86 Charles H. Sawyer and M. Kawakami 



and feed-back of pituitary hormones and it must have been induced by more 

 direct means. In Fig. 6, B the sleep spindles appeared within 30 sec of 

 stimulating the septum for 30 sec at 5/sec, pulse duration 0.5 milliscc; the 

 phase of hippocampal hyperactivity started within one minute. The threshold 



A. EEG AROUSAL 



, Ret. F. 500/sec ^ 



B. EEG AFTERREAGTION "^^ 



BEFORE STIM. SP 30 SEC. I MIN. 



Lc</,s»^wvtMv.l'Kf.VfW\v/,^^^^^^^^^^^^ 4MWM'''4<'V'<«W^^^^ kmmfm>:iiMV:mii<ikitmz i 



SP v,y^H^v,^wjfAw^fMw«^'^ {i<MM^f^WMi¥fi\i' w«ww4'^t*Wtff^i^>'*yw^ l 



MM v-w«vJMH-4<*V\UH'M;Wi4*i'M'J*i» ^t^l'^\^'f>*rt^tMi^'M'^^fi'>^W^A-\''* \ViMJJK'f^MlW^*f,'flW^<v#|Vy,rvW^^^^^ ) 

 RET j^uvv(,*»aW.Wavv,Vm*^M\''*>Wv\'*a^'''^ k'/*^Vi'>V'^%M7'*>vMW/AllH'M'* 'illW(frt•'1^'^VW«♦^'^«»«^*■W*^^^^^^^^ 1 



IOO>iV 

 I SEC 



Fig. 6. EEG records of arousal (A) and afterreactions (B). Abbreviations: cf. Fig. 3. 



Explanation in text. 



is defined as the lowest voltage which will induce a complete EEG after- 

 reaction within 30 min of a single 30-sec period of 5/sec stimulation. If a 

 positive response occurs in considerably less than 30 min it is considered 

 appropriate to test a lower voltage without waiting for the full half-hour to 

 elapse. 



A completely different phenomenon is the EEG arousal response (Fig. 6, 

 A). Here a short, five-second burst of high frequency (300/sec) stimulation 

 applied to the midbrain reticular formation or related areas will, if above 

 threshold, cause a desynchronization of the frontal cortex EEG pattern and 

 a theta synchrony in the limbic cortex. If far above threshold, the response 

 will outlast the stimulus, and behavioral arousal may occur: the rabbit may 

 sit up or stand and look alert. 



The "alert" theta rhythm of the limbic cortex, hippocampus and other 

 areas is of lower frequency (4-6/sec) than the afterreaction phase of hippo- 

 campal hyperactivity (7-9/sec). During the latter phase the rabbit is so 



