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This subject is discussed with great care in Professor H. Calderwood’s The Relations of Mind and Brain, with the result that a series of facts are established which I do not remember seeing brought out as convincingly anywhere else. The chief value of his book lies in the proof which it leads of the following positions, which I set here in order, with reference to passages in which they are discussed:—

1. That the primary function of the brain is to serve, not as an organ of thought, but as an organ of sensory-motor activity (pp. 196, 290, 302–307, 2nd ed.).

2. That, as demonstrated by experiment, by far the greater part of the brain—if not all—is monopolised for sensory-motor work, 431leaving little, if any, of it to be employed for other purposes (pp. 302, 361).

3. That in the comparison of animals there is no fixed ratio between degree of intelligence and complexity of brain structure—a highly developed and convoluted brain finding its chief explanation in “ the much more complex muscular system to be controlled “(p. 149). “Advance in intelligence and advance in complexity of brain structure do not keep pace with each other; they are not correlated so as to harmonise” (p. 148). The dog, e.g., with a brain less elaborate in its convolutions, shows a higher degree of intelligence than the horse, with a more ample and complicated series of foldings in the convolutions of the grey matter. A number of leading cases are examined in detail in Chap. v. “Comparison of the Structure and Functions of Brain in Lower and Higher Forms of Animal Life” (pp. 123ff.). Cf. pp. 260, 261.

4. That the view that special cells are appropriated to mental functions,—as, e.g., the “mind-cells” of Hacokel (pp. 298–303), or the memory-cells of Professor Bain (pp. 356–364),—is not borne out, but is discredited by physiology. As against Haeckel, it presents “a cumulative body of evidence adverse to the hypothesis that human intelligence can be attributed to the giant pyramidal cells abounding in the fourth layer of the brain. All available evidence favours the conclusion that these giant cells are motor cells largely concerned in the functions of co-ordination of related intra-cerebral movements. It thus seems warrantable to infer that such co-ordinated movement takes rank as the highest function of brain. In accordance with this view is Dr. Ferrier’s conclusion as to the frontal regions in the human brain, based on the whole range of experiments under electromotor excitation, “that they are ‘inhibitory motor-centres’ such as may be associated with an exercise of attention” (pp. 302, 303). As respects Bain’s theory, “the known laws of cerebral activity do not favour such calculations as are suggested by Professor Bain. The space appropriated for the sensory and motor functions includes a great part of the mass of cellular tissue” (p. 360, see proof in detail). Generally, “physiology does not discover any new function in the higher part of the system, except more detailed ordination” (p. 297). “We must regard equally the frontal and the occipital regions of the grand central organ as concerned with sensory-activity and correlated motor-activity “ (p. 316).

5. That the true relation of mind and brain lies in the dependence of the former on the latter in sensory functions, and in the use made by the former (involved in all forms of mental activity) of the brain’s motor functions. The following is an enumeration of forms of brain action which must be considered as generally attending on the more ordinary mental exercises: “(1) Action of the special senses, and of the more general tactile sense; (2) action of the muscles concerned in the management of these senses, and specially of the organs of sight; (3) co-ordination of sensory and motor apparatus required for use of the senses; (4) action of sensory centres consequent on use of imagination (p. 357), in part a renewal of sensory impressions, 432or a movement of sensory cells consequent upon stimulus which imagination supplies; (5) sensory and motor action consequent upon the stimulus coming from mental emotion, such as weeping, facial expression of sadness or sympathy . . . all these phases of brain action, as they involve active use of brain energy, imply transformation of energy, consequent waste of brain substance, and inevitable sense of exhaustion. . . . First, there is large use of both sensory and motor apparatus in connection with all the ordinary forms of intellectual activity. Second, all thought proceeds, to a large extent, by use of language, and thus seems to involve activity of the cells concerned with the acquisition and use of language and speech. Third, concentrated thought makes a severer demand upon all the forms of brain action connected with ordinary thought, and so quickens and increases the exhaustion of nerve energy” (pp. 412–415). This defines the sense in which the brain is the organ of mind, and shows that it is not the organ of mind in the same sense in which it is a sensory-motor organ (p. 315).

6. That while the mind is thus manifoldly correlated with brain action, not only are mental-facts, as the highest authorities admit, absolutely distinguishable from brain-facts (pp. 292, 293, 314, 315); but the mental phenomena in man (even in sensation and consciousness of succession in sensations, in memory, language, still more in the higher mental functions, self-regulated voluntary activity, intellectual activities, thought on ultimate questions of existence, etc.) transcend brain action altogether, and are non-interpretable through it (pp. 304–307, 366, 367, 385–396; Chap. xv. “The Higher Forms of Mental Activity”). “Mind transcends all the sensibilities of our organism. The whole range of our thoughts,—as we interpret events under the law of causality, form conceptions of rectitude, and represent to ourselves a scheme of the universe as a whole,—transcends all the functions of the nerve system. Known facts are in accordance with this duality; paralysis of a cerebral hemisphere may leave intelligence unaffected; though high intellectual life involves good brain development, high brain development does not necessarily involve a distinguished intellectual life; but the more highly educated a man is, so much the more does his life transcend what his bodily functions can accomplish” (p. 307).

The result reached is—“that the intelligence of man, as known in personal consciousness, is of a nature entirely distinct from sensory apparatus, its functions being incapable of explanation in accordance with the laws of sensory activity. . . . The facts of consciousness lead to the conclusion that mind is a distinct order of existence, different in nature from the nerve system, differing in the mode of its action from the mechanical action of sensory apparatus, and capable of interpreting the rational sensibilities of our organism, so as thereby to discover a rational order in things external, or adaptation of related things in nature to rational purpose” (p. 307).

In establishing these positions, Professor Calderwood at the same time refutes certain others, viz.:—

1. The theory which identifies mind with brain action (pp.313, 314).


2. The theory which supposes that there is an exact correspondence between the mental and physical facts,—or that, as Bain and Spencer put it, they are but two sides of the same thing (pp. 293–296). “That thieve is an absolute harmony involving a parallelism or correspondence, and making an exact equation of both organic and non-organic activity in all cases, it is quite impossible to maintain “ (p. 316).

3. The theory that mental phenomena can be translated into the language of brain changes, or expressed in terms of the motions, groupings, or electric discharges of the latter (pp. 314, 315).

4. The view that mind does not act on the brain series to alter or modify it—“that action and reaction of nerve tissue carries the explanation of all that belongs to human life” (pp. 326–343). “It was inevitable that a theory reducing all human action to the play of nerve force should be propounded” (p. 336); but “(l) There is neither anatomical nor physiological evidence in support of the theory. . . . (3) The facts relied on as auxiliary to the theory do not in reality support it. . . . (4) The facts to be explained—voluntary control of muscular activity under guidance of intelligence—do not manifest resemblance to the known facts of nerve action, but present a decided contrast” (pp. 328, 329).

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