THE FRONTAL LOBES 225 



the electrically excitable cortex of monkeys is fol- 

 lowed by temporary motor deficiency with great 

 weakness, from which, however, there is nearly per- 

 fect recovery within a few weeks. Complicated prob- 

 lem-box habits acquired before the operation are 

 found to be but little impaired after full recovery from 

 the effects of the operation. These very important ob- 

 servations and similar ones made by others, as well 

 as clinical observations on human cases, necessitate 

 some recasting of formerly prevalent views of cortical 

 functions, especially the part played by the excitable 

 areas. 



Lashley's conclusion is that this cortex in all 

 animals is part of the kinetic mechanism for reflex 

 control of posture and for maintenance of excitability 

 of lower motor centers. He believes that 



a normal function of the stimulable cortex is to supply a sub- 

 stratum of facilitating impulses which act in some way to render 

 the final common paths excitable by the more finely graduated 

 impulses, descending from the cortex by extrapyramidal paths 

 and producing the finer shades of adaptive movement. In other 

 words, impulses descending from the precentral gyrus do not 

 initiate the finer adaptive movements through the lower motor 

 neurons, but only "prime" these cells so that they may be excited 

 by impulses from other sources [1924, p. 274]. 



This way of looking at the matter seems to be 

 justified by the facts which Lashley brings forward in 

 support of it. But there are other factors which do 

 not fit into this scheme. In rats, destruction of the 



