Involvement of the insular cortex in retention of conditioned taste aversion is not time dependent

In fear-associated learning paradigms, hippocampal lesions induce memory deficits of recent but not remote memories, while amygdala lesions produce retention deficits irrespective of the age of the memory. In conditioned taste aversion (CTA), non-hippocampal mediated learning paradigm, the insular vortex (IC) has shown to have a crucial role in consolidation and storage of CTA memory. Due to the functional and anatomical similarities to the hippocampus, a time dependent role of the IC in CTA retention cannot be ruled out. To test whether the IC shows a time dependent role in CTA memory retention, male Wistar rats were CTA trained on saccharin 0.1% (LiCl 0.15 M, 2% b/w, 40 min after drinking) and lesioned with ibotenic acid (200–300 nL, 5 mg/mL) unilaterally into the IC 1 week or bilaterally 1 or 6 weeks after CTA. CTA memory was completely disrupted in both bilateral lesion groups but unaffected in the unilateral lesioned group. The resulting preference was comparable to that of the bilaterally IC lesioned animals exposed to the taste for the first time, proving that in these animals a complete amnesic state was achieved. Bilaterally IC lesioned rats showed normal discrimination between preferred (sucrose 5%) and non-preferred (quinone) tastes. Our data indicates that the involvement of the IC in CTA is not time dependent and that CTA memories are stored in each hemisphere separately.

Research highlights
► Rats IC lesioned bilaterally either 1 or 6 weeks after CTA show amnesia.
► Preference of amnesic and IC lesioned rats exposed to taste for first time is equal.
► Amnesia is complete as bilaterally IC lesioned rats treat the taste as novel.
► Amnesic rats show normal discrimination between preferred and non-preferred tastes.
► Unilateral IC lesions performed 1 week after CTA induce no retention deficits.