Discussion of hsw28's comment: Paper left quite a few unanswered questions that perhaps could have been addressed without too much extra work: 1) I would have liked to have seen results for treadmill running without train movement, as there were some differences in results between "free running" and treadmill-on-train running (for example, firing fields undergo random remapping between forward travel and free running but NOT between forward and backward travel) so a direct comparison would have been useful. 2) Similarly, I would have liked to have seen all the results for backwards travel when the animal was just being moved by the train but not running on the treadmill. In Supp fig 5, there are theta phase results for this situation, but no results for composition of place fields, head direction cells, etc. 3) It would have been interesting to see if theta phase or place cell fields during backwards movement shifted with familiarity with the track, and/or with exposure to external room cues that could be maintained during both backwards and forwards travel. It would also be cool (since it's an area of interest to me) to see what replay looks like after backwards travel, but that is a bit outside the scope of this paper.