Their own review paper "Place cells, grid cells, and the brain's spatial representation system." gives a good overview of their research directions i believe. I

Their own review paper "Place cells, grid cells, and the brain's spatial representation system." gives a good overview of their research directions i believe. It can get pretty technical though, and it's behind a paywall: http://www.ncbi.nlm.nih.gov/pubmed/18284371 http://www.ncbi.nlm.nih.gov/pubmed/18284371