INTRINSIC RHYTHMS OF THE BRAIN 



297 



has been called by \^'alter the phylactic hypothesis. 

 Since the brain is poorly endowed with certain of 

 the protective devices conducive to the preservation 

 of other organs — such as pain and repair — it is reason- 

 able to conjecture that some mechanism may exist to 

 constrain or restrict the influence of conditions likely 

 to initiate excessive and persistent actixity. The rela- 

 tively great size and wide extent of delta rhythms — 

 which may reach potential differences of i mv on 

 the scalp — suggest that as electrotonic inhibitors they 

 may in times of distress give the brain a chance to 

 survive through inactivation of its cells. 



Theta Rhythms 



The class of theta rhythms — which were at first con- 

 fused with slow alpha rhythms and later identified as 

 related to thalamic lesions (62) — is most character- 

 istically associated in normal young people with feel- 

 ings of disappointment and frustration. They are 

 evoked most easily by the termination or withdrawal 

 of an authentic agreeable stimulus and often show a 

 markedly stereotyped pattern of growth and decline 

 over a period of about 20 sec. or so following such an 

 experience. Clinically their persistence is linked with 

 psychopathic character traits. It has been suggested 

 (55) that, if the alpha rhythms be considered as scan- 

 ning for visual pattern, then theta rhythms may rep- 

 resent a scanning for visceral pleasure. Such an 

 analogy of analogies is notoriously meretricious, but 

 if comprehension is to grow, some working hypothesis 

 must be formulated, and at least experiments can be 

 planned to discover why, just as the alpha rhythms 

 wax great at the moment when patterns are excluded 

 by closing the eyes, so theta rhythms tend to arise at 

 the conclusion of pleasure. 



Beta Rhythms 



The beta rhythms, which were the second class of 

 brain activity to be identified by Berger, are still un- 

 certain in their significance and even in their defini- 

 tion. Mundy-Castle (43) has proposed that beta 

 rhythms be considered in two classes, beta I and beta 

 II. Beta I is suppressed during cortical activity and is 

 often, though not invariably, harmonically related to a 

 component of the alpha rhythms; this relationship is 



responsible for the wave form of the rythme en arceau of 

 Gastaut (22). In order to avoid further confusion in 

 this already disordered domain, it might be conven- 

 ient to designate his particular combination of rhythms 

 the ■ ^' rhythm because of its resemblance to the outline 

 of the Greek letter. The beta II of Mundy-Castle is aug- 

 mented during cortical activity and may represent 

 an acceleration or concentration of efferent activity 

 arising from the .scansion of cortical regions engaged 

 in the analysis of endogenous or exogenous patterns. 

 Precise classification of these rhythms — which are 

 particularly elusive because of their rate and the 

 restriction of their domains — must await further study 

 of their location and functional correlates. 



ORIGIN OF INTRINSIC RHYTHMS 



The various intrinsic, apparently spontaneous, yet 

 often responsive, electrical rhythms of the brain are 

 clearly in a different class of phenomenon from the 

 unitary propagated spike potentials which act as the 

 main operational code elements in the nervous system. 

 The slower rhythmic oscillations seem more likely to 

 be involved, as it were, in the administrative depart- 

 ments of central neurophysiology. If their rate of dis- 

 charge were less constant or their wave form less pure, 

 they might be considered as trivial projections of 

 spatially asymmetric postsynaptic potentials in large 

 populations of pyramidal cells with particularly long 

 dendritic proces.ses. It is indeed conceivable that the 

 degree of asymmetry and the electric moment of the 

 dendritic potentials might be large enough in some 

 circumstances to generate the fields observed on the 

 scalp. Even if this is the mechanism of generation, 

 however, the gross variations from person to person 

 and the delicate relations between the frequencies, 

 time relations and geometric properties of the rhythms 

 with the character and actions of the organism suggest 

 that the intrinsic rhythms are more than the resultant 

 of adventitious topography. The processes of evolu- 

 tion are too parsimonious to allow such entities to be 

 multiplied beyond necessity. The refineinents of 

 modern techniques should enable schools of investi- 

 gators trained in complementary disciplines to solve 

 this enigma which so impedes our understanding of 

 brain function. 



REFERENCES 



1. Adrian, E. D. and B. H. C. Matthews. Brain57: 355, 1934. 



2. Adrian, E. D. and K. Yamagiwa. Brain 58: 323, 1935. 



3. Arvanitaki, a. Arch, internal, pkjsiol. 52; 381, 1942. 



4. ."^SHBY, VV. R. Design for a Brain. London: Chapman, 1952. 



