198 



Information Storage and Neural Control 



■,'<f " 



Pre. 



Tet. 



3cps 



[c d 



Fig. 8. Influence of tetanization across a cortical section. Cat is unanesthetized, 

 awake, and carries implanted bipolar electrodes arranged so that recording (R) 

 and stimulating (S) pairs are within an island of neuronally isolated cortical 

 tissue while the tetanizing (T) pair is on the intact cortex outside the isolated 

 zone. Pre- and post-tetanization voltage is the same as that used in the tracing 

 labeled "3 cps." Stimulating voltage is then reduced 50% (A) and 70% (B). 

 The pre-tetanization voltage is then resumed and then stimulation stopped (D). 

 Further explanation in text. Calibration: 100 microvolts and 100 milliseconds. 

 (Chow, K. L. and Dewson, J.: unpublished data.) 



a longer latency and a hump on the descending limb. The response 

 had never occurred prior to tetanization and was clearly locked 

 to the stimulus frequency. However, in the waking animal (Fig. 7B) 

 where spontaneous background rhythms were more prominent, 

 phase locking was much less precise and it was difficult to be sure 

 of a response truly related to the stimulus frequency. 



In order to determine whether the effect of tetanization on the 

 responsiveness of cells at the recording site was mediated through 

 synaptic connections rather than by an electrotonic or field effect, 

 a neuronally isolated cortical slab was prepared. The blood supply 

 to the slab was preserved. The electrodes were arranged so that 

 the stimulating and recording pairs were within the isolated zone 

 but the tetanizing pair was placed outside (Fig. 8). 



