SEPTOHIPPOCAMPAL SYSTEM AND THE PRELIMBIC SECTOR OF FRONTAL-CORTEX - A NEUROPSYCHOLOGICAL BATTERY ANALYSIS IN THE RAT

Rats with lesions in the posterodorsal septal area (aimed at transecting the precommissural fornix) and rats with lesions in the prelimbic sector of the medial frontal cortex were tested postoperatively on a neuropsychological test battery comprised of the following tasks: time-spent-eating in two adaptation boxes, time-to-emerge and ambulation in an open field, general activity, contingently-reinforced (continuous) and schedule-specific (delayed non-matching-to-sample) T-maze alternation, visual and olfactory discrimination in a T-maze, temporal alternation (response patterning) and tactile Go/No-Go discrimination in a runway, approach-avoidance conflict in the runway, step-through inhibitory avoidance, one-way active avoidance, two-way active avoidance, and conditioned taste aversion. It was found that: (1) rats with septal (SEP) lesions spent more time eating than control (CON) rats and rats with lesions in prelimbic cortex (PRE). PRE rats did not differ from CON rats; (2) PRE rats emerged into an open field faster, and spent less time in home cage than CON and SEP rats. SEP rats stayed in home cage less than CON rats. PRE and SEP rats crossed more squares in the open field than CON rats; (3) SEP and PRE rats were more active than CON rats; (4) SEP rats performed the contingently-reinforced and schedule-specific T-maze alternation tasks worse than PRE rats, and PRE rats performed these tasks worse than CON rats. PRE, but not SEP, rats showed improvement with continued practice at brief intertrial and interrun intervals. However, the performance of PRE rats deteriorated at longer intervals and did not reach CON levels even with continued practice; (5) CON, SEP and PRE rats performed a visual discrimination task in the T-maze equally well. However, SEP rats performed an olfactory discrimination task in the same maze better than CON and PRE rats; (6) SEP, as opposed to CON and PRE, rats were not able to pattern their responses in a straight runway; (7) SEP and CON, but not PRE, rats were able to master a tactile Go/No-Go discrimination task in the runway; (8) SEP and PRE rats took a higher number of shocks than CON rats in an approach-avoidance conflict test, but there were no group differences in total running latency; (9) CON, SEP and PRE rats did not differ in the performance of the step-through inhibitory-avoidance task; (10) CON and SEP rats had a higher number of avoidance responses than PRE rats in the one-way active-avoidance task; (11) SEP rats performed the first session of the two-way active-avoidance task better than CON and PRE rats; (12) PRE rats drank less water than CON and SEP rats, and SEP rats drank less saline than CON and PRE rats; (13) CON, but not SEP and PRE, rats were able to learn a conditioned taste aversion task; (14) intraperitoneal injections of physostigmine did not ameliorate the low performance of SEP rats in the schedule-specific T-maze alternation task 4 months after the first postoperative test. The results can be considered consistent with the hypothesis that the septohippocampal system and the prelimbic sector of the medial frontal cortex are important for working/representational memory mechanisms. However, our study indicates that there seems to be a hierarchy such that the septohippocampal system plays a larger role than the prelimbic cortex. Additionally, our data suggest that the prelimbic cortex is involved in the shifting of cognitive strategies. © 1990.