A STUDY OF SOME TWENTIETH CENTURY 

 THOUGHTS ON INHIBITION IN THE SPINAL CORD 



David P. C. Lloyd 



The Rockefeller Institute, New York 



In presenting the following account of thoughts on the subject of central 

 inhibition my purpose is not to make a foray into medical history, for which 

 others are so much better fitted than am I, but to reflect, in so far as I am 

 able, the status of thought on inhibitory mechanism at the present time, and 

 the background from which it has arisen. This necessitates a survey of ideas 

 and their origins, unfashionable as well as fashionable. I would begin with a 

 discussion of the background, then of the overall situation as it stood 20 

 years ago when direct inhibition as a central action was demonstrated beyond 

 any doubt. Finally, I would touch upon some specific topics of current 

 interest. 



It is well to have before us a definition of our subject, and I know of none 

 better than that of Gasser (1937) which serves admirably in, to use his own 

 words, "the absence of an exact definition". Inhibition, then 



"is a term of convenience used without exact definition in connection with a group of 

 phenomena having certain quahties in common. The essential condition is the stoppage 

 or prevention of action through the temporary operation of a process which does not 

 harm the tissue. It is usually also implied that the process results from nervous activity, 

 or imitates the result of nervous activity." 



THE BACKGROUND 



At the beginning of this century inhibition as a central action was firmly 

 established. Setschenow (1863) had shown that crystals of salt placed on the 

 frog brain stem delayed the time of onset of Tiirks reflex, and Sherrington 

 had, in his series of papers on reciprocal innervation, left no room for doubt 

 as to the existence of central inhibition and of its role in the genesis of 

 reciprocal action. Attempts had been made to account for inhibition. One 

 finds in these the beginnings of a dichotomy that has played a large role in 

 thought on the mechanism of inhibition and which cannot even today be 

 resolved completely. The sources of this dichotomy lie, on the one hand, in 

 the experiments of the brothers Weber and Weber (1845) on vagal inhibition 

 of the heart in which eff'ect was clearly an action, and, on the other hand, in 



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