532 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



except by abnormal conditions in the brain itself, only by the dis- 

 charge of sensory nerve impulses into the brain cortex. Troland 

 (1926) believes that consciousness is generated in the nerve associa- 

 tion centers (synapses) that occupy most of the cortex. However, 

 we do not locate our feeling of consciousness in the brain. A pain, 

 for example, is felt at the point of physical injury, but if the nerves 

 to the brain are deadened by an anesthetic we do not feel a surgical 

 operation or the pulling of a tooth. In the same way our other sen- 

 sory perceptions are projected to the objects or conditions that stimu- 

 late the sense organs. Consciousness is the perception of what we 

 see, hear, or feel. Yet the brain action, whatever it may be, is essen- 

 tial to the conscious sensation. 



Human consciousness, then, is merely a mental experience gen- 

 erated in the brain by nerve impulses from the sense organs. A nerve 

 impulse is a wave of metabolism propagated through the nerve, ac- 

 companied by an electrical disturbance, and is the same from what- 

 ever sense organ it is engendered. The nerve structure may be 

 adapted to its function, but the resulting form of consciousness de- 

 pends on the particular brain center to which the nerve goes. Our 

 conscious perceptions correspond with the varieties of sense organs we 

 possess. 



Our ordinary state of consciousness, when nothing disturbs us, is 

 the sum of all sensory impressions external and internal received at 

 any one time. If the sensory nerves gradually cease to convey mes- 

 sages, we fall asleep and consciousness disappears. 



With most of us awareness of our surroundings seems so real that 

 we cannot doubt the reality of consciousness, if only as a sensation. 

 Surely, pain, fear, anger, pleasure are states of consciousness that 

 may induce muscular movements, but few of us can be convinced 

 that our everyday acts are not consciously dictated. Yet we do not 

 Imow how we perform actions that we ascribe to intent. Picking 

 up a pencil from the table, for example, seems to be a perfectly simple 

 voluntary act, but the human arm, shoulder, hand, and fingers con- 

 tain more than 40 muscles, and we do not know what muscles we use, 

 or how they are stimulated and coordinated in action to carry out 

 the dictates of our "will." 



Though we must admit, then, that consciousness is real and is some- 

 how a product of brain activity, by no effort of the imagination can 

 we understand it. As said by Sperry (1952) : "Despite steady ad- 

 vancement in our knowledge of the brain, the intrinsic nature of mind 

 and its relation to cerebral excitation remains as much an enigma 

 today as it was a hundred years ago." The histologists have found 

 no correlation between the histological structure of the brain centers 

 and the conscious sensations aroused in them. As noted by Sperry, 

 "Present-day science is quite at a loss even to begin to describe the 



