68 K. S. LASHLEt 



II. THE RELATION OF CEREBRAL INJURY TO THE GENERAL ACTIVITY 



OF THE RAT 



Various disturbances in the general activity of animals suffer- 

 ing from cerebral lesions have been described, such as restless- 

 ness in frontal cases or inertia and loss of emotional reactions 

 after occipital injury. Although such changes have not been 

 worked out carefully enough so that we may predict their occur- 

 rence after any given operation the possibility of their existence 

 in operated animals complicates the study of the effects of 

 cerebral lesions upon learning. Measures of learning ability 

 of partially decerebrate animals based upon the rate of forma- 

 tion of a motor habit may be deceptive owing merely to dif- 

 ferences in the general activity of the animals. The compli- 

 cated problems which are adapted to the study of habit-forma- 

 tion in animals all demand the solution of some problem by 

 overt trial and error and the fixation of certain parts of the 

 reaction in habit. Theoretically, every animal must solve the 

 problem at every trial so that differences in the amount of 

 activity will make no difference in the amount of practice ex- 

 pressed in a given number of trials. But other factors besides 

 frequency are instrumental in determining the rate of learning 

 and among these the temporal element is of fundamental im- 

 portance. The slow or inactive rat will require a longer time 

 per trial than will the active one. Perhaps he will thus gain 

 the advantage of distributed practice and thus learn with less 

 effort; perhaps delays between the acts of the series to be asso- 

 ciated will prolong the process of association as they do in the 

 formation of the conditioned reflex. We have no means of 

 determining, at present, what the real influence of such con- 

 ditions will be. It becomes necessary, therefore, to control 

 the general activity of the animals carefully, or where this is 

 impossible, to determine the existence of individual variations 

 in general activity so as to avoid the mistake of ascribing to 

 specific cerebral injuries effects which are due merely to general 

 ill health, or of interpreting slow learning as due to loss of prob- 

 lem-solving ability or to slowed rate of reintegration when its 



