Figure 6.

Place field responses of aged memory-impaired rats to arena rotations over repeated sessions. For explanations, see Figure 5. Sessions are abbreviated S1–S8. Illustrations for sessions 7 and 8 contain two cells to show remapping within the novel environment. A, Aged memory-impaired rat R5 recorded for eight sessions. The spatial representations did not rotate with the arena rotation in sessions 1, 2, 4, and 6, but, in sessions 3 and 5, they did rotate. Sessions 2–4 are illustrated with the same cell, whereas for all other sessions, different cells are shown. Note that even the same cell in sessions 2–4 responded differently on different days. In session 7, the place fields rotated but remapped (new location or disappeared) in trial New3 instead of returning to their original positions. In session 8, the place fields were replaced by a new one in trial New2R that rotated in trial New3 with the arena frame. Note that cell 1 (the same cell in both sessions 7 and 8) appears to have two different place fields, reflecting a kind of multi-stability. B, Aged memory-impaired rat R8 recorded for eight sessions. In sessions 1, 3, and 4, the spatial representations did not rotate with the arena, whereas they followed the arena rotation in sessions 2, 5, and 6. Sessions 1–6 all are illustrated by the same cell, again showing that individual cells sometimes rotated and sometimes did not. Another two cells are used to illustrate both sessions 7 and 8. Note that, in sessions 7 and 8, the two cells appear to each have two representations of the same environment without regard to the landmarks. This is strongly suggestive of multi-stability.