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HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY I 



Bates (7) reported a tendency for the \oluntary move- 

 ments of human sulsjects to be synchronized in phase 

 with their alpha rhythms, and this effect has been 

 observed in several ways. The experiments of Lansing 

 (37) indicate that the shortest and longest visuomotor 

 reaction times in some human subjects tend to fall at 

 points about 50 msec, apart in opposite phases of the 

 alpha cycle. There was also some relation between 

 motor response and spontaneous tremor, a fact sug- 

 gesting that cyclic changes in excitability were operat- 

 ing also at the level of the spinal motoneuron pool. 

 This is perhaps to be expected since the control of 

 voluntary movement is not belie\ed to depend upon 

 complex activation of reflex circuits through high 

 central structures. Obser\ations of these relations 

 have so far yielded only statistical information; there 

 is no clear indication of how the timing and gating 

 mechanism operates, and there are many exceptions 

 to any rule that can be formulated. Experiments with 

 auditory rather than visual stimuli have given even 

 less conclusive results (44). In planning and inter- 

 preting such experiments it is important to allow for 

 the tendency of some intrinsic rhythms to be pulled in 

 to synchrony by the signals which they or other 

 rhythms may in turn control. This interaction, to- 

 gether with integration b\- receptors, may be responsi- 

 ble for the discrepancies in the reports by different 

 observers. 



EJfect of Temperature Changes 



The ease with which alpha frequency can be meas- 

 ured and its constancy in normal conditions has en- 

 couraged the study of the effects of metabolic change. 

 Hoagland (28) induced fever artificially and reported 

 a rise in alpha frequency with temperature of nearly 

 0.5 cycles per sec. per degree C in normal subjects 

 and an even higher temperature coefficient in 

 syphilitic patients. Krakau (36), using an optical 

 method of frequency analysis, was unable to confirm 

 this effect in all his subjects and suggested that what- 

 ever changes may occur during artificial fever might 

 be due to the general arousal by the situation as much 

 as to the rise in temperature. This seems likely, since 

 measurement of alpha frequency in a few subjects 

 with the toposcope has shown no regular variation of 

 alpha frequency with the normal diurnal changes of 

 body temperature which would be expected to result 

 in fluctuations of about 0.25 cycles per sec. It would 

 seem that the alpha mechanisms are to some extent 

 protected from the primary efTects of temperature 

 change. 



DELT.'K, THETA AND BETA RHYTHMS 



Relation of Delta and Tlieta Rhythms to Age 



As a representative of the class of intrinsic rhythms, 

 alpha activity is unique in its close and clear relation 

 to sensory function. The other forms of rhythmic ac- 

 tivity in the human brain, designated by Greek 

 letters for convenience rather than clarity, are more 

 familiar in clinical than in physiological studies, but, 

 apart from the paroxysmal discharges associated 

 uniquely with epilepsy, all are found in normal condi- 

 tions. Delta and thcta rhythms are characteristic of 

 infancy and childhood, accompanying the maturation 

 of normal children in a highly variable but significant 

 manner (60). They precede, but in later years are 

 often mingled with, adult alpha rhythms and their 

 rate of subsidence is a common measure of develop- 

 ment. 



Delta Rhythms 



When delta rhythms persist appreciably beyond 

 the age of 10 or 12, the character of the child 

 is usually suggestive of immaturity in a particular 

 fashion to which Hodge et al. (29) have given 

 the name ductility, the tendency to be led easily. In 

 the extreme this is associated with minor recidivist 

 delinquency combined with an appealing personality. 

 In such cases the delta rhythms are often most prom- 

 inent in the right teinporo-occipital region and show 

 little responsiveness to stimulation. Another type of 

 delta rhythm is seen in some children with immature 

 but not necessarily defective personalities. This is bi- 

 lateral, monorhythmic and strikingly responsi\e to 

 stimulation, acting almost as an alpha rhythm, par- 

 ticularly when it is localized to the occipital lobes. In 

 otherwise normal people there is no obvious explana- 

 tion of this effect, but a similarly responsive rhythmic 

 slow activity is seen also in patients with organic dis- 

 turbance of deep midline structures, and it is pos- 

 sible, therefore, that this type of slow responsive 

 rhvthm is an expression of inadequacy of the diffuse 

 arousal systems. Corroboration of this can sometimes 

 be obtained from suppression of the delta rhythms by 

 administration of activating drugs, such as ampheta- 

 mine, which are believed to act on the diffuse ascend- 

 ing reticular formation. 



The association of delta activity with disease, 

 dystrophy, damage and deep sleep — from which 

 alliteration the phenomenon was accorded its designa- 

 tion — has suggested that it may have some sort of 

 limiting or protective function (54, -,6\ This notion 



