Comparison of perirhinal cortex ablation and crossed unilateral lesions ofthe medial forebrain bundle from the inferior temporal cortex in the rhesus monkey: Effects on learning and retrieval

Seven monkeys learned new object-reward associations and scene problems and were overtrained on 100 problems of each type. Four monkeys received cross ed lesions of the medial forebrain bundle (MFB) and inferior temporal corte x, with the later addition of a fornix section ipsilateral to the MFB lesio n. The remaining 3 monkeys received bilateral perirhinal cortex ablation. D isconnection of the MFB from the inferior temporal cortex impaired postoper ative new learning, but the retrieval of problems overtrained preoperativel y was relatively preserved. Subjects with perirhinal cortex ablation were s everely impaired in new learning and at the retrieval of scene problems, bu t retention of object-reward associations was relatively well preserved. Th e results support the hypothesis that isolation of the inferior temporal co rtex from basal forebrain and midbrain afferents results in dense anterogra de amnesia, whereas the role of the perirhinal cortex in learning is depend ent on the perceptual difficulty of the task.