In an article in the June 10, 2004, issue of Neuron, Cindy Lustig and Randy Buckner reported evidence that older people with symptoms of early-stage Alzheimer's still showed capabilities of "implicit memory" similar to young adults and older adults without symptoms.
Implicit memory -- one type of which is developed by repetition or "priming"-- is a type of memory required to perform tasks. It is distinct from the explicit memory for events and people that is profoundly affected by Alzheimer's. To some extent, even healthy older adults with no Alzheimer's symptoms complain of loss of explicit memory. Each type of memory seems to draw on different regions of the brain, researchers have found.
In their experiments, Lustig and Buckner asked 34 young adults, 33 older adults without any Alzheimer's symptoms, and 24 older adults showing memory loss and other symptoms of early-stage Alzheimer's to perform a classification test on words visually presented to them on a screen. The subjects were asked to classify the words as representing either living or nonliving subjects. Although the younger adults outperformed the older and Alzheimer's groups, all three showed a marked reduction in the time to do the classification with practice -- a characteristic of priming.
The researchers next performed functional magnetic resonance imaging on the brains of all three groups as they performed the classification task on a mix of old and new words.
The researchers found that the brain area associated with such tasks -- the left prefrontal area of the cerebral cortex -- showed repetition-related reductions in activity as all of the subjects repeated the tasks. Such activity reductions are characteristic of learning with practice, in which the brain area reduces its activity as it adapts to a task. The researchers also found that this reduction in brain activity correlated with the reduction in the response time as subjects learned the task.
"Taken together, these findings may have implications for designing environmental modifications and training programs to maintain and improve the performance of older adults and possibly other clinical populations," wrote the authors.
Cindy Lustig, and Randy L. Buckner: "Preserved Neural Correlates of Priming in Old Age and Dementia"
Published in Neuron, Volume 42, Number 5, 10 June 2004.