1402 HANDBOOK OF PH^•S!OLOr;^• ^ NEl'RGPHVSIOLOf; V II 



SINGLE SHOCK 

 Q « CS.SJ 



lO/SEC STIM 



3 — 



2 _-_^. 



3 — — - 



Time intervals 

 from a f f 2 5 sec 

 f and g continuous. 



H 0.5 sec. 



I 



2 

 3 



^^-^ 



jU 



FIG. 4. Hippocampal responses to amygdaloid stimulation in the cat showing clear recruitment 

 and potentiation, a to g/ Bipolar records taken with a horizontal row of four electrodes inserted in 

 a frontal plane into the portion of the hippocampus where it overlies the pulvinar thalami. Chumii-I 

 I : Record from electrodes i and 2 located in the pulvinar where it is covered by the hippocampus. 

 Channel 2: Record firom electrodes 2 and 3, with electrode 2 in the pulvinar and 3 in the hippocam- 

 pus. Channel 3: Record from electrodes 3 and 4 located in the hippocampus. No responses from the 

 pulvinar. Gradual build-up of a high-\oltage response in the hippocampus in response to 10 cps 

 repetitive amygdaloid stimulation. The amplitude of the single-shock response, which is barely 

 visible at this gain, is increased more than 10 times at the end of the period of repetitive stimula- 

 tion. On resumption of i cps single-shock stimulation the response shows clear potentiation. The 

 insets A to D in the upper left show sequences of the same phenomena recorded with a microelectrode. 

 The tip of the microelectrode lies in the pyramidal layer of the hippocampus. Both tracings are 

 from the same microelectrode, the upper one taken with a long time constant, the lower one at a higher 

 gain with an ultrashort time constant. A: Single-shock response; small positive response, no unit 

 spikes. B: Atter 2.8 sec. of 12 cps amygdaloid stimulation, showing augmentation of the amplitude 

 of the positive response ('recruitment'), still no unit spike discharge. C: 11 sec. later during 12 cps 

 repetitive amygdaloid stimulation; pyramidal cell recruited into firing as evidenced by unit spike 

 discharging on top of a negative deflection which has developed in the trough of the initial positive 

 response. D: Second posttetanic potentiated response; unit fired as in C. Calibration for a to g, 

 5000 fiv; for .'1 to D, 250 mv. Time scale in A to D, 10 msec. [Modified from Gloor (97, loi).] 



In ihe hippocampus the different aspects of these 

 excitatory processes were most consistent with each 

 other (fig. 4); prominent, slow and gradual recruit- 

 ment was followed by marked potentiation and this 

 was often associated with a decrease in latency. In 

 other parts of the amygdaloid projection system, how- 

 ever, these different excitatory changes were often 



dissociated; for instance, in ihc ventromedial hypo- 

 thalamic nucleus where recruitment was aliscni or 

 minimal, potentiation was very prominent; again, in 

 the upper brain stem and in the piriform cortex, re- 

 cruitment was often associated with a seemingly para- 

 doxical increase of the response latency. 



Some of the discrete neuronal mechanisms under- 



