4 K. S. LASHLEY 



the frontal lobes,^ have failed, and we can only say that the 

 complexities of behavior which we term intelligence are some- 

 how a function of the activities of the entire cerebrum. It 

 is yet an open question as to whether the more complex types 

 of behavior result from a mere multiplication of reflex and 

 conditioned reflex paths or involve some fundamentally differ- 

 ent mechanism from those with which the study of spinal 

 reflexes has made us familiar. In many respects the reflex 

 theory seems inadequate to account for the larger number 

 of human and animal reactions, yet our knowledge of neural 

 functions is as yet so slight as to make the formulation of 

 any plausible alternative hypothesis impossible. 

 \ Many phenomena of behavior seem explicable only in 



terms of a dynamic function of the central nervous system 

 for which the conceptions both of the conditioned reflex and 

 of a mosaic arrangement of faculties are inadequate. Reac- 

 tions to ratios between stimuli, to spacial and temporal rela- 

 tionships — in fact, most of the adaptive behavior of the or- 

 ganism — demand a mechanism in which dynamic as well as 

 integrating functions may be exercised. Much of the recent 

 direct evidence on cerebral mechanisms also points to a func- 

 tional unity rather than a mosaic arrangement in activities 

 within the larger functional divisions so that the problem of 

 mass relationships in neural function takes on a more impor- 

 tant aspect than is implied in either the theory of conditioned 

 reflex arcs or in that of localized faculties. 



It has seemed important, therefore, to carry through a 

 series of experiments designed to test the relative significance 

 of functional localization and of the factor of total mass in 

 the performance of various types of activity. In an earlier 



'Bianchi ('22) has claimed that the learning function is restricted to the 

 frontal lobes in primates and has reported experimental evidence in support of 

 his view. Mr. Carlyle Jacobsen and the writer are now repeating his experi- 

 ments on rhesus monkeys with the addition of quantitative measures of the 

 rate of learning. We have been unable to verify his findings on a single point. 

 In fact, removal of the entire frontal and parietal association areas has not 

 resulted in any measurable retardation in the rate of formation of complex 

 sensory or motor habits. 



