Prolonged inactivation of the hippocampus reveals temporally graded retrograde amnesia for unreinforced spatial learning in rats

► We explored the role of the hippocampus during the consolidation period of spatial memory in rats. ► Rats received intrahippocampal muscimol infusions beginning 3 h or 5 days after acquisition. ► Rats in the 3-h group did not retain an object location when tested with a functional hippocampus. ► Rats in the 5-day group retained the location of an object when tested with a functional hippocampus. ► Consistent with consolidation theory, we show a gradient of memory loss for spatial information.