Abstract: Changes in cortical and hippocampus electro-activity during learning were studiedon the rabbit. The results are as follows: 1. The hippocampus shows slow rhythm theta waves and the cortex shows desyn-chronization during formation of conditioned reflex. 2. In the formation of conditioned reflex cortical and hippocampus activities arerelated in that cortical changes are always linked with hippocampus changes, but hip-pocampus changes are not necessarily accompanied by cortical changes. Furthermore,hippocampus changes are much more obvious. 3. During the process of the formation of conditioned reflex, formation rate onthe third and fourth day is the highest, then it gradually decreases. 4. Strongly established conditioned reflexes are easily differentiated and moredifficult to extinguish.

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