XL: When you zoom in into the hippocampus, of course you will see lots of cells, but we are able to find which cells are involved in a particular memory, because whenever a cell is active, like when it's forming a memory, it will also leave a footprint that will later allow us to know these cells are recently active.
刘旭：当你聚焦于海马体， 当然你会看到许多脑细胞， 但我们也能够找到参与 某一特定记忆的那些细胞， 因为每当一个脑细胞在活动时， 比如说当它正在形成一段记忆时， 它也会同时留下“足迹”，通过这些足迹我们可以得知 这些脑细胞近期有活跃过。