Fig. 6.

Changes in spatial firing patterns of hippocampal neurons during test conditions. For each type of manipulation the change in the hippocampal representation is quantified by the proportions of cells that responded in one of four different ways: no change in the spatial coding, rotation of the place field corresponding to the new distal cue positions, rotation of the place field corresponding to the new local cue positions, or one of several types of new spatial representation. The predominant proportion of cells in young rats responded to double rotation and local scramble by developing new representation, whereas the vast majority of cells in aged memory-impaired rats were following distal cues in both situations. The response pattern of aged memory-intact rats was intermediate but closer to that of young than aged memory-impaired rats. When distal cues were either rotated or scrambled a substantial minority of cells in the young and memory-intact aged rats had fields that maintained a fixed position with the constant room cues, whereas practically all cells in aged memory-impaired rats had changes in their place fields. Conversely, the groups did not differ in their responses to a single cue removal.