The evidence that amnesia in humans is caused by lesions of the medial temporal lobes is very strong, but there is considerably less evidence that basal forebrain lesions can also cause amnesia. Although there is a large body of animal data indicating that basal forebrain structures play a part in memory, the human evidence is limited to a few case studies. One feature of the patients reported on is that although they have fairly specific brain damage, there is invariably damage to more than one structure so that strong inferences about the effects of very focal damage on memory are difficult or impossible. Most attention has been focused on the corticopetal, mainly cholinergic system, which comprises the septum, the diagonal …