124 K. S. LASHLEY 



destruction of the frontal or occipital regions abolishes corre- 

 sponding habits that under normal conditions the various parts 

 of the cerebrum have specialized functions. Nevertheless this 

 specialization is only relative and is of such little practical con- 

 sequence that learning may go on with equal speed in the pres- 

 ence or absence of the specialized areas. 



The results further form a strong argument against the exist- 

 ence of any cerebral areas which have a directive influence over 

 learning, whether it be by "attention," mediated through the 

 frontal lobes or by the "conscious action" of the brain as a whole. 

 On the contrary, they suggest that the only essential condition 

 for learning is the simultaneous activity of two reaction systems 

 which are in anatomical connection by association fibers. 



By far the most suggestive of the results brought out by the 

 \ experiments are those dealing with the function of the occipital 

 L~pole and the corpus striatum. It is clear that the habit involv- 

 ing discrimination of brightness has no other cortical representa- 

 tion than the occipital region. The conditioned visual reflexes do 

 not pass across the cortex to associalfoinor motor areas. The 

 corpora striata seem to have an alternative function with the 

 stimulable cortex for the control of motor coordination. Two 

 possible hypotheses concerning the path of conditioned-visual- 

 reflex arcs are thus admitted. Either the impulses pass to tEe 

 visual projection area in the occipital pole and thence to the cor- 

 pus striatum, or they pass to the visual area and directly back to 

 lower centers without traversing any long association fibers or 

 reaching a cerebral motor area. Some evidence was found that 

 the corpora striata are not necessary for the acquirement of motor 

 habits and that the habit of the simple maze may be retained 

 after the destruction of both the stimulable cortex and the cor- 

 pora striata (section VI). The data on this point are not con- 

 clusive, but seem sufficient to raise the question of whether or not 

 the neurones of the motor areas of the cerebrum really serve as 

 the final common path of learned reactions. The possibility 

 does not seem excluded by any evidence that I know of that the 

 loss of motor control in paralysis is due, not to the interruption 

 of conditioned-reflex paths, but to some disturbance in tonic 



