LASHLEY— CEREBRAL FUNCTION 269 



cient number of fibers previously integrated in tbe habit to produce the 

 conditioned reflexes, in spite of the great destruction of other fibers of 

 equivalent function. Such a possibility is supported by data on other 

 functional areas in which the various parts seem equipotential ( Franz, 4:: " 

 Lashley 34 ) and by the apparent equipotentiality of parts of tbe motor 

 area revealed by electrical stimulation (Lashley 44 ). but several facts 

 speak strongly against this explanation. 



Partial destructions usually entail a certain confusion in the per- 

 formance of all the functions of an area, which seems to exceed any- 

 thing of the sort noted in these animals. 4 "' 



In Number 3, the destruction on both sides was so nearly complete 

 that only a part of the face areas could have remained functional. 

 If we attempt to explain the survival of habits as being due to the 

 activity of undestroyed parts of the motor area, we must assume that 

 a part of the face area is capable of performing all the functions of the 

 entire motor cortex — an assumption which is as far from the accepted 

 views of localization as is the denial of all habit function to tbe motor 

 areas. 



2. It might be urged that in the recovery from the motor paralysis, 

 the vicarious functions assumed by other areas included the movements 

 involved in the problem-box habits ; that the habits were relearned dur- 

 ing the period of recovery from paralysis. The habits, how r ever, con- 

 sist of particular patterns of movement associated with the stimuli 

 presented by the latch boxes. During the postoperative period, there 

 was no occasion for the animals to reacquire these particular patterns 

 of movement and no opportunity for the movements to be associated 

 with the latch boxes. 



3. The long controversy concerning the sensorimotor function of 

 both the precentral and postcentral gyri suggests that the two may both 

 include centrifugal cells for the performance of habits. The literature 

 cited in the first part of this paper seems to establish the differential 

 function of the two areas, however, and the lack of paralysis after 

 lesions to the postcenral gyrus makes the hypothesis untenable. 



43a. Franz, S. I.: On the Functions of the Cerebrum: The Frontal Lobes, 

 Arch. Psychol, 1907. No. 2, pp. 1-64. 



44. Lashley, K. S. : Temporal Variation in the Function of the (iyrus Pre- 

 centralis in Primates, Am. J. Physiol. 65:585-602, 1923. 



45. I am collecting data on this question at present. The evidence is not 

 complete, but there is indication that. e. g., any extensive but incomplete 

 destruction of the visual areas of both hemispheres in the rat is followed by 

 inaccuracy of brightness discrimination, with great variability from day to 

 day, such as has been reported by Franz in 1916 for aphasia, yet without any 

 complete loss of any phase of the visual function. Such loss as appeared in 

 the motor hahits of the monkeys was almost certainly ascribable to the simple 

 motor weakness, and gave no indication ol an apraxia. 



