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what became physiology and neuroscience. Furthermore, by associating the psychological capacities of humans with the pineal gland, he had moved consideration of their physical dependence from the ventricles (filled now with particles of the animal spirits rather than with the psychic pneuma of Galen) to the matter of the brain – in his case the pineal gland. This shift of attention from the ventricles to the substance of the brain became definitive as a result of the work of a young man who was but twenty-nine when Descartes died, Thomas Willis.

      1.3 The Cortical Doctrine of Willis and Its Aftermath

       Thomas Willis: the basis of psychological functions in the cortex

       Animal spirits from the cortex activate muscles through the nerves

      The role of the animal spirits in integrating the activity of the cortex and the movement of muscle is then spelled out:

      We have shown that the Animal Spirits are made in the cortex of the brain and cerebellum, whence they descend and flow into the middle and marrowy parts where they are kept in sufficient amounts to be used for the various purposes of the Soul. Animal Spirits flow from there to the oblong and spinal marrow, and thence into the nerves and nervous shoots, activating and expanding these. Finally, sufficient amounts of Animal Spirits are distilled from the ends of the nerves implanted in the muscles, membranes and viscera, and so activate them, the organs of sense and motion. (ABN 24)

       In brutes, the cortex lies in a reflex arc from sensation or perception to motor act

      How is the flow of the animal spirits in and from the cortex to muscles initiated? To answer this, Willis first describes how the flow of animal spirits occurs in the brain when an organ of perception is excited (ABN 38). He then links an animal’ s perceiving something with a subsequent motor act. This description places the cortex in a reflex arc from sensation to motor act, and it is clear that Willis thought that in all animals other than man all motor acts are reflex, for he comments that ‘because brutes or men, whilst they as yet know not things, want spontaneous appetite. So long therefore, they being destitute of the internal principle of motion, move themselves or members, only as they are excited from the impulse of the external object, and so sensation preceding motion, is in some manner the cause of it’ (ABN 59). The reflex nature of many motor acts is emphasized in his comments on the behaviour of some animals when they are cut in pieces (ABN 17).

       Human acts of will are possible due to interaction of soul and body in the cortex

      So, volitional acts are initiated by the rational soul, located in the corpus callosum, after the animal spirits have delivered ‘the images or representations of all sensible things’ from the common sensory:

      Willis then associated the functions of perception, memory and volition with the cerebral cortex. In particular he associated these functions with the gyri of the cortex, so that animal spirits move between the gyri. The gyri, he held, were much more numerous in humans than in other animals because of the superior intellectual powers of human beings (ABN 65–8).

      Willis explicitly subscribes to the Cartesian idea of an immaterial soul or mind, that perceives and performs acts of will initiating motor action and that interacts with the body. Like Descartes (and many others), he held that because the rational soul is immaterial, therefore it has no parts. Having no parts, it is indestructible, for all destruction is decomposition into parts. The important difference between Willis and Descartes is that Willis locates the point of causal interaction between the mind or rational soul and the body in the cortex – namely, in the corpus callosum – and not, like Descartes, in the pineal gland, incorrectly located in a ventricle. However, just as Descartes was left with the insoluble problem of explaining the interaction of the mind with the pineal gland, so Willis was left with the problem of the explaining the interaction between the immaterial rational soul and the material corporeal soul in the corpus callosum. So no explanation is provided as to how the bond is formed between the rational soul and the corporeal soul, which are placed in a state in which they can interact by God at birth: ‘That this immortal soul (the Rational Soul), for as much as it cannot be born, as soon as all things are rightly disposed for its reception, in the humane formation of the child in the womb, it is created immediately of God, and poured into it’ (ABN 41f.).

      The cortex 100 years after Willis

      The revolution due to Willis ultimately led to a focus on the relationship between the cortex and those nerve trunks that could be argued to be intimately related to it. For the century after Willis there was no advance regarding the problem of functional localization in the brain. In 1784 Jiri Prochàska (1749–1820) did not go much beyond Willis:

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