A peculiar pattern of temporal involvement of rat perirhinal cortex in memory processing

By means of the fully reversible tetrodotoxin inactivation technique, perir hinal cortex (PC) mnemonic function was investigated in rats trained to a p assive avoidance response (PAR). It was shown that PC functional integrity is necessary during PAR acquisition, during late and very late consolidatio n (from 24 hr up to 192 hr after the training session), and during retrieva l. An unexpected finding was that the PC was not involved in the early cons olidation period. Thus the PC may play a relatively simple relay or connect ive role during acquisition, but its very late and very long consolidative involvement may indicate a peculiar function in consolidation and possibly in the storage of the PAR engram. The results are discussed in terms of the mnemonic characteristics of other neural sites (amygdala, hippocampus, and entorhinal cortex) involved in the same learning process.