Insular cortex lesions and taste aversion learning: effects of conditioning method and timing of lesion

The specific role of insular cortex in acquisition and expression of a cond itioned taste aversion was assessed using two different conditioning method s, which vary mode of taste delivery. Involvement of insular cortex in the induction of c-Fos-immunoreactivity in the nucleus of the solitary tract, a cellular correlate of the behavioral expression of a conditioned taste ave rsion, was also assessed. Electrolytic lesions of insular cortex blocked be havioral expression of a conditioned taste aversion and this was evident no t only when lesions were placed prior to conditioning, but also when they w ere made after conditioning but before testing. In contrast to the effects on behavior, lesions did not completely block the c-Fos-immunoreactivity wh ich accompanies re-exposure to the aversive taste. In addition, the blockin g of behavioral evidence of aversion conditioning by cortical lesions was s een both in animals trained under an intraoral acquisition procedure and th ose trained with bottle-conditioning. This contrasts with previous work wit h amygdala lesions which showed that amygdala was absolutely necessary for taste aversions conditioned with the intraoral method but not for those con ditioned using bottle presentation of the taste. Overall, these findings im ply that the details of the neural circuitry involved in taste aversion lea rning, including its anatomical distribution, complexity and degree of redu ndancy, vary with the type of conditioning method employed. (C) 1999 Elsevi er Science B.V. All rights reserved.