The Seahorse That Remembers

Hippocampal failure leads to rapid forgetting.

Posted Jun 15, 2019

In our last article, we reviewed how the frontal lobes contribute to normal memory and what happens when they fail in dementia. In this week’s article we will continue our exploration of episodic memory—memory for episodes of our life—with a look at the hippocampus.

Did you know that the word hippocampus means seahorse in Latin? The anatomists who named this structure noted that the brain structure appeared to have a head, body, and curled tail—just like a seahorse.

The hippocampus forms and stores new memories.

The hippocampus binds together sights, sounds, tastes, smells, thoughts, and emotions into a memory for an episode of your life—such as having coffee with your friend. The hippocampus also stores that memory so you can retrieve it later. In fact, once bound together, thinking about any part of the memory, such as the smell of the cappuccino, can bring the entire episode to mind. That’s why we think of the hippocampus as the memory center of your brain. There’s one on each side, left and right. They are located deep inside your brain, on the inside and bottom of each temporal lobe, which are next to your temples on each side of your head, just behind your eyes. Your left hippocampus is somewhat specialized for remembering verbal and factual information, and your right for non-verbal and emotional information.

Hippocampal damage leads to rapid forgetting.

Anyone can forget they've said something or forget the answer to a question and ask it again. However, when there is a pattern of asking the same questions again and again, or telling the same stories to the same people over and over, that is usually a sign of rapid forgetting. Another example of rapid forgetting is when something important is left unattended, such as the iron being left on or the front door left open.

Even as one gets older, rapid forgetting is not normal and should always be evaluated. Rapid forgetting suggests damage to the hippocampus, where new memories are formed and stored. When the hippocampus is damaged, even if the frontal lobes are properly focusing attention and taking in new information, new memories are either formed imperfectly or not at all.

Losing things and getting lost may be due to either frontal lobe or hippocampal dysfunction.

Although some memory problems are due mainly to poor attention related to frontal lobe dysfunction and some memory problems are mainly due to rapid forgetting from damage to the hippocampus, many other memory problems can be due to either of these causes or both together. For example, one can misplace their keys either because they were not paying attention when they slipped them into their coat pocket, or because they thoughtfully put the keys into their coat pocket but then rapidly forgot they were there.

Getting lost deserves special mention. The reason that individuals with dementia often get lost is that it is actually quite difficult to always know where you are and how to get to where you want to go. If it wasn’t so challenging, people wouldn’t use maps, GPS devices, and phone apps so often! Finding one’s way requires remembering where one wants to go, paying attention as one plans out the route, remembering the route, and paying attention to landmarks as one is traveling—landmarks that need to be recognized from memory. So, getting lost is likely to happen if one has either impaired attention or rapid forgetting—and both are common in dementia.

Together, the frontal lobes and the hippocampus enable planning, organizing, and performing complicated activities.

Planning and organizing events and activities, such as hosting dinner parties or making vacation plans, and learning how to use new electronic devices, software programs, or websites all require many cognitive abilities—including attention and memory—to be working together in a coordinated fashion. Because both attention and memory are needed, both the frontal lobes and the hippocampus need to be working properly. Since just about all causes of dementia impair the frontal lobes, the hippocampus, or both, planning, organizing, and performing complicated activities are almost always impaired in dementia.

© Andrew E. Budson, MD, 2019, all rights reserved.

References

Budson AE, O’Connor MK. Seven Steps to Managing Your Memory: What’s Normal, What’s Not, and What to Do About It, New York: Oxford University Press, 2017.

Budson AE, Solomon PR. Memory Loss, Alzheimer’s Disease, & Dementia: A Practical Guide for Clinicians, 2nd Edition, Philadelphia: Elsevier Inc., 2016.

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