142 K. S. LASHLEY 



vided for inducing functional changes in nerve conduction wfiich 

 may have a direct bearing upon the hypotheses mentioned above. 

 It may serve, at least, to distinguish the first, the " inhibition 

 theory," from the others, since, if this theory be true, the reduc- 

 tion of inhibitory processes should retard learning, while the 

 resultant increase in the ease of spread of excitatory processes 

 might be expected to accelerate learning, either by increasing 

 the variety of activities available for selection by repetition 

 (third hypothesis), or by increasing the effects of reinforcing 

 agents such as are presupposed by the second hypothesis. Thus, 

 if strychnine retards learning, it should lend some support to 

 the first hypothesis, if it accelerates it, it will give evidence in 

 favor of the second or third. 



The interpretation of the results may be complicated, how- 

 ever, by the locus of attack of the drug. Experimental work 

 has located this definitely only in the intercommunicating cells 

 of the dorsal horn of the spinal cord, but the involvement 

 of the entire body in the convulsions of acute strychnine poison- 

 ing indicates a similar reduction of inhibitory processes in the 

 midbrain, or perhaps even in the cerebrum. The reduction 

 of stimulus threshold found by Amantea ('15) after application 

 of strychnine to restricted parts of the cortex also shows an in- 

 creased excitability of the cortex and probably closely similar 

 action of the drug upon cortical and spinal cells. This evidence 

 seems sufficient to justify the interpretation of any effects of 

 the drug found as due to its general reduction of synaptic re- 

 sistances. 



It was with essentially the above problem in mind that I 

 began a study of the effects of strychnine upon habit-formation. 

 Since caffeine is generally stated to have a physiological action 

 similar to that of strychnine but confined to the cerebrum and 

 since it is so generally used as a stimulant it was included with 

 strychnine in this study of the effects of the central excitants. 



The three hypotheses outlined above, while most widely 

 accepted, by no means exhaust the possible explanations of 

 the learning process and the results reported in the following 

 pages have, perhaps, complicated rather than simplified the 



