"The 'similar' response was the critical response for us, because it let us know that participants could distinguish between similar items and knew that they're not identical to the ones they'd seen before," Yassa said. "We found that older adults tended to have fewer 'similar' responses and more 'old' responses instead, indicating that they could not distinguish between similar items."
Yassa said that this inability among older adults to recognize information as "similar" to something they had seen recently is linked to what is known as the "perforant pathway," which directs input from the rest of the brain into the hippocampus. The more degraded the pathway, the less likely the hippocampus is to store similar memories as distinct from old memories.
"We are now closer to understanding some of the mechanisms that underlie memory loss with increasing age," Yassa said. "These results have possible practical ramifications in the treatment of Alzheimer's disease, because the hippocampus is one of the places that deteriorate very early in the course of that disease."
The team's next step would be to conduct clinical trials in early Alzheimer's disease patients using the mechanisms that they have isolated as a way to measure the efficacy of therapeutic medications.
"Basically, we will now be able to investigate the effect of a drug on hippocampal function and pathway integrity," he said. "If the drug slows down pathway degradation and hippocampal dysfunction, it's possible that it could delay the onset of Alzheimer's by five to 10 years, which may be enough for a large proportion of older adults to not get the disease at all. This would be a huge breakthrough in the field."
|Contact: Lisa De Nike|
Johns Hopkins University