Conducted 3 experiments in which septal lesions in 14 male Long-Evans hooded rats produced a performance deficit on a task involving the integration of isolated sensory experiences. Neither cingulate nor midline thalamic lesions (N = 7 Ss) had a comparable effect. The deficit in performance by Ss with septal lesions could not be accounted for in terms of an increase in perseverative tendencies. Preoperative experience, although not facilitating reasoning performance in septal Ss, did affect the kinds of errors on the task. 2 possible bases for the observed reasoning deficit are suggested: a failure to attend to relevant stimulus aspects resulting from heightened exploratory tendencies or a loss of recent memory. (30 ref.) (PsycINFO Database Record (c) 2006 APA, all rights reserved)