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A Reduction in the Hippocampus in the Brain Linked to Cognitive Decline Risk

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11/21/2023
medicalnewstoday.com

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The pathways in the human brain are similar to a road system. Felix Cesare/Getty Images
  • Researchers report that as the hippocampus area of the brain shrinks, memory worsens.
  • They note that the decline in hippocampus volume could be due to different forms of dementia, not just Alzheimer’s disease.
  • The hippocampus helps individuals form new memories.

Hippocampus atrophy may be associated with cognitive decline.

In fact, researchers in a study published today in the journal Neurology report that the faster the atrophy process, the faster the decline.

They add that problems with memory could be attributed to hippocampus shrinkage, but not all people with signs of this condition have Alzheimer’s disease.

In their study, researchers analyzed the number of amyloid plaques, tau tangles, and hippocampus volume in 128 people.

The participants, with a median age of 73, did not have cognitive or memory problems at the start of the study. Of the participants, 56% were women and 44% were men. All study subjects had brain scans annually for 10 years.

The researchers said that a faster decline in the size of the hippocampus was associated with a more rapid cognitive decline. The scientists also found that hippocampus atrophy was independent of amyloid plaques and tau tangles increases.

The shrinkage of the hippocampus alone accounted for 10 percent of the difference in cognitive function, they said.

“This is an interesting study, showing us that not only amyloid-beta plaques in the brain but also decreasing the size of the hippocampus leads to memory loss,” said Dr. Shae Datta, the co-director of NYU Langone’s Concussion Center in New York and director of cognitive neurology at NYU Langone Hospital—Long Island.

“The rise of new drugs that can target the amyloid-beta plaques in the brain that are an early sign of Alzheimer’s disease would not work on patients that did not have the amyloid-beta plaques and instead had hippocampal atrophy,” Datta, who was not involved in the study, explained to Medical News Today. “This is why this study is important [it reminds us] to find the cause of dementia in the patient that we are treating. In older adults, they [the researchers] saw shrinking of the hippocampus lead to memory loss, even if they did not have Aβ or tau, suggesting that non-AD pathologies can also lead to hippocampal shrinking.”

The researchers noted that further medical tests should examine whether the decline in hippocampus volume is from Alzheimer’s disease or a different cause.

“Measuring the hippocampus by itself would not result in a specific diagnosis,” said Dr. Douglas Scharre, a professor of clinical neurology and psychiatry at The Ohio State University Wexner Medical Center and College of Medicine and Director of the Division of Cognitive Neurology and the Center for Cognitive and Memory Disorders.

“It might predict response to medication if the cause of the hippocampus atrophy were due to Alzheimer’s disease or Lewy body disease,” Scharre, who was not involved in the study, told Medical News Today. “Most other non-Alzheimer’s conditions causing hippocampal atrophy are not very amenable to medications.”

A meta-analysis completed in April 2023 reported that drugs used to reduce amyloid plaques can accelerate the loss of brain volume. The study researchers recommended that physicians monitor brain volume changes for patients taking these medications to determine if continued treatment is warranted.

“I think this is an excellent and very informative study,” said Dr. Marc Gordon, the chief of neurology at Zucker Hillside Hospital in New York and a professor of neurology and psychiatry at the Donald and Barbara Zucker School of Medicine at Hofstra/Northwell.

“For me, the main takeaway from this study is that not every person who has memory issues and shrinkage of the hippocampus has Alzheimer’s,” Gordon, who was not involved in the study, told Medical News Today. “And not everyone diagnosed with Alzheimer’s has it. Or, they may have Alzheimer’s and something else. It is a reminder to be open-minded and look at other possible causes for forgetfulness before making a diagnosis.”

Some of the limitations of the study included:

  • The participants were highly educated and white, making it difficult to generalize the results to other populations.
  • The pre-trial testing did not include early Alzheimer’s. The researchers suggest further studies should include younger people to map the development of Alzheimer’s as it relates to the hippocampus.
  • The researchers noted that more extended studies or more observations per participant could potentially lead to different conclusions.

The hippocampus plays a role in memory.

“The hippocampus (there are two in the brain, one on each side) is a brain structure found deep inside the brain. It is critical in forming new memories,” said Dr. David Merrill, a geriatric psychiatrist and director of the Pacific Neuroscience Institute’s Pacific Brain Health Center in California.

“Without the hippocampus, you could be introduced to someone, leave the room for a few seconds, then come back and need to be introduced again because you have no memory of meeting them,” Merrill, who was not involved in the study, told Medical News Today. “In the later years, the hippocampus can shrink in size and volume. Often, this is caused by dementia, but not necessarily Alzheimer’s. It could be another form of dementia, such as vascular, brain lesions, or age-related tauopathy. As it shrinks, memory continues to worsen.”

Exercise helps to keep the hippocampus working properly. Regular exercise promotes the growth of new neurons, which are incorporated into the hippocampus, according to a 2018 report published in the Frontiers of Neuroscience. In it, researchers said they believe this process improves cognition and emotional regulation.

Another study found that exercise increased the size of the hippocampus, even in adults.

Diet is also essential in keeping the hippocampus healthy and helping it increase in size. “A low glycemic or Mediterranean diet is good for brain health,” Merrill said. “The quality of your diet is reflected in your brain. Like exercise, eating well can increase the size of your hippocampus.

“If I had to sum up keeping your brain healthy,” said Merrill, “it would be good nutrition, regular exercise, and regular socialization.”

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