Introduction During the last decade increasing numbers of clinical reports have appeared linking memory deficits in man with bilateral lesions of the rhinencephalic structures. The careful psychological studies of Scoville and Milner1 and Penfield and Milner2 have provided strong documentation that supports the clinical impressions of other writers. Particularly striking has been the demonstration that other cognitive functions are unimpaired even in the face of severe deficits in memory. Encouraged by the apparent consistency and specificity of the association between memory defects and rhinencephalic lesions in man, a number of investigators have attempted to produce similar disturbances of memory in primates and lower mammals. The testing situations have attempted to reproduce the three types of memory defects reported in the human studies: retrograde memory loss, or loss of retention of a habit; impairment of acquisition, or inability to learn; and short-term or recent memory loss. While loss of