Information about which structures and connections in the brain that are important for memory has come from studies of amnesiac patients and from systematic experimental work with animals. Work in animals includes studies which assess the effects of selective brain lesions on memory, as well as studies using neurophysiological recording and stimulating techniques to investigate neural activity within particular brain regions.
An important development that has occurred in the area of memory during the past two decades was the establishment of an animal model of human amnesia in the monkey (Mahut and Moss 1984; Mishkin 1982; Squire and Zola-Morgan 1983). Prior to this and the cause of the resurgence of interest in this area, Scoville and Milner (1957) had previously described the severe amnesia that followed bilateral surgical removal of the medial temporal lobe (patient H.M.). This important case demonstrated that memory is a distinct cerebral function, dissociable from other perceptual and cognitive abilities. Before H.M., due particularly to the influence of Karl Lashley, memory functions were thought to be widely distributed in the cortex and to be integrated with intellectual and perceptual functions. The findings from H.M. established the fundamental principle that memory is a distinct cerebral function, separable from other perceptual and cognitive abilities. The implication was that the brain has to some extent separated its perceptual and intellectual functions from its capacity to lay down in memory the records that ordinarily result from engaging in perceptual and intellectual work.
To support this hypothesis, it was found that surgical lesions of the medial temporal lobe in monkeys, which were intended to approximate the damage sustained by patient H.M., reproduced many features of human memory impairment. In particular, both monkeys and humans were