THE TIME TAKEN UP BY CEREBRAL OPERATIONS

Abstract

Mental states correspond to physical changes in the brain.The object of this paper is to inquire into the time needed to bring about changes in the brain, and thus to determine the rapidity of thought.When waves in the luminiferous ether of a particular length strike the retina a red light is seen, but a certain time passes after the waves have struck the retina before the light is seen:-(1) It takes time for the light waves to work on the retina, and generate in the cells a nervous impulse corresponding to the nature of the light; (2) it takes time for the nervous impulse to be conveyed along the optic nerve to the brain ; (3) it takes time for the nervous impulse to be conveyed through the brain to the visual centre; and (4) it takes time for the nervous impulse to bring about changes in the visual centre corresponding to its own nature, and consequently to the nature of the external stimulus."When these changes are brought about v. red light is seen.It does not take any time for a sensation or perception to arise after the proper changes in the brain have been brought about.The sensation of a red light is a state of consciousness corresponding to a certain condition of the brain.The chemical changes in a galvanic battery take time, but after they are brought about, no additional time is needed to produce the electric current.The current is the product of chemical changes in the battery, but at the same time the immediate representative of these changes; and the relation is so far analogous between states of consciousness and changes in the brain.Again, as it takes time to see a light, so it takes time to make a motion.Changes in the brain, the origin and nature of which we do not understand (physiologically they are part of the continuous life of the brain, mentally they are often given in consciousness as a will-impulse), excite the centre for the coordination of motions.The impulse there developed is conveyed through the brain (and it may be spinal cord) to a motor nerve, and along the nerve to the muscle, which is contracted in accordance with the will-iinpulse.We have here in the reverse direction the same four periods as in the case of a stimulus giving rise to a sensation.In each case there is the latent period in the senseorgan or muscle, the centripetal or centrifugal time in the nerve, the centripetal or centrifugal time in the brain, and the time of growing energy in the sensory or motor centre.Besides these

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