2 5 



On the Instability of a Cortical Point* 

 By T. Graham Brown and C. S. Sherrington, F.R.S. 

 (Received March 16,— Read May 2, 1912.) 

 (From the Physiology Laboratory of the University of Liverpool.) 



CONTENTS. 



PAGE 



L Introduction 250 



II. Methods Employed 251 



III. Changes in the Eesponse of a Cortical Point in Eesult of Serial 



Stimulation of it 253 



IV. Change in the Eesponse of a Cortical Point subsequent to Stimula- 



tion of a Cortical Point Antagonistic to it 260 



V. Influence of Certain Afferent Nerves upon the Eeaction of the 



Cortical Point 266 



VI. Effect of Concurrent Stimulation of Two Cortical Points Antago- 

 nistic to each other 271 



VII. Post-Central Convolution 273 



VIII. After-discharge subsequent to the Eesponse of a Cortical Point ... 274 



a. Tonic After-discharge 274 



b. Epileptoid After-discharge 274 



c. Bebounds 275 



IX. Conclusions 276 



I. Introduction. 



Slight and transient differences in the depth of narcosis, in the freedom of 

 blood supply, and in the temperature of the preparation modify reactions 

 obtained from stimulation of the motor area in the cortex cerebri with 

 a facility and to a degree not met in the study of purely spinal or 

 decerebrate reflexes. 



The observer, when first attempting to decipher the rules exhibited by the 

 reflex activities of a spinal or of a decerebrate preparation, naturally turns 

 first^to those results which lend themselves best, by regularity and harmony, 

 to exact formulation. Occasional exceptions as they arise are reserved for 

 examination in the future. In a similar manner, the codification of those 

 responses which are obtained with the greatest reliability from the several 

 cortical points is what at first cbiefly concerns the observer in the study of 

 the elicitation of different movements from different points in the cortex 

 cerebri. 



In the present observations, however, our aim has been rather to note to 

 * The expenses of this research have been in part defrayed by a grant from the 

 Carnegie Trust. 



