In the paper review “Navigating with grid and place cells in cluttered environments” I asked a follow up question about spatial processing vs spatial memory in the HC/EC complex. The answer that was relayed back sounded like we had a crossed message regarding the essential point that these are two separate aspects. There is no question that on some spatial tasks that involve spatial memory the HC/EC is vital; damage to the EC/HC disturbs tasks that involve forming a spatial memory. When the task is structured to tease out spatial processing separately from spatial memory it seems that the EC/HC is NOT required to do spatial processing.
You have to be very careful to look at what the task is testing.
Please see this paper. This quote sums up a key finding: “The findings suggest that the hippocampus is not needed to carry out the spatial computations needed for map reading and navigating from maps.”
I recall many other papers and videos where patients with EC/HC damage are walking (in labs, inside houses, and outdoors) and had no problems in normal navigation and object manipulation as long as the task did not require memorizing the details of navigation or spatial processing.
These considerations suggest that it is very important to separate spatial processing vs spatial memory in discussing grid cells in the EC/HC. I place spatial processing outside of the EC/HC and the formation of spatial memory in the EC/HC. I do not exclude the possibility that grid cells outside the EC/HC do spatial processing.
In recent work (such as what was covered in the COSYNE review session) there does seem to be grid activity outside the EC/HC and this could be where spatial processing is happening, but the episodic spatial memory forming portion seems to be centered in the EC/HC complex.