Post-training lesions of the medial prefrontal cortex interfere with subsequent performance of trace eyeblink conditioning

Rabbits were trained on trace eyeblink (EB) conditioning until they reached a criterion of 10 consecutive EB conditioned responses (CRs). Electrolytic lesions were made in the medial prefrontal cortex (mPFC) centered on the prelimbic area ( Brodmann's area 32), at five different intervals after training. These included immediately, 24 h, 1 and 2 weeks, and 1 month after training. Separate groups of animals received sham lesions at these same intervals after training. After a 2 week postoperative recovery period, all animals were retested for 3 d on trace conditioning, using the same parameters used during preoperative training. Mean EB conditioning performance deficits occurred in the animals with mPFC lesions compared with sham-lesioned animals on the first day of retesting in all five groups. However, by the second or third day of retesting, the rabbits with lesions were performing at a level that was comparable with that of sham animals. Rabbits that received more posterolateral lesions of the neocortex did not, however, show postoperative conditioning deficits. A comparison of percentage EB CRs of animals with postoperative training with that of animals that received mPFC lesions before training suggests that the mPFC post-training lesions produce damage to a retrieval process and not to a storage site or an acquisition process.