434 



ANNUAL REPORT SMITHSONIAN mSTITUTION, 1955 



worked out. Voluntary action is produced by nerve impulses that 

 originate within the brain and pass out along a succession of nerve- 

 cell nerve-fiber connections into the peripheral nerves and so to the 

 muscles which make movement by their contraction. 



We know something about how the sense organs in the eye, the ear, 

 the nose, and the skin transmute the stimuli of light, sound, floating 

 particles, and touch into afferent streams of nerve impulses. These 

 streams follow separate pathways into the brain to make possible the 

 functions of vision, hearing, balance, smell, and touch. These streams 

 of sensory impulses, which are like electrical currents, differ from each 

 other in that they have separate goals in the central nervous system. 

 The nerve cells in each goal, when activated, send on impulses into the 



CEREBRAL 

 CORTEX 



l.'i^^^o'^ 



VisoAL iSef/i. 



\ ^OOMA TIC 5EN&. 



Figure 1. — A schematic representation of the interconnection of neurone circuits between 

 the higher brain stem and the various functional areas of the cortex of both hemispheres. 

 These converging connections and the integrating mechanisms within the brain stem 

 make up the centrencephalic system. (From Penfield and Jasper, "Epilepsy and the 

 Functional Anatomy of the Human Brain," Little, Brown and Co., 1954.) 



neurone circuits which make possible conscious perception of things 

 seen or heard or felt. For example (see fig. 1), the visual pathway 

 leads from eye along optic tract (opt. t.) to visual center in the 

 occipital lobe of the cerebral cortex, but from there impulses pass on- 

 ward to play a role in the more complicated mechanisms of integration. 

 But what of the neurone mechanisms of consciousness? What of 

 thought, memory, behavior, and speech? Here the experimental 

 physiologist stops. He can help us little. Here we must consider the 

 brain and the mind of man himself. It is true that Pavlov and otliers 

 have thrown some light upon the parts of the brain used in animal 

 behavior, and in learning, by study of the conditioned reflexes. But 

 this takes us such a short way toward the basic understanding that we 

 seek. 



