Howard Hughes Medical Institute (HHMI)
researchers have made the surprising discovery that people with Alzheimer's disease
retain the capability for a specific form of memory used for rote learning of skills, even as their memories of people and events are extinguished.
The scientists' discovery suggests new strategies to improve training and rehabilitative programs that may bolster the retained cognitive function of those with Alzheimer's disease as well as healthy older people.
“From this and other studies we have done, it appears that a number of brain systems are more intact in Alzheimer's than we had anticipated,” said Howard Hughes Medical Institute researcher Randy L. Buckner at Washington University in St. Louis. “The findings suggest that if we can help people use these brain systems optimally by providing the right kinds of cues or task instructions, we may be able to improve their function.”
In an article published in the June 10, 2004, issue of the journal Neuron, Buckner and Cindy Lustig, also at Washington University, compared implicit memory capabilities in young adults, healthy older adults and those in the early stages of Alzheimer's disease.
Implicit memory is called upon when trying to recall procedures like tying a shoe. Explicit memory is used remember past associations and events. Buckner said that although researchers have used behavioral studies to distinguish implicit memory from explicit memory, the neurobiology underpinning implicit memory remains a mystery.
In anatomical terms, the kind of explicit memory that is severely impaired in Alzheimer's disease depends on the condition of the medial temporal lobe, including the hippocampus, said Buckner. “The form of memory that enables us to learn a cognitive skill is less well understood, although it is thought to depend on areas of the cerebral cortex,” said Buckner.
For their study, Lustig and Buckner recruited 34 young adults, 33 healthy older adults, and 24 older adults in the early stages of Alzheimer's disease. They designed their study to compare the implicit memory capabilities of younger and older people both with and without Alzheimer's symptoms. Lustig and Buckner presented the subjects with a series of words and asked them to decide whether the words represented living or non-living objects. They also hoped that their studies would provide a clearer picture of the regions of the brain that are employed in such tasks.
“For this task, we found that all three groups showed a significant reduction with practice in the time required to decide on a word, which is the hallmark of implicit learning,” said Buckner. While the younger adults were faster in performing the tasks, all three groups showed a robust reduction in time with practice, he said.