Size of These Brain Parts Tied to Dementia Risk

Medically Reviewed by Hansa D. Bhargava, MD on October 15, 2015
From the WebMD Archives

Oct. 15, 2015 -- When brain structures called hippocampi are smaller, that may point to a higher risk of getting Alzheimer's disease and other types of dementia, new research suggests. People who did better on certain memory tests tended to have larger hippocampi.

These two seahorse-shaped structures deep inside the brain are important for navigation and for storing and retrieving memories. In people with dementia, the hippocampi are often the first regions of the brain to suffer damage.

Earlier studies have found a link between the volume (size) of hippocampi and the risk of dementia, but the results have been conflicting. Also, few studies have included people with mild cognitive impairment (MCI), a condition that often precedes dementia.

Size Matters

In this latest study, published in Alzheimer's Research and Therapy, researchers recruited 226 people attending memory clinics. Thirty-four participants had Alzheimer's disease, 95 had MCI, 25 had normal memory (for their age), and the remainder (72) had neurological disorders, including other types of dementia.

The average age of the participants was 68, but those with Alzheimer's disease were significantly older than the participants with normal memory.

All of the participants completed verbal and visuospatial memory tests before undergoing an MRI brain scan. Visuospatial ability relates to understanding and determining spatial relationships, such as location. In Alzheimer’s, visuospatial problems can cause a person to become disorientated in familiar places or fail to recognize familiar people. The MRI scans were used to determine the size of the hippocampi.

Spatial Memory

The link between the size of the hippocampi and a person's performance on the memory tests was stronger for the visuospatial test than for the verbal test. This suggests that visuospatial memory tests may be a better way to gauge someone's risk of dementia than verbal memory tests.

The study finding "challenges earlier studies and clinical trials which focused on verbal memory alone, as we're now finding that spatial memory is a bigger player in assessment of those at risk for Alzheimer's disease," says lead researcher Aaron Bonner-Jackson, PhD, an associate at the Cleveland Clinic Lou Ruvo Center for Brain Health.

Larger Studies Needed

"We've known for some time that the hippocampus is a key area of the brain susceptible to damage in Alzheimer's disease, and this research links the size of the hippocampus to a person's performance on different types of memory test(s),” says Dr. Laura Phipps of Alzheimer’s Research UK.

The findings highlight the value of studying the hippocampi to understand and diagnose memory problems, as well as the value of using different types of memory tests to “gain a fuller picture of what’s happening in the brain.”

“Brain volume varies from person to person,” she says, “so larger studies will be needed to explore whether this approach could provide consistent and accurate predictions of those at greatest risk of memory problems or dementia.

"Many people will experience mild memory problems, particularly later in life, but knowing who will go on to develop a disease like Alzheimer's is hard to predict. Research to detect the earliest stages of Alzheimer's continues to be an important focus for scientists to be able to identify people at a stage where they are most likely to benefit from future treatments."

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Bonner-Jackson, A. Alzheimer's Research & Therapy, 2015.

Alzheimer's Research UK.

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