Using place cells to test memory

Place cells are neurons in the hippocampus that fire when the animal occupies a specific location within its environment.   As different place cells have different place fields (locations where they fire), they are thought to provide a cognitive map for the rat. 

One approach that we've taken is to use place fields as an indicator of the animal's recognition of a previously seen environment.

Place fields in an environment become rapidly anchored to the landmarks within that environment. If you shift these landmarks (when the animal is outside the environment), the locations of the place fields will also shift.

The rapid association between where individual place cells fire and the landmarks in an enviroment provide the opportunity to test the animal's recognition of an enviroment. If the animal recognises an environment, its place cells should fire in the same location as they had in previous encounters with that enviroment.

place cells show memory

Our results show that, after an initial exposure of 10 min, rats recognise an environment after a delay of 3 h, but less so after 6 h and 24 h. Longer initial explosure (3 x 10 min) leads to longer lasting memory. Surprisingly, this memory by place cells in CA1 does not appear to depend on synaptic plasticity in the dorsal presubiculum.