Check out the answer by Ajit Rajasekharan.
Very nice answer:
https://www.quora.com/What-are-the-major-differences-between-grid-cells-and-place-cells-and-why-do-we-need-them-both
What does this have to say to SDR and HTM?
First - think of the hippocampus as a sort of encoder for time and space. Patient HM shows that this is not the space where long-term memory is stored but we can’t form these without the hippocampus. Grid/place/boundary/path/head direction are all things that are parsed out and somehow passed to the cortex. Once in the cortex, it is usable “as is” so the cortex must duplicate this spatial map in some way.
Speculation: The vestibular “self” is not mentioned anywhere in this but it absolutely must be part of time and space calculations. The codes are envirocentric. There must be personal space in there somewhere. The tissue between must be the part that relates you in the environment.