Electrolytic but not ibotenic acid lesions of the posterior cingulate cortex produce transitory facilitation of learning in mice.

The rate of acquisition of 12 Hebb-Williams mazes was studied after restricted bilateral lesions of the anterior (ANT) or posterior (POST) cingulate cortex in BALB/c mice. In a first experiment, animals with electrolytic lesions were tested with the different mazes at 3 time intervals between 19 and 48 days after surgery. The rate of acquisition in POST-lesioned mice was observed to be facilitated at the 2 first time intervals (between days 19-22 and 32-35), but this effect was reversed (impairment) when the test was carried out between 45-48 days postsurgery; no significant effects were observed in ANT-lesioned mice. In a second experiment, the same behavioral paradigm was used in mice with restricted ibotenic acid lesions of the POST cingulate cortex. These lesions had no significant effects on the acquisition of the mazes. A third experiment was carried out to test if the postoperative delay itself contributed to the long latency of the impairment observed in Expt. I. No impairment of acquisition was observed when POST cingulate lesioned animals underwent their first learning session between 45-48 days after surgery; in contrast, a significant facilitation of the performance was observed at this time. These results suggest an involvement of the posterior cingulate cortex, and in particular the cingulum bundle, both in acquisition and long-term memory processes.