102 Electrical Potentials of the Brain /5 : 6 



violent seizure with muscular spasms followed by unconsciousness. This 

 is called a grand mal seizure. In other persons, the sensory areas of the 

 cortex are hyperexcited, producing sensory illusions such as buzzing in 

 the ear, spots of light, or nausea, followed by unconsciousness. Illusions 

 followed by unconsciousness are called petit mal seizures. Another type 

 of epileptic seizure is called psychomotor, an attack in which the person 

 has sensory illusions followed by inappropriate automatic actions and 

 then amnesia. All three types have characteristic eeg patterns, such as 

 those shown in Figure 7. For a given patient, these eeg abnormalities 

 are more constant than the exact nature of the seizure. All are 

 characterized by large, low frequency waves. 



One might be tempted to conclude that the size of the eeg indicated 

 the degree of nervous activity. However, there are also electrically 

 silent seizures in which the normal potentials are markedly decreased. 

 The eeg is nonetheless useful in determining the type of epilepsy, choosing 

 the treatment, and following the patient's progress. 



6. Summary 



The eeg patterns are tantalizing in that they seem to be intimately 

 associated with the over-all action of the brain. They are useful for 

 clinical purposes, just as a patient's temperature may be of interest to 

 a physician with no knowledge of temperature control mechanisms on the 

 cellular level. The fundamental question of interest to the biophysicist 

 is : In what way are the eeg patterns related to the actions of the neurons 

 of the brain ? This question has not been answered. 



It may be that extending measurements to lower frequencies, small 

 regions of the brain, and so forth, may provide more clues. It seems 

 more probable that what is needed are new ideas concerning the inter- 

 pretation of the data and the planning of additional experiments. 



REFERENCES 



The form and action of the central nervous system are described in many texts. 

 The following were used in writing this chapter. 



1. Best, C. H., and N. B. Taylor, The Physiological Basis of Medical Practice, 7th 

 ed., 1 96 1 (Baltimore, Maryland: Williams & Wilkins Company). 



2. Ranson, S. W., and S. L. Clark, The Anatomy of the Nervous System: Its 

 Development and Function, 10th ed., 1959 (Philadelphia: W. B. Saunders 

 Company) . 



