CHAPTER XI 



Intrinsic rhythms of the brain 



W . GREY W ALTER ' Burden Neurological Institute, Bristol, England 



CHAPTER CONTENTS 



Generation of Spontaneous Oscillation 



Piesalence of Spontaneous Rhythms 



Origin of Spontaneous Activity 



Conditions for Oscillation 

 Simple harmonic motion 

 Relaxation oscillators 

 Distinction between simple harmonic and relaxation 



oscillators 

 Electrical equivalent of hydraulic model 

 Spontaneous Electrical Activity in Excitable Tissues 



Rhythmic Activity in Single Units 



Rhythmic Activity in Networks 



Rhythmic Activity in Primitive Organs 



Intrinsic Rhythms in the Human Brain 

 Properties of Alpha Activity as Typical of Intrinsic Rhythms 



Early Reports 



Individuality of Alpha Rhythms and I'heir Variation 



Complexity of Alpha Rhythms 



Identification of Alpha Components 



Degree of Constancy and Range of Variation in Alpha 

 Frequency 



Effects of Activation and Stimulation 



Synchronization of Alpha Rhythms 



Evidence from Intracerebral Electrodes 



Relation Between Alpha Rhythms and Effector Function 



Effect of Temperature Changes 

 Delta, Theta and Beta Rhythms 



Relation of Delta and Theta Rhythms to Age 



Delta Rhythms 



Theta Rhythms 



Beta Rhythms 

 Origin of Intrinsic Rhythms 



GENERATION OF SPONTANEOUS OSCILLATION 



Prevalence oj Spontaneous Rhythms 



DURING THE 30 YEARS that have elapsed since Berger 

 first bcffan to record electrical acti\it\- from human 



brains, many suggestions ha\e been made to account 

 for the unexpected spontaneity and regularity of these 

 rhythmic potential changes which resemble so little 

 the familiar action potentials of the peripheral nerve. 

 Rhythmic electrochemical activity is not in itself a 

 rare phenomenon; it is common in primitive or- 

 ganisms and can appear even in simple inorganic 

 chemical reactions such as that between iron and 

 nitric acid or between mercury and hydrogen perox- 

 ide (39). Such reactions, of course, involve more than a 

 simple combination of forces or reagents; for the 

 generation of rhythmic actixity there must always be 

 present in the system some sort of circular or feed-back 

 pathway through which the effect of products of 

 the reaction can influence the state of the original 

 reagents. 



Origin of Spontaneous Activity 



In such a system where action and reaction are 

 intercoupled, activity once initiated will tend to 

 persist, but the first cause may be obscure. ' Spontane- 

 ous' acti\ity is in fact a difficult conception to define 

 or illustrate in practice and the situation is not 

 simplified by substituting the terms 'endogenous', 

 'autogenous' or 'autochthonous', for in all these words 

 there is iinplicit the assumption that the behavior of 

 the system depends not on its previous state but in 

 some way on itself, as if there were an element of 

 choice or free will. This implication is verbal rather 

 than philosophical and need not be taken very seri- 

 ously; the difficulty is mainly that man-inade ma- 

 chines are designed for obedience rather than for origi- 

 nality and it is difficult to define the use of function of a 

 mechanism that seems to act independently of outside 

 influences. Clearly, if the electrical rhythins of the 

 brain were entirely spontaneous and independent 

 they would be very hard to fit into any hypothesis of 



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