Page:Popular Science Monthly Volume 35.djvu/403

Rh fibers, make up the convolutions of the brain and constitute the physical basis of the mental life.

The voluntary or spontaneous excitation of ideas is thus to be attributed to the activity of the psycho-motor centers, while the inhibitory centers, since they play an important part in attention and concentration of thought, are the seat of the higher faculties; and intellectual power probably bears a direct ratio to the development of these centers. By observations and experiments similar to those employed in localizing the sensory and motor areas, the inhibitory centers have been localized in the frontal lobes of the brain. The development of these lobes, as compared with other parts of the brain, is conspicuous in man; as a rule, also, great intellectual power is associated with great frontal development.

The biological doctrine that automatism is a property of protoplasm supports the theory of the originally spontaneous character of the so-called voluntary movements, leading up to the view that volition is an underived quality of mind; but it is a biological fact that muscles and nerves appear on the stage of animal life together in the form of a reflex apparatus, and that the primordial movements executed by these specialized forms of protoplasm are reflex; my fifth thesis is, therefore, that the germs of volition are to be found in movements; that volition, so far from providing an original stimulus to the muscular activities, has itself grown out of these activities—the voluntary movements developing secondarily from reflex ones.

Movements in themselves excite agreeable sensations which prompt to repetition; such as prove injurious, however, become a source of pain which tends to their suppression—that is, to inhibition; volition, therefore, develops under the stimulus of pleasure combined with the repressive influence of pain, both of which result from the action of muscles. The will is thus disciplined and directed to such activities as are useful to the organism.

Prof. Meynert describes volitional impulses as due to the [revived] perception or memory of sensations of innervation. By means of association these memories acquire sufficient intensity themselves to excite movements which thus starting from the brain appear to be spontaneous; their character will, however, depend on what has been previously registered in the motor centers. Although the brain-centers concerned in the exercise of voluntary restraint (the inhibitory centers), primarily stimulated to activity by the pain resulting from injurious movements, do not