Philosophical Foundations of Neuroscience. P. M. S. Hacker
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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 neuronal events. Thus the self-conscious mind exercises a superior interpretative and controlling role upon the neuronal events both within the modules and between the modules. A key component of the hypothesis is that the unity of conscious experience is provided by the self-conscious mind and not by the neuronal machinery of the liaison areas of the cerebral cortex. Hitherto it has been impossible to develop any neurophysiological theory that explains how a diversity of brain events comes to be synthesized so that there is a unified conscious experience … My general hypothesis regards the neuronal machinery as a multiplex of radiating and receiving structures ( modules). The experienced unity comes, not from a neurophysiological synthesis, but from the proposed integrating character of the self-conscious mind. I conjecture that in the first place the raison d’être of the self-conscious mind is to give this unity of the self in all its conscious experiences and actions.(HM 227f.)
How does the mind engage in this activity of synthesis (or ‘binding’)? Eccles suggested that the mind
plays through the whole liaison brain in a selective and unifying manner. The analogy is provided by a searchlight. Perhaps a better analogy would be some multiple scanning and probing device that reads out from and selects from the immense and diverse patterns of activity in the cerebral cortex and integrates these selected components, so organizing them into the unity of conscious experience … Thus I conjecture that the self-conscious mind is scanning the modular activities in the liaison areas of the cerebral cortex … From moment to moment it is selecting modules according to its interests, the phenomena of attention, and is itself integrating from all this diversity to give the unified conscious experience.(HM 229)
Four flaws in Eccles’s conception
The metaphors are striking, and have echoes in current neuroscientific theory.20 Nevertheless, Sperry’s discoveries have none of the dramatic implications that Eccles imputed to them. There are four flaws in Eccles’s conception to which we wish to draw attention.
(1) The phenomena resultant upon hemispherectomy were misdescribed
First, the phenomena were misdescribed. It is not just the neural activities of the right hemisphere that are unknown to the subject – all the activities of the brain are unknown to subjects, who do not, after all, perceive their own brains (and, even if they could, do not have electron microscopes for eyes). It is true that the right hemisphere cannot ‘express itself in language’, any more than the right leg – because there is no such thing as a part of a human being expressing itself in language (see §§3.1–3.4). So the left hemisphere cannot ‘express itself in language’ either. The right hemisphere is not able ‘to disclose any experience of consciousness’ that we can recognize, because there is no such thing as a subordinate part of a human being being conscious. As will be argued in detail in chapter 3, it is only human beings (and other animals) who are conscious (or unconscious), and conscious of (or not conscious of) various things – not their subordinate parts. The left hemisphere is equally lacking in ‘any experience of consciousness’. Finally, the left hemisphere has no ‘verbal and ideational abilities’, although the verbal and ideational abilities of normal human beings are causally dependent upon the normal functioning of the left hemisphere.21
(2) The ‘self-conscious mind’ is not an entity of any kind
Second, the so-called self-conscious mind is not an entity of any kind, but a capacity of human beings who have mastered a reflexive language. They can therefore ascribe experiences to themselves and reflect on the experiences thus ascribed (see §14.6). But the ‘self-conscious mind’ is not the sort of thing that can