Neurotoxic damage to the hippocampal formation impairs performance on the transverse patterning task (Alvarado et al., 1998, SFN ABST #366.4). However, recent data indicate that surrounding medial temporal cortical areas also play important roles in object memory, suggesting that they may be critical for performance of this task. Thus, we tested monkeys with aspiration lesions of either the perirhinal cortex (PRh) or parahippocampal areas TH/TF (TH/TF), and normal controls on two sets of transverse patterning problems. The animals were trained in 3 successive phases as follows: Phase 1, A+ B-, Phase 2, A+ B-, B+ C-, Phase 3, A+ B-, B+ C-, C+ A-. Note that only in Phase 3 is a configural/relational solution required for accurate performance. Trials to criterion for Phases 1, 2 and 3 respectively were: Controls: 31.7, 75.0, 522.5. TH/TF: 35.0, 85, 923.0. PRh: 33.3, 83.0, 925.0. Both experimental groups differed from Controls in Phase 3 (p's < 0.05) but not in Phases 1 and 2. Only one monkey in Group TH/TF co...