Consolidation of a socially acquired olfactory memory involves interactions among a network of cortical and hippocampal regions

The observation of temporally-graded retrograde amnesia following hippocampal damage suggests that the hippocampus plays a critical, time-limited role in memory consolidation. However, these studies do not indicate where permanent memory is stored, nor do they clarify whether the hippocampus normally remains involved in a non-essential way. Recent evidence from multiple neural imaging studies indicates the time-limited role of the hippocampus and suggests that cortical regions are the final repository of long-term memory. However, each of these previous studies used spatially based tasks. Three experiments assessed hippocampal and olfactory cortical involvement during consolidation of the non-spatial, hippocampal dependent social transmission of food preference task (STFP).; The effect of cholinergic depletion of the orbitofrontal cortex (OFC) on the STFP task was assessed. Injection of the cholinergic neurotoxin 192 IgG-saporin into the OFC resulted in a significant decrease in the percentage of trained food eaten compared to sham operated control rats. This finding reveals the critical involvement of the OFC in the acquisition of STFP suggesting a role in the retrieval of the task.; Anatomical patterns of activation of the immediate early gene c- fos during retrieval of STFP memory immediately, one-day, two-days, and 21 days after training were assessed. Hippocampal areas were activated during retrieval shortly after learning but the level of activation declined at successive times. In contrast, a network of olfactory recipient regions including piriform, entorhinal, and orbitofrontal cortex showed low activation in the initial retrieval tests and greater activation at successively later times. These findings show that the piriform, entorhinal, and orbitofrontal cortex are critical sites for the long-term storage of a non-spatial memory.; Orbitofrontal and piriform cortical activation was assessed using c- fos during STFP retrieval after radiofrequency lesions of the hippocampus. Hippocampal lesions 1 day, but not 21 days, after training impaired retrieval of STFP at 30 days. Increased activation was seen in the piriform cortex in both hippocampal damaged groups regardless of performance. The increased activation seen in the piriform cortex but not the OFC suggests that the piriform cortex may be especially critical for the long-term storage of an olfactory based non-spatial memory.