A first kiss, an exotic vacation, a sports team championship, a child's first words: all are memorable events. But when someone has amnesia, have the memories been completely purged from the brain or are they simply irretrievable? Is amnesia a defect in memory storage, or memory recovery?
This has been a vexed question for more than 30 years. Most psychologists tended to support the retrieval-deficit explanation, while neuroscientists interested in how memories work at a molecular and cellular level backed the idea of storage-failure.
This disconnect has limited both scientific and clinically relevant advances. But in a collection of articles published today by the journal Learning & Memory, leaders in the field of memory studies have thoughtfully reconsidered the enigma of amnesia, as well as the methodological and conceptual problems in its study. They point out how studies of amnesia have been important in forming our current understanding of how memory works, and they propose novel ways of experimentally evaluating the neurobiological basis of memory impairment. The resulting section, entitled "The Neurobiology of Amnesia," includes eight articles, all of which are available online today at http://www.learnmem.org.
"Questions about the nature of amnesia are ultimately biological questions," explains Dr. Larry Squire, Professor of Psychiatry at the University of California, San Diego, and one of the contributors to the special section. "But some of the best-known and most-often-cited evidence is founded on a behavioral-psychological level of analysis. What we really need to be asking is: 'In amnesia, what actually happens to the synaptic changes that carry the memory?'"
"There is evidence that bears on that question," says Dr. Squire. In an experimental setting, animals can "recover" from amnesia under a variety of conditions, something that should be impossible if the memory was not initially stored. But the major challenge is to experimentally assess whether an animal has truly recovered a memory or simply re-learned a task.
Because amnesia is rarely complete and there is often some residual performance ability, it can be argued by supporters of the storage-failure theory that any "recovery" from amnesia reflects new learning added onto the residual memory. The retrieval-failure theory cannot easily be attacked because one can argue that a memory remains inaccessible until the appropriate retrieval cues are provided.
Dr. Karim Nader, Professor of Psychology at McGill University (Canada), is the guest editor of the Learning & Memory special amnesia section. "This compilation of articles brings many of the perspectives concerning the nature of amnesia side-by-side for consideration," he says. "We hope that it will inspire readers to think of new ways to bridge the different positions and levels of analyses, and that it will give new momentum to the search for answers to the fundamental nature of amnesia."
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