EAST LANSING, Mich. — When it comes to certain areas of the brain, bigger isn’t always better. According to a study at Michigan State University, a larger hippocampus does not always mean an older adult has strong learning or memory skills, or is immune to cognitive decline.
Research has long shown that the hippocampus shrinks as we age, and this shrinkage occurs more dramatically in people with mild cognitive impairment or Alzheimer’s disease. Due to these observations, neuroscientists largely believed a larger hippocampus meant better memory. This is, until a 2004 study showed that the size of the hippocampus isn’t always related to memory performance in older adults. Today, thanks to this new research, scientists are beginning to understand why.
The research team at MSU were able to prove that the size or volume of the hippocampus is only directly related to memory abilities in older people with more intact limbic white matter. Limbic white matter is the complex neural circuit system that connects the hippocampus to the rest of the brain.
“Our findings highlight the need to measure not just the size of the hippocampus but also how well it’s connected to the rest of the brain when we look for physical markers of memory decline in older adults,” says lead author Andrew Bender in a university release. Bender is a professor at MSU’s College of Human Medicine.
These findings could help physicians make more accurate earlier diagnoses of age-related memory disorders like Alzheimer’s, and avoid potential oversights. Some older adults with a larger hippocampus than normal could have their cognitive decline ignored or misunderstood if physicians fail to also consider their white matter connectivity. An individual could have a larger hippocampus for a variety of reasons, such as a high level of education, extensive social and cognitive engagement, or consistent physical activity.
Bender and his team, which included researchers from Hungary and Germany, analyzed two different types of MRI brain scans on over 330 adults. One scan was meant to reveal the size of the hippocampus, while the other evaluated white matter circuitry. These participants also took learning and memory tests. One of the tests required participants to listen to 15 words and write down as many as they could remember afterwards. The participants repeated this same test five times to determine their efficiency at learning via repetition.
The researchers analyzed the connection between how quickly participants learned the words, the size of their hippocampus, and their white matter circuitry. Only older adults who had both a larger hippocampus and more uniform white matter circuitry connecting their hippocampus to the rest of the brain learned faster than all other participants.
“Our findings reinforce a growing perspective that studying age-related changes in learning and memory from a systems perspective appears far more informative in understanding different patterns of brain and cognitive declines than focusing on any single brain region,” Bender says.
Moving forward, the research team want to utilize even more recent data collected on the same participants who returned for a second set of testing two to three years after the experiments used for this study.
“By following people over time, we can see if there is actually change in older adults’ brain structure and whether that is linked with observable declines in learning and memory,” he concludes.
The study is published in the journal Cerebral Cortex.