5 : 5/ Electrical Potentials of the Brain 101 



five minutes per set, a total of about four hours is necessary. By making 

 judicious choices, this time can be reduced to an hour, but a great many 

 paper recordings must be closely scrutinized. 



On analyzing these records, four types of abnormalities associated with 

 brain tumors are found. These are: a S-rhythm; a 0-rhythm; high 

 voltage single spikes or multiple spikes at 10-20 cps; and episodic or 

 continuously enhanced a-rhythms. None of these abnormal rhythms 

 are due to tumor tissue which is always silent, but the abnormalities are 

 most pronounced in the part of the brain nearest the tumor. The eeg 

 changes are most useful in localizing abnormal growths along the surface 

 of the cerebral cortex, but there are no major changes in the eeg pattern 



E.E.G. Patterns 



Normal 



Eyes Open 

 Nonspecific Dysrhythmia 



Spike and Wave 



Multiple Spike and Wave 

 Slow Spike 



Delta 



I sec 



Figure 7. The various abnormal eeg patterns each have specific 

 clinical implications. For example, the "spike and wave" is 

 characteristic of petit mal seizures. Original figure of R. G. 

 Bickford, M.D., Mayo Clinic. 



on the scalp because of tumors along the brain stem. Bilateral 

 differences in the eeg patterns also help locate cerebral tumors. 



Another clinical use of eeg patterns is for studies of epilepsy. In 

 general terms, an epileptic seizure is an uncontrolled hyperexcitability 

 and spontaneous discharge of part of the central nervous system. If the 

 discharge occurs in motor areas of the cerebral cortex, the person has a 



