Scientists clarify nature of memory difficulties encountered in dementia
An international team of scientists has discovered that incomplete memories rather than memory loss is responsible for triggering mental confusion in patients with dementia.
Presented in the journal Science, the study sheds new light on how the brain's ability to maintain complete, detailed memories is disrupted, potentially knocking down theories that forgetting past events or items is what causes memory problems. The remaining and sketchier memories confuse patients, raising their chances of falsely remembering information they never encountered, according to the scientists.
Led by the University of Cambridge in the UK, the researchers used an animal model of amnesia that is widely used to determine memory impairment. Past studies on memory found that amnesic animals failed to distinguish between new and old objects. But those studies failed to show whether the animal was unable to differentiate between the objects because it saw the old object as being new (it forget something that had happened) or because it determined that the new object was old (false memory).
In this latest study, subjects were exposed to a study object, followed by a test phase in which the study object was again presented, along with a perceptually distinct new object. The subjects had to make a distinction between the new and repeated objects. This allowed the researchers to assess responses to the new and old objects separately. Animals looked at an object, and then were given a memory test an hour later that involved either the same object or a new object. Animals with no problems spent more time exploring the new object, indicating that they remembered the old object.
Meanwhile, the amnesic animals showed poor test results. They spent the same amount of time exploring new and old objects. The researchers also found that these animals spent less time exploring the new object compared to their 'normal' counterparts. The amnesic animals had false memories for the new object.
The team assessed whether performance on the memory task could be improved if there we no other memories to confuse the brain. The animals were placed in a dark, quiet space before being tested. The researchers found that amnesic animals that showed no recollection when they spent the time before the test in normal, busy conditions, showed perfect memory when they spent the time before the test in a dark, quiet environment.
'This study suggests that a major component of memory problems may actually be confusion between memories, rather than loss of memories per se,' says Dr Lisa Saksida from the Department of Experimental Psychology at the University of Cambridge, a co-author of the study. 'This is consistent with reports of memory distortions in dementia - for example, patients may not switch off the cooker, or may fail to take their medication, not because they have forgotten that they should do these things, but because they think they have already done so,' she adds.
'One thing that we found very surprising about our results was the extent of the memory recovery, achieved simply by reducing the incoming information prior to the memory test,' she points out. 'Not only does this result confound our expectations, but it also gives us a clearer understanding of the possible nature of the memory impairment underlying amnesia and certain types of dementia, which is critical to developing more sophisticated and effective treatments.'
The scientists believe their findings could lead to new treatments able to ease the confusion between memories, including drugs that enhance the complex, detailed representations needed to separate memories.
'Even more exciting would be the ability to develop treatments that could stop the disease in the early stages, rather than treatments that address the symptoms once dementia has set in,' Dr Saksida says. 'Early detection of memory impairment is critical for the development of such treatments, and a better understanding of the nature of the impairment, as we have found here, is critical to such early detection.'
Researchers from the Wellcome Trust Behavioural and Clinical Neuroscience Institute, the University of California, San Diego, US, and the University of Guelph, Canada contributed to the study.
Data Source Provider: Science; University of Cambridge
Document Reference: McTighe, S.M., et al. (2010) Paradoxical false memory for objects after brain damage. Science 330: 1408-1410. DOI: 10.1126/science.1194780.
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