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 conditioned taste aversion was assessed using two different conditioning methods, 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 aversion, was also assessed. Electrolytic lesions of insular cortex blocked behavioral expression of a conditioned taste aversion and this was evident not only when lesions were placed prior to conditioning, but also when they were made after conditioning but before testing. In contrast to the effects on behavior, lesions did not completely block the c-Fos-immunoreactivity which accompanies re-exposure to the aversive taste. In addition, the blocking of behavioral evidence of aversion conditioning by cortical lesions was seen both in animals trained under an intraoral acquisition procedure and those trained with bottle-conditioning. This contrasts with previous work with amygdala lesions which showed that amygdala was absolutely necessary for taste aversions conditioned with the intraoral method but not for those conditioned using bottle presentation of the taste. Overall, these findings imply that the details of the neural circuitry involved in taste aversion learning, including its anatomical distribution, complexity and degree of redundancy, vary with the type of conditioning method employed.