The effects of septal lesions on discrimination
Four cats received bilateral electrolytic lesions of the septum and were tested postoperatively for retention of a simple discrimination task (Phase I) and acquisition of a successive discrimination task (Phase II) in comparison to seven normal control animals. A daily session during Phase I consisted of 50 trials; each with a 10 second reinforcement period indicated by a 7 cps flashing light, (SD period) during which the animals had to learn to bar press for a milk reinforcer and a 30 second variable intertrial interval during which the animal had to learn to inhibit the bar pressing response. The performance measures included: 1) number of sessions to criterion, 2) number of SD responses, and 3) number of intertrial responses. Following criterion performance of Phase I, Phase II was begun. The animals received 60 daily trials during Phase II, one half of which were the same as during Phase I , (SD trials) and the other half of which were indicated by a 3 cps flashing light (S trials). Reinforcement was withheld during an S trial and the animals had to inhibit bar pressing during this period. The following measures were obtained: 1) number of sessions to criterion, 2) number of responses during SD trials, 3) number of responses during S trials, and 4) number of intertrial responses. The findings of the experiment included: 1) inconclusively, no deficit in postoperative performance measures in comparison to preoperative levels during Phase I, and 2) no differences between performance measures of septal and control animals during Phase II. Inhibitory functions of the septum were not supported. Two explanations were suggested for the lack of collaboration with the inhibitory role of the septum. First, the lesions of the septum sustained by the animals were small and rather precisely confined to the septum. Some of the fornix was destroyed but the damage was slight. The second explanation pointed to identical stimulation and response requirement during both phases of the experiment. A bar pressing response during the presence of a 7 cps flashing light was required in both situations, and may have improved the performance of the successive discrimination during Phase II.