LASHLEY— CEREBRAL FUNCTION 255 



The first of these views is definitely ruled out by the evidence cited 

 above for habit formation after destruction of the areas. The evidence 

 for the second and third views, as applied to primates, is inconclusive, 

 although a considerable mass of evidence derived from the cerebral 

 paralyses seems to support the second. The validity of this evidence 

 will be considered after the experimental data are presented. 



A simple test of the hypotheses is possible. If after total destruc- 

 tion of the precentral areas an animal shows undiminished ability to 

 carry out activities of all degrees of complexity, acquired before the 

 operative destruction, this will be conclusive evidence that the lesion 

 did not destroy any part of the conditioned reflex arcs involved in the 

 activities, and, as a corollary, that these arcs do not traverse the motor 

 areas. Loss of the conditioned reflexes following the lesion with their 

 later reestablishment through training will support the second view, that 

 the pyramidal cells of the precentral region are the principal efferent 

 paths involved in habitual movements. 



Such a test was made with the rat and gave unmistakable evidence 

 against the participation of the motor areas in the activities of the 

 simple maze and visual discrimination box ( Franz and Lashley, ; 

 Lashley 37 ). Since the publication of that report, the results have been 

 confirmed for a complex maze and the "double-platform box." As the 

 rat shows no paralysis after lesions to the stimulable areas alone, it is 

 not possible to generalize from it to higher forms which do develop a 

 paralysis. I have therefore repeated the tests in a series of experiments 

 with monkeys. 



EXPERIMENTAL METHODS 



The parlysis which follows lesions to the precentral gyrus in monkeys 

 necessitates a modification of the technic used with the rat. The general 

 procedure was as follows : The animals were trained in rather simple 

 manipulative acts involving a new and easily recognizable pattern and 

 sequence of movements. They were then kept without practice for 

 about two months, at the end of which time their retention of the habits 

 was tested. This gave a measure of the normal loss to be expected 

 from disuse of the habits over a period equal to that required for 

 recovery from cerebral paralysis. After these preliminary retention 

 tests, the motor areas were destroyed. The animals were then kept 

 without further practice in the habits until the paralysis was so far 

 improved that they were judged capable of making the movements 

 required. They were then given a final series of retention tests (post- 

 operative retention tests) and brought to necropsy. 



Train ing Methods. — For training, the familiar problem-box method 

 was used. The animals were confined in a large cage. 5 by 5 feet, to 



