We might liken the mind to the boiler in which steam is generated, and the body to the engine which the steam runs. If the boiler bursts, the engine stops; but it may not be otherwise damaged. It simply cannot carry out its main function of motion any longer. The fires under the boiler are still burning and can be kept burning so long as fuel is provided, but the connection is broken and the great bulk of iron is a useless thing in that it can no longer fulfil its purpose.
In just such a way may the mind be paralyzed; but the spark of life, which has through all the years kindled the now lost mind to action, may still remain—a useless thing, which would die away if not tended from without by other bodies whose minds are still intact.
But in the demented mind consciousness still remains, the awareness of the young child or baby stage of life. The connection between the upper or conscious brain centers and the body has been tampered with; it no longer is direct, but breaks off into switch-lines. But the contact still holds between the lower or unconscious mind and the body; so the automatic body functions go on, directed as they were in babyhood before the independent mind assumed control. Hence, when all acute consciousness is finally gone, the unconscious mind, a perfect automaton, may still carry out the simplest vegetative activities of existence.
When body is dead, mind, so far as its reactions to the world we know are concerned, ceases to act. But when the conscious mind is “dead” the body may yet live as a vegetable lives, with all its distinctively human functions lost. Motionless, save for the beating of the heart and the reaction of the lungs to air, the body may still be alive, though the mind long since has ceased all earthly activity.
So we discover that an organ of mind is an essential, here, to life of mind, and that mind only can induce this organ to any action above the vegetative stage. But, on the other hand, we find that life can exist without conscious mind, even if untended by others, for a limited time.
If the direct nerve connections between the brain and the hand, the brain and the foot, or the brain and the trunk are cut off, the mind henceforth realizes nothing of that part except as the sense of sight reports upon it; for the optic nerves relate the hand and mind, through this sense, as truly as the motor nerves which carry the mind’s message for motion to the hand, and the sensory nerves which carry back to the mind the hand’s pain. But let the optic nerve be inert, the sensory and motor connections broken between brain and hand, or foot and trunk, or brain and trunk, and the hand or foot may be amputated and the mind never sense the fact; the trunk may be severely injured and the mind be serenely unconscious. So the brain in man is “the one immediate bodily condition of the mental operations.” Take away all the brain and man’s body is a useless mass of protoplasm.
The brain’s varied and intricate nerve connections with all parts of the body, through nerves branching from the main trunks in the spinal cord, we shall not discuss, for you know them through your study of anatomy. For the purpose of our psychology we need consider only two of the main divisions of the brain—the cerebrum, which includes what we call the right and left hemispheres, and the cerebellum.
The Cerebrum or Forebrain
For convenience the various lobes of the cerebrum are known as frontal, temporal, parietal, and occipital, according to the parts of the brain referred to: as forehead, temples, crown, or occiput. The cerebellum, or hind brain, is also divided into two hemispheres, and is situated behind and below the hemispheres of the cerebrum.
A system of localization has been roughly mapped out, the result of careful laboratory work on animals and of studying the loss of various functions in human beings as related to the location of brain injuries.