322 HANDBOOK OF PHYSIOLOGY ^ NEUROPHYSIOLOGY I 





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FIG. 8. SP change accompanying barbiturate spindles in a 

 pentobarbitalized cat. / and 2 indicate ECG and SP records, 

 respectively. .-1. Spontaneous barbiturate spindles with tran- 

 sients which are chiefly negative accompanied by a negative 

 shift in SP which outlasts the spindle. B. Same cat shortly after 

 the application of veratrine (io~0 'o cortical surface. The 

 transients in the spindles are now chiefly positive and the SP 

 change accompanying the spindle has also become positive. 

 [From Goldring & O'Leary (13).] 



applied before veratrine the barbiturate spindles 

 may at first show an accentuation of their negative 

 components accompanied by nes;ati\e after-effect; 

 when veratrine takes effect the principal polarity of 

 the spindle changes from negative to positise and the 

 after-effect also comes to have a positive polarity. 



SP Concomitants of Convtilsoid Discharge 



These have been studied in detail in the rabbit 

 (11, 12). Such a cortical discharge can be initiated 

 locally by surface-positive polarization across the 

 cortex, by repetitive stimulation (10 to 16 per sec.) 

 in the related thalamic relay nucleus, or by strychnine 

 applied locally in sufficient concentration. In animals 

 stimulated repeatedly and vigorously such paroxysms 

 may commence to appear intermittently without 

 preceding activation. The latter situation is analogous 

 to the abrupt appearance of con\ulsi\e discharge in 

 man. 



With few exceptions the course of SP change during 

 convulsoid activity has been a positive shift of i.o to 

 1.5 mv correlated with the build-up of the discharge 

 in the ECG tracing. As the tonic discharge becomes 

 clonic the SP commences to return toward the pre- 

 paroxysmal balance; as the discharge ceases SP con- 

 tinues to shift negatively, sometimes reaching a value 

 of 5 mv negative to the preparoxysmal balance (fig. 

 9). When paroxysms follow each other in quick suc- 

 cession, a positive SP shift occurs with each, and a 

 negative one coincides with the intenseizure silent 

 period. 



The initiation of a paroxysm by polarization 

 applied acro.ss the cortex from surface to white matter 

 has particular interest in view of the polarization 



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FIG. 9. Steady potential change during paroxysm in rabbit. 

 Light ether anesthesia. Paro.xysm induced by repetitive 10 per 

 sec. stimulation of the lateral geniculate nucleus with bipolar 

 electrodes. Straight white line of each trace indicates the base 

 line of the ampliher from which the d.c. change is a departure. 

 Record from optic cortex with transcortical leading, positive 

 up. .'1. Start of stimulation of lateral geniculate nucleus indi- 

 cated by an evoked response following each stimulus. No con- 

 sistent change in SP was observed during this period. B. 1 2 sec. 

 after start of stimulation. In this strip the positive phase of 

 evoked response has dropped out and the later negative com- 

 ponent of evoked response has commenced to double, indicating 

 the start of the paro.xysm which persists into the poststimulatory 

 period. Vertical white lines indicate end of period of stimula- 

 tion. As paroxysm commences SP commences to shift positively. 

 C. 15 sec. after start of stimulation. SP has continued to shift 

 positively. D. 20 sec. after the start of stimulation. Further 

 positive shift as the poststimulatory paroxysm reaches its maxi- 

 mum. E. 25 sec. after start of stimulation. Paroxysm diminishing 

 in intensity and SP is now commencing to shift negatively. F 

 and G. 35 and 40 sec. after start of stimulation. The paroxysm 

 disappears as SP shifts further negatively. 



theory advanced by Libet & Gerard (30) and 

 supported by Bishop & O'Leary (2). Such applied 

 polarization ma\' be expected to shift the charges 

 along the pyramidal neurons, perhaps increasing or 



