Alzheimer’s and a shrinking hippocampus

Research published in Alzheimer’s Research & Therapy investigates the association between memory performance and the size of the hippocampus, a part of the brain essential for forming new memories. Co-author of the work reveals more about their findings here.

Alzheimer’s disease is a progressive neurological disorder that results in changes in memory, language, personality, and ability to live independently, among other skills. Currently, more than 5 million individuals in the U.S. are diagnosed with Alzheimer’s disease, and this number is expected to rise as the population ages.

Alzheimer’s disease results in progressive loss of tissue throughout the brain. In particular, an area of the brain called the hippocampus tends to show the most rapid loss of tissue earliest in the disease course.

The hippocampus is essential for forming new memories, such as what one ate for lunch or a recent conversation. The progressive shrinkage of the hippocampus is responsible for the short-term memory loss that is the hallmark symptom of Alzheimer’s.

Hippocampal volumes and memory performance

Although there is currently no effective treatment for the disease, there is increasing interest in identifying the disease at its earliest stages, as early intervention may be most effective in combatting it.

Given their increased risk of developing dementia, individuals with MCI have been studied extensively and can shed light on processes that may occur prior to disease onset.

Identification of assessment techniques for use in clinical trials of Alzheimer’s therapies is, therefore, essential. Use of disease markers, such as hippocampal volumes and memory performance, is also useful in diagnosis and treatment planning.

Mild Cognitive Impairment (MCI) represents a pre-dementia state, in which an individual shows changes in memory or other thinking skills but continues to function fairly normally in daily life. Given their increased risk of developing dementia, individuals with MCI have been studied extensively and can shed light on processes that may occur prior to disease onset.

In our study, we examined the relationship between the size of the hippocampus and measures of both verbal memory (such as learning and recalling a list of words) and non-verbal memory (such as learning and recalling geometric shapes) in a large sample of patients in our memory clinic, including a group of individuals diagnosed with MCI. Our goal was to determine whether the memory measures were closely related to the size of the hippocampus.

What did we find?

Overall, we found strong relationships between the memory measures and hippocampal volumes in the sample as a whole, suggesting that these measures may serve as effective indicators of hippocampal size. In particular, performance on the measure of non-verbal memory was most closely related to hippocampal size among the larger sample.

When we looked at the sample of individuals with MCI, a similar pattern emerged. Specifically, the non-verbal memory task showed much stronger associations with hippocampal volumes than a comparable verbal memory task.

The reasons for this remains unclear, although it is possible that requirements of the non-verbal task itself make it a more rigorous measure of hippocampal integrity. Further research is required to examine this question.

It is noteworthy that most clinical trials of Alzheimer’s disease treatments have used only verbal measures in assessment of memory. Our findings suggest that inclusion of non-verbal memory measures will be an important consideration for future trials, as well as clinical assessment of patients being evaluated for memory loss.

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