ABSTRACT
Behavior is used to assess memory and cognitive deficits in animals like Fmr1-null mice that model Fragile-X Syndrome, but behavior is a proxy for unknown neural events that define cognitive variables like recollection. We identified an electrophysiological signature of recollection in mouse dorsal CA1 hippocampus. During a shocked-place avoidance task, slow-gamma (SG: 30-60 Hz) dominates medium-gamma (MG: 60-90 Hz) oscillations 2-3 seconds before successful avoidance, but not failures. Wild-type but not Fmr1-null mice adapt to relocating the shock; concurrently, SG/MG maxima (SGdominance) decrease in wild-type but not in cognitively inflexible Fmr1-null mice. During SGdominance events, place cell ensembles represent distant locations; during place avoidance, these are avoided places. During shock relocation, wild-type ensembles represent distant locations near the currently-correct shock zone but Fmr1-null ensembles represent the formerly-correct zone. These findings indicate that recollection occurs when CA1 slow gamma dominates medium gamma, and that accurate recollection of inappropriate memories explains Fmr1-null cognitive inflexibility.