The amnesias

Throughout history, memory and amnesia have been central to philosophical thought and empirical investigation. There has been particular interest in whether there are multiple forms of memory, how they are represented in the brain, how they are parsed following neurological compromise, and how their breakdown is best characterized. Differential abilities among amnestic individuals have advanced the distinction between various forms of memory, such as implicit and explicit memory in the case of H.M., and episodic and semantic memory in the case of K.C. This overview brings together a variety of perspectives on memory and the amnesias, from Clinical Neuropsychology, Neurology, and Cognitive Science, to Animal and Human Neuroscience. We begin with a brief history of the study of memory organization in the healthy brain and dissociations in memory as uncovered in extensively studied cases of amnesia. Memory impairment resulting from damage to the medial temporal lobe (MTL), diencephalon, basal forebrain, and the frontal lobes is then elaborated, with a focus on MTL amnesia, which has received the most attention among memory researchers. Alternative theories of MTL amnesia are considered through a selective review of the current amnesia and neuroimaging literatures on the seemingly disparate roles of the hippocampus in episodic and spatial memory, future imagining, perception, implicit memory, and working memory. If amnesia is a disorder that is not restricted to explicit (consciously accessible) memory, this will force us to rethink the way in which memory is represented in the human brain. WIREs Cogn Sci 2012, 3:47-63. doi: 10.1002/wcs.155 For further resources related to this article, please visit the WIREs website.