Spatial- and locomotion-related neural representation in rat hippocampus following long-term survival from ischemia.

Spatial and locomotion-related behavioral correlates of hippocampal cell discharge were compared between ischemic and sham-control rats performing a spatial maze. Ischemic rats showed impaired choice accuracy during maze acquisition, but not during asymptote performance. Single-unit correlates during asymptote performance revealed enhanced spatial selectivity of CA2/3 complex-spike cells coincident with attenuated place-specific firing by hilar complex-spike or subicular cells. Responsivity to locomotion state by stratum granulosum interneurons was exaggerated, and locomotion-induced changes in firing of hilar and subicular interneurons was reduced. Ischemic rats showed recovered spatial learning abilities as evidenced by the fact that acquisition of the spatial task in a second environment was not impaired. Because representational reorganization was also observed in ischemic, maze-naive rats, brain injury per se appears to change information coding schemes.