Unilateral amygdala inactivation after training attenuates memory for reduced reward.

This experiment examined the effects of unilateral inactivation of the amygdalae on memory for reduction in reward magnitude. Male Sprague-Dawley rats with bilateral cannulae in the amygdala were trained to run a straight alley for ten 45-mg food pellets. On Day 10, half the animals were shifted to a 1 pellet food reward and half continued to receive 10 pellets. After the shift, the shifted animals displayed a marked increase in response latencies. Immediately following training on Day 10, the animals received bilateral intra-amygdala infusions (0.5 microliter/side) of phosphate buffer or 2% lidocaine in one amygdala simultaneously with infusion of buffer in the other amygdala. On Day 11, the shifted animals given bilateral buffer infusions displayed an increase in response latencies greater than that of the unshifted groups or the shifted groups given lidocaine unilaterally. On Day 12, the runaway latencies of the Shifted Vehicle group remained significantly higher than those of the Unshifted Vehicle group and the Shifted Unilateral Lidocaine-Right group but were not significantly different from those of the Shifted Unilateral Lidocaine-Left group. Also, the latencies of the Shifted Unilateral Lidocaine-Left group were significantly longer than those of the Shifted Unilateral Lidocaine-Right group. These findings indicate that post-shift inactivation of only one amygdala can attenuate the response to reward reduction. These results are consistent with previous evidence that the right amygdala may be more involved than the left in consolidation of memory storage for aversive experience.