1696 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY III 



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FIG. 7. F.lectrocorticogram recorded in the Rolandic region 

 in man. Note the beta rhythm 125 per sec.) from the precentral 

 areas. On command to move fingers, the resting rhythm dis- 

 appears in the hand area, but not elsewhere. It reappears when 

 movement stops. [From Jasper & Penfield (59).] 



could <i -.(ream of willed impulses be initiated, ca- 

 pable of producing the action that is appropriate to 

 all previously received information" ((14) 



Two experimental findings, drawn from the study 

 of the electrical activity of the cortex, have been put 

 forward in support of the hypothesis of a subcortical 

 origin of voluntary commands. The first is the identi- 

 fication of a type of electrical activity, specific to the 

 precentral regions, which appears in the electro- 

 corticogram as a regular rapid rhythm of 25 per sec. 

 and an intensity of 100 to 250 mv. It can, under 

 fa\ enable conditions, be detected even in the encepha- 

 logram where it often takes the form of an arch- 

 shaped rhythm of 12 to \-\ cps which Gastaut (40) 

 identified as a 'dcdoublee' form of the basic beta 

 rhythm. Such rhythmic activity, as well as the Other 

 forms of alpha activity, is generally associated with 

 a state of relative functional rest in an awake subject 



Furthermore, jusl .is the alpha rhythm of the 

 occipital areas, lor example, appears blocked by 

 visual stimulation and indicates a state of functional 

 'activation' of the perceptual system, a blocking of 

 the rolandic beta rhythm appears when a voluntary. 

 movement is being initiated and persists during its 

 execution. Jasper & Penfield (59) emphasize the 



localizing value of ibis blocking on the precentral 

 areas. A movemenl of the fingers, lor instance, 

 blocks the rhythm of the precentral regions relative 

 in the hand while allowing the rhythmic activity of 

 the neighboring regions to continue (sec tig 71. These 

 1. 11 1 have been confirmed b\ others, in particular by 

 Ga mhi 1 1 1. 111 in 1 el. 1 1 mi 1 10 a re 1 1 -shaped rhythms. 

 Penfield & Jasper emphasize another particulai 

 aspect oi this phenomenon; the blocking of the 

 rhythm seems in be associated directly, with the 



kinetic component of the intentional movement. It 

 occurs, for instance, if we ask the subject to execute a 

 scries of movements such as displacing the thumb 

 successively with the different fingers. In contrast, the 

 active maintenance of a posture is marked by the 

 rapid reappearance of the basal activity I ,g 



Penfield & Jasper accordingly suggested that the 

 impulses responsible for this abolition of the resting 

 rhythm max have a subcortical origin. As a matter of 

 fact, the evidence now accumulated by neurophysi- 

 ologists confirms the role of the subcortical centrence- 

 phalic systems in the regulation of rhythmic electrical 

 activity of the cortex (63, 95). The origin of the 

 afferents responsible for blocking and its time relation- 

 ship with the beginning of the movement remain 

 however to be made more precise. 



A second group of experimental facts concerns 

 another group of correlations recently established 

 between motor behavior and electroencephalographic 

 data. The existence of a significant relation between 

 the vei v first signs of muscular activity and the phase 

 of the alpha rhythm of the rolandic regions, during 

 the initiation of a voluntary movement, conies from 

 the experiments independently carried out by Bore- 

 ham ti al. (14) and by Bates (8). Lansing (64), 

 studying the reaction time, found it 10 be shortest 

 when the stimulus and the response both fall in the 

 same phase of the alpha rhythm recorded from the 

 occipital and rolandic areas. [See also Lindsley (77).] 



The interpretation of these data remains difficult. 

 However, it permits us to envisage a relationship 

 between the mechanisms of origination of voluntary 

 movemenl and those which control the cortical 

 rhythms. 



The earlier hypotheses of Bartlev ei Bishop (7) 

 concerning the existence of a relation between the 

 cortical alpha rhythm and the fluctuations of the 

 excitability of the cortical neurons, as well as the 

 observations of Adrian c< Morruzzi 121 on pyramidal 

 discharges attending the slow waves recorded at the 



surf. ice of the cortex, may locate the seal ol this 

 interaction at the cortical level. On the other hand, 

 the role ol the subcortical structures located in the 

 centrencephalic areas of Penfield in the control of 

 the basic rhythms of conical activity could also 

 jusiiiv the hypothesis that the interaction is Int. mil at 

 the supposedly subclinical source of the messages 

 which evoke voluntary movements. 



It would lie unjustified to overemphasize the value 

 ul such experimental evidence the interpretation ol 

 which still remains quite hypothetical. In anv event, 

 I'enlield's verv interesting views on the centrence- 



