224 BRAINS OF RATS AND MEN 



In primates, extrapyramidal fibers may retain and 

 indeed amplify the specific relationship to visual re- 

 flexes which is so obvious in the rat, and this visual- 

 motor cortex is electrically excitable. It has been 

 shown that, though electrical stimulation of points in 

 the occipital and frontal (premotor) lobes of the pri- 

 mate brain is followed by movements of the eyes, 

 nevertheless this movement requires about twice as 

 much time as that evoked by stimulation of the 

 oculomotor centers in the precentral cortex. No mo- 

 tor projection fibers enter the pyramidal tract from 

 these other excitable areas, nor is the longer time re- 

 quired for the response from these areas due to the 

 transmission from them to the precentral motor cor- 

 tex, for if the latter is destroyed by the excision of the 

 frontal pole of the hemisphere the motor response is 

 still present. The extrapyramidal oculomotor sys- 

 tem is evidently physiologically different from the 

 pyramidal system, being apparently more directly 

 concerned with certain cortical reflexes. 



In the following discussion our attention will be 

 directed especially to the phasic activities of the 

 cortex, to intentional control of behavior, which, as 

 already pointed out, differs from the tonic control in 

 that the intrinsic cortical mechanisms are competent 

 to redirect the "natural" course of the innate and 

 habitual behavior sequences in patterns not previous- 

 ly organized and stabilized. 



Lashley (1924) has shown that surgical removal of 



