INTEGRATION OF ACTIVITIES 



161 



directly responds. It is not unlikely that an impulse arriving at a 

 synapse from an axon produces an activating substance so that the wave 

 is initiated anew in the adjoining dendrite, while an impulse going back- 

 ward over a dendrite to a synapse produces an inhibiting substance so 

 that further propagation is prevented. 



Fig. 125. — Functional areas of human cerebrum. Above, lateral surface from left 

 side. Below, median surface viewed from left. The olfactory area, because it is dis- 

 continuous, is dotted. All boundaries are only approximate. 



Localization in Brain. — It is more difficult to ascertain the function of 

 different parts of the brain than to determine the role of nerves, because 

 those parts cannot be isolated and experimented upon wholly separately. 

 Knowledge of the regions where different brain functions are performed 

 comes from destruction of certain areas in laboratory animals, artificial 

 stimulation of brain areas in anesthetized animals, the consequences of 



