Critical role of insular cortex in taste but not odour aversion memory.

Conditioned odour aversion (COA) and conditioned taste aversion (CTA) result from the association of a novel odour or a novel taste with delayed visceral illness. The insular cortex (IC) is crucial for CTA memory, and the present experiments sought to determine whether the IC is required for the formation and the retrieval of COA memory as it is for CTA. We first demonstrated that ingested odour is as effective as taste for single-trial aversion learning in rats conditioned in their home cage. COA, like CTA, tolerates long intervals between the ingested stimuli and the illness and is long-lasting. Transient inactivation of the IC during acquisition spared COA whereas it greatly impaired CTA. Similarly, blockade of protein synthesis in IC did not affect COA but prevented CTA consolidation. Moreover, IC inactivation before retrieval tests did not interfere with COA memory expression when performed either 2 days (recent memory) or 36 days after acquisition (remote memory). Similar IC inactivation impaired the retrieval of either recent or remote CTA memory. Altogether these findings indicate that the IC is not necessary for aversive odour memory whereas it is essential for acquisition, consolidation and retrieval of aversive taste memory. We propose that the chemosensory stimulations modulate IC recruitment during the formation and the retrieval of food aversive memory.