and mind has been transformed by these investigations of the functions of the separate dominant and minor hemispheres in the split-brain subjects’ (HM 222). The ‘most remarkable discovery’, Eccles held, was that all the neural activities in the right hemisphere ‘are unknown to the speaking subject, who is only in liaison with the neuronal activities in the left [dominant] hemisphere’. To be sure, the right hemisphere is ‘a very highly developed brain’, but it ‘cannot express itself in language, so is not able to disclose any experience of consciousness that we can recognize’. The dominance of the left hemisphere, he argued, is due to its verbal and ideational abilities, and ‘its liaison to self-consciousness ( World 2)’ (HM 220). For what Sperry’s work shows, Eccles averred, is ‘that only a specialized zone of the cerebral hemispheres is in liaison with the self-conscious mind. The term liaison brain denotes all those areas of the cerebral cortex that potentially are capable of being in direct liaison with the self-conscious mind.’17
Eccles’s conception of the liaison brain and Descartes’s conception of the pineal gland compared
Descartes thought that the pineal gland was the point of contact of the mind and the brain, and that the mind apprehends what is before the eyes of the body in virtue of the images that come from the two eyes and are united on the pineal gland. Eccles thought that the liaison brain was the point of contact with the mind, where the nerve impulses from the sense-organs are, in some sense, made available to the mind. But there is an interesting difference between the two doctrines. Descartes thought that the pineal gland itself – that is, a part of the brain – fulfils the task of the Aristotelian and scholastic sensus communis, the task of synthesizing and unifying the data of the separate senses. In this respect, his thought was more up to date than Eccles’s, since contemporary neuroscientists think likewise that the ‘binding problem’ is solved by the brain (rather than by the mind).18 For Singer’s discoveries19 of coherent oscillatory firings in disparate parts of the brain concomitant with perceptual experience suggest that the simultaneity of these manifold neuronal activities and their connections to other areas of the cortex are necessary conditions for a perceiver to have the kind of unified perceptual experience we have. Eccles, by contrast, defended what he called ‘the strong dualist hypothesis’ that
the self-conscious mind is actively engaged in reading out from the multitude of active modules at the highest levels of the brain, namely in the liaison areas that are largely in the dominant cerebral hemisphere. The self-conscious mind selects from these modules according to attention, and from moment to moment integrates its selection to give unity even to the most transient experience. Furthermore, the self-conscious mind acts upon these modules, modifying the dynamic spatio-temporal patterns of the
