W. R. ADEY 581 



behaviour was kittenish, and they were sexually immature. At this time 

 they showed a great deal of 4 cycles/sec. activity in 'resting' records. 

 During the approach performance they showed typical 5-6 cycles/sec. 

 activity in the ventral hippocampus and in the entorhinal area, but there 

 was much less of it in the dorsal hippocampus than in the adult animal. It 

 appeared characteristic of the immature animal that there was a much 

 wider distribution of the 'specific' 5-6 cycles/sec. activity in the approach 

 performance and that it included the ventral hippocampus. In contrast to 

 adult animals, these bursts appeared dissociated in moment of onset in 

 different hippocampal leads, and in duration m different leads. 



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Fig. 3 

 .Simultaneous EEG and tinic-lapsc photographs of animal's approach in T-box. The dividing 

 partition appears at the top of each frame. During the approach to the incorrect side (frames 

 2-5) there is a burst of 6 cycles/sec. activity in the entorhinal lead (ENT). This disappears as the 

 animal stands, turning head from side to side (frames 6-10) and reappears as the animal 

 changes position to the correct side of the box (frames 11 and 12). The amygdaloid record 

 (AMYG) shows 40/scc. activity typical of the hungry animal, which disappears momentarily 

 on attainment of the food reward. 



In such immature animals, trained to a high level of performance over a 

 period of 60-90 days, it was observed that much of the random hippo- 

 campal slow activity disappeared, and that the behaviour became much 

 like an adult cat. Very strikingly, 6 cycles/sec. activity now appeared in 

 the dorsal hippocampus during the approach performance, as seen typi- 

 cally in the adult animal. 



With Dr Holmes, we have also trained adult cats in a delayed response 

 situation, in which a 7 second delay preceded approach to a concealed 

 food reward. During the waiting period there was much 4 cycles/sec. 



