CHAPTER XIII 



Changes associated with forebrain 

 excitation processes: d.c. potentials 

 of the cerebral cortex' 



JAMES L. O'LEARY 

 SIDNEY GOLDRING 



Divisions of Neurology and Neurosurgery, and the Beaumont May Institute of 

 Neurology, Washington University School of Medicine, St. Louis, Missouri 



CHAPTER CONTENTS 



Suggested Technique for Cortical D.C. Recording 

 Experimental .Studies 



Spontaneous SP Changes Correlated with Interruption in 

 Usual Resting Cortical Rhythm 



After-effects of Evoked Responses 



SP Changes Associated with Recruiting Responses 



SP After-effects of Strychnine and Veratrine .Spikes 



SP Concomitants of Convulsoid Discharges 



D.C. Changes Which Accompany Spreading Depression (SD) 



Relation of Polarity of Evoked Transient to Polarity of SP 

 Change Also Consequent to Stimulation 



Effects of Stimulation at a Distance Along a Multisynaptic 

 Path Upon Transcortical SP 



Injury Potential Components 



Human Studies Using Scalp Recording 

 Discussion of Origin of Steady Potentials 

 Summary 



BESIDES THE SPONTANEOUS and evoked potentials con- 

 ventionally recorded from the cerebral cortex, the 

 exposed brain in a resting state ordinarily shows a 

 voltage difference between cortical surface and ven- 

 tricle (d.c. potential). If the brain is not disturbed 

 following its preparation for recording, this pia- 

 ventricular potential may remain relativeh' steady, 

 and for that reason we have referred to it as steady 

 potential (SP). 



' .'Mded by grants from the .Allen P. and Josephine B. Green 

 Foundation and the Public Health Service (B-882). 



The role SP plays in neuronal functioning can be 

 assayed only after taking account of the nonneuronai 

 sources which complicate its interpretation. It is also 

 necessary to differentiate such d.c. potentials from 

 those of pH and oxygen electrode recording. The 

 latter, although employing a d.c. method, depend 

 upon the change which occurs in a critical electrode 

 as a result of a tissue change in its milieu. By contrast, 

 the d.c. recording described hereafter employs very 

 stable electrodes to register changes in the distribution 

 of electrical charge in the intervening tissue. 



Reduced oxygen tension incident to systemic de- 

 terioration, or intracellular poisoning of respiratory 

 enzyme systems (e.g. by cyanide ions) can produce 

 predictable changes in it. Injury effects and anesthesia 

 are unavoidable complications of any experimental 

 neurophysiological procedure and can also result in 

 SP alterations. Cbntrol of these and possibly other 

 factors which limit the applicability of the method is 

 necessary if we are to reach an understanding of the 

 relation between spontaneous and evoked potentials 

 of the usual electrocorticogram and SP changes 

 which may develop coincidentally or subsequently. 



Several early studies of d.c. potential are relevant 

 to the approach outlined here. Libet & Gerard (30) 

 first showed that a pia-\entricular potential exists in 

 the frog brain, postulating that a change in such 

 potential can alter spontaneous cortical activity. 

 Jasper & Erickson (22) at about the same time ob- 

 served a d.c. voltage component associated with high 



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