MESSES. F. GOTCH AND V. HORSLEY 



EXCITATION OF CORTEX. 



1. Electrical Changes Observed in the Spinal Cord. 



The arrangement expressed in the above headings is the fundamental experiment 

 designed to elucidate, if possible, the nature of the impulses which pass from the 

 cortex to gain and traverse the bulbo-spinal centres. The desirability of avoiding 

 shock, which so markedly lowers the excitability of the cortex, led us to choose to 

 investigate the electrical effects which accompany the impulses as they pass through 

 the mid dorsal region, so that the section of the cord was made in the Cat imme 

 diately below this point, and in the Monkey, just above or through the uppermost 

 part of the lumbar enlargement. (See figs. 4 and 5.) 



This selection of the seat of section had the additional advantage that it enabled 

 us to proceed at once to the determination of further points, viz., the localisation of 

 the upper and lower limb areas in the cortex, and thus to generally control the results 

 obtained, as will be shown presently. We will first describe a typical experiment. 



The anaesthetised animal having been arranged as described (Chapter III.) the dura 

 mater was exposed over the so-called motor area of the lower limb ; the spinal cord 

 was then exposed at the level of about the 7th dorsal vertebra, raised in air and 

 connected to the non-polarisable electrodes. The character of the resting electrical 

 difference between the cut end of the cord and the uninjured surfaces of the columns 

 was noted as set forth in Chapter IV. 



(a) Effects seen in the Electrometer. 



The electrodes were, in the first instance, connected with the capillary electro 

 meter. 



The dura mater was then opened, and the surface of the cortex excited (vide p. 299). 

 The effects observed in the electrometer were 



(1.) A persistent negative variation of the difference lasting as long as the excitation 

 was applied to the cortex. 



(2.) A series of intermittent negative variations commencing (sometimes after a 

 short interval had elapsed) from the cessation of the excitation, and continuing for a 

 variable period according to the state of the cortex. 



We may with advantage at once briefly review the general questions raised by 

 this result, as such a discussion will make clearer the object of further researches. 



The effect seen in the electrometer was so identical in character with that obtained 

 from the muscles in an epileptiform convulsion started by similar excitation of the 

 cortex as to suggest that the essential features of the muscular convulsion are 

 wholly due to the character of the cortical discharge. This is illustrated by the 



