Philosophical Foundations of Neuroscience. P. M. S. Hacker
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(3) Incoherence in Eccles’s hypothesis
Third, Eccles’s main hypothesis is unintelligible. If the self-conscious mind were, per impossibile, ‘actively engaged in reading out’ from areas in the dominant hemisphere and ‘selecting from these modules according to attention’, then the self-conscious mind would have to perceive or be aware of the neural modules in question (otherwise how could it ‘read them out’?), and know which ones to select for its purpose (otherwise the wrong ones might constantly be selected). Or, to put matters more lucidly, for any of this story to make sense, human beings would have to be aware of the neural structures and operations in question, and, from moment to moment, decide which ones directly to activate, and, of course, have the capacity to do so. But we possess no such knowledge and no such capacity.
(4) The very notion of the self-conscious mind presupposes the unity of experience
Finally, it is confused to suppose that the raison d’être of the ‘self-conscious mind’ is to engender the unity of the self and, as our contemporaries would put it, ‘solve the binding problem’. For any talk of a person or of a human being as having a mind already presupposes the unity of experience and cannot be invoked to explain it.
Eccles’s errors cannot be rectified by substituting the brain for his conception of the ‘self-conscious mind’
Eccles’s dualism was misconceived. Contemporary neuroscientists are eager to dissociate themselves from his doctrines and to dismiss his ideas as silly. This is misguided. Eccles had the courage to face difficult problems and to pursue his ideas about them to their logical conclusions. That his ideas are wrong is true, and much can be learned from the errors in question. It is, however, a sad mark of how little many neuroscientists have learned from Eccles’s struggles that they apparently believe that the problems that Eccles’s interactionist dualism was designed to answer can be solved by substituting the brain for Eccles’s ‘self-conscious mind’. Problems regarding how the mind can bring about movements of the muscles and limbs by acts of will are not solved by supposing, as Libet does (see §9.2), that it is the brain that decides what muscles and limbs to move. Although it is misguided to suppose that the mind is in liaison with the left hemisphere, it is no less misconceived to suppose, as do Sperry, Gazzaniga and Crick (see §17.3), that the hemispheres of the brain know things, have beliefs, think and guess, hear and see. For these are functions of human beings and other animals, not of brains or half-brains (which enable human beings to exercise those functions). And, as we have noted, although it is confused to suppose that the mind scans the brain, it is equally confused to suppose that the brain must scan itself in order to generate awareness or self-consciousness – as if it lay in the nature of self-consciousness that it necessarily involves a self-scanning process, if not of the mind, then of the brain. In short, the lessons that can be learned from Eccles’s failure have largely yet to be learned. We shall endeavour to show this in some detail in later chapters.
2.4 Wilder Penfield and the ‘Highest Brain Mechanism’
Penfield’s training
Wilder Penfield (1891–1976) was born in Spokane, Washington. After graduating from Princeton in 1913, he won a Rhodes Scholarship to Oxford and entered the School of Physiology there to begin his medical studies under the inspiring influence of Sherrington. He followed Sherrington’s interest in histology and, in particular, in neurocytology. After obtaining his BA in physiology at Oxford, he went to the Johns Hopkins Medical School, where he finished his medical degree in 1918. His first research concerned changes in the Golgi apparatus of neurons after axonal section. In 1924 he began to study the healing processes of surgical wounds in the brain. On Sherrington’s advice, he spent some time in Madrid working with Pio del Rio-Hortega, learning to use the histological methods of his brilliant teacher Ramón y Cajal. To this end, surgical specimens of brain scars were collected from patients who had been operated on for post-traumatic epilepsy.
Penfield’s achievement
Penfield was aware of the studies on cortical localization in the primate brain that Sherrington had carried out, and which have been described above. In 1928 he went to Breslau to work with Otfrid Foerster, to learn his method of gentle electrical stimulation of the cortex of epileptic patients while they were under local anaesthesia during the excision of epileptogenic scar tissue. During these procedures he learned the method of operating under local anaesthesia, using electrical stimulation to identify the sensory and motor cortex to guide the surgical excision. This technique was to be used to singular effect by Penfield in Montreal, where, in 1934, he established the famous Montreal Neurological Institute at McGill University, which was devoted to the study and surgical treatment of focal epilepsy. Such stimulation made it possible to locate exactly the position of the sensorimotor cortex and of the cortex subserving speech, so that these vital areas could be spared during the surgical excision. In some instances the stimulation might activate the more excitable epileptogenic cortex and reproduce a portion of the patient’s habitual seizure pattern. This enabled the surgeon to identify the site of the physiologically deranged epileptic focus. Penfield’s mastery of these procedures was subsequently summarized in a series of monographs on brain surgery for epilepsy.
Penfield noted in 1938 that stimulation of certain parts of the temporal cortex in patients occasionally excited the vivid recall of previous experiences. It became evident that almost half of the patients afflicted with epilepsy had seizures that could be shown to originate in one or other of the temporal lobes. This work on temporal lobe epilepsy led to very important observations regarding the hippocampus and memory function, as well as the localization of the cortex subserving the latter. By 1951 Penfield, together with Milner, had shown that removal of one hippocampus on the medial aspect of the temporal lobe resulted in severe memory disorder in patients who were later found to have damage to the hippocampus on the opposite side. Thus the bilateral loss of function of the hippocampus led to the complete inability of these patients to remember any post-operative occurrence. This memory loss was not accompanied by any loss of intelligence or attentive capacity. Penfield’s analyses of the electrical stimulation of the cortex of 1,132 conscious patients undergoing brain surgery greatly extended our knowledge of functional localization, especially with regard to memory and to that most human of capacities, speech.
Penfield’s methodological commitment
Already in his student days, Penfield had had a ‘sense of wonder and a profound curiosity about the mind’. When he turned from the study of the animal to the human brain, his ‘planned objective’, he later wrote, was ‘to come to understand the mechanisms of the human brain and to discover whether, and perhaps how, these mechanisms account for what the mind does’.22 Studying under Sherrington, he came to ‘the realization that the brain was an undiscovered country in which the mystery of the mind of man might someday be explained’. He was, of course, fully aware of Sherrington’s views on the relation of mind and brain. In the final paragraph of the foreword to his great book The Integrative Action of the Nervous System (1906), Sherrington had remarked, ‘That our being should consist of two fundamental elements offers, I suppose, no greater inherent improbability than that it should rest on one only.’ Penfield, however, took the view that the neuroscientist should endeavour to explain the behaviour of animals, including humans, on the basis of neuronal mechanisms alone. Only if that failed, he thought, should one have recourse to alternative forms of explanation. And throughout his career as a neurosurgeon, he retained this methodological commitment.
Penfield on the mind
Towards the end of a long life dedicated to neurosurgery and neurology, Penfield published a small volume entitled The Mystery of the Mind. This was, he wrote, ‘the final report of my experience’ – an overview of what he had achieved in respect of his youthful objective. ‘The nature of the mind’, he averred, ‘presents the fundamental problem, perhaps the most difficult and most important of all problems’ (MM 85). What he wished at last to do, he wrote in the preface, was to ‘consider the evidence as it stands, and ask the question