Involvement of the anterior insular gustatory neocortex in taste-potentiated odor aversion learning

When an odor conditioned stimulus (CS) precedes illness (unconditioned stimulus; UCS), rats acquire relatively weak odor aversions. Conversely, when a compound odor-taste (flavor) CS precedes illness, rats acquire robust aversions both to the odor and to the taste components of a compound flavor CS. Thus, tastes potentiate odor-illness aversions during toxiphobic conditioning. Such conditioning effects have been referred to as taste-potentiated odor aversion learning (POA). Previous neurobehavioral experiments have shown that the anterior insular gustatory neocortex contributes to conditioned taste aversion (CTA) learning. The present experiment examined the involvement of the anterior insular gustatory neocortex in CTA learning and POA learning. To that end, four distinct groups of rats received bilateral electrolytic lesion placements in the orbitofrontal neocortex, the "somatic" gustatory neocortex, the anterior insular gustatory neocortex or the posterior insular neocortex. Control animals received anesthesia only. Subgroups of animals thereafter received aversion conditioning using either an odor (almond) CS or a compound odor-taste (almond-saccharin) CS. Aversions to the almond odorant and/or saccharin tastant were evaluated during extinction. Results indicated that animals lacking orbitofrontal neocortex or posterior insular neocortex acquired normal CTAs and POAs. Animals lacking somatic gustatory neocortex exhibited impaired CTA learning, yet those animals showed normal POA learning. Lesions centered in the anterior insular neocortex impaired both CTA learning and POA learning. These results demonstrate that the insular gustatory neocortex is uniquely involved in the higher-order integration of odors, tastes and illness.