<正>Objective: To clarify the firing characteristics of the hippocampal pyramidal cells and in-terneurons in the auditory discrimination cognition. Methods: Thirteen guinea pigs were studied by the paired （active cognition group. n=10） or unpaired （passive cognition group. n = 3） training with 1 kHz （CS+）and 500 Hz tones （CS- ） and the air puff （US） applied 250 ms after the CS+ onset. Results: In active group. 32 pyramidal cells showed exciting response to the CS+ tone. 16 cells inhibited response and 4 cells revealed no response to the high frequency tone and 18 interneurons almost unchanged. In passive group

the pyramidal cells responded to the tone casually and 10 out of the 13 interneurons remained invariably. Conclusion: The result suggests that the pyramidal cells play a major role in coding auditory information by the networks

and the interneuons may modulate it via forward and feedback.