Hippo-what? What’s it called again?

What pops into your head when you see the word “Arctic”? Is it a vast ocean, massive icebergs, or a blanket of snow? Maybe you think of mints, or the hostility with which your boss sometimes stares at you. The question is: how did your brain do that?

Let’s get this out of the way. It’s called the hippocampus, and it’s the reason why you remember the exact moment you spilled X all over yourself Y years ago.

The words “hippocampus” is Greek for horse sea monster, which is a fun way to remember that the hippocampus looks like a seahorse. Humans and other mammals have two, one on each side of the brain. It was the first brain region identified to support memory.

https://commons.wikimedia.org/w/index.php?search=hippocampus+seahorse&title=Special:Search&go=Go&searchToken=9sjfp88gnxf8qmyejaf4dyyjd#/media/File:Hippocampus_and_seahorse_cropped.JPGSea the resemblance? Credit: Wikimedia Commons (anthonyhcole)

Since then, scientists have discovered that it has major roles long-term memory. It’s essential for creating new memories, and consolidating this new information so you can remember it during your finals in three weeks.

In 1985, Harvard psychologist Daniel Schacter split long-term memory into declarative and procedural memory. Tulving, a cognitive neuroscientist and experimental psychologist, further divided declarative memory into episodic and semantic memory.

The divisions of memory. Credit: Jamie Liew

The hippocampus is crucial for declarative memory.

Declarative memory (sometimes used interchangeably with explicit memory) is the conscious recollection and accumulation of information from learning experiences. When someone asks what you had for lunch yesterday, you might think of what you were doing yesterday and who you were with before remembering what you ate.

This is a unique feature of the hippocampus. It structures the declarative memory system through creating relationships between new or existing memories to consolidate that information. Bonjour? Hello. Hippocampus? Seahorse. Arctic? Snow.

I take that back. Arctic? Bucket list. Credit: Flickr (P J Hansen)

Activating any declarative memory will trigger the activation of related memories. It explains why you think of your embarrassing spill when you see someone with a stain on their shirt, and then you remember another embarrassing moment in high school, and suddenly you’re trying to remember if anyone has actually died from embarrassment.

Declarative memory activation can be independent of environment, which just means that at any point in time you can experience the ground-sinking, soul-crushing embarrassment of a childhood (or adulthood) memory. You’re welcome.

But it also means you can relive the happiest moments of your life and be overwhelmed every single time. This is because the hippocampus is part of the limbic system, which attaches emotion to memory.

For most of us, cake and happy times go hand in hand! Credit: Flickr (jshj)

Declarative memory contrasts with procedural memory, which is the unconscious or implicit form of long-term memory. It deals with skills, habits, and muscle memory. You remember how to ride a bike, but you don’t remember every session of cycling you’ve ever had to reach this level of skill. The same goes for when you’re playing an instrument; you’re not thinking about how you learnt to play the song – not the hands cramping after hours of practice, or the teacher’s hands guiding yours –  but how to play the song itself.

Have you ever sat down at a piano and been able to start playing a piece you hadn’t practised in years? Credit: Flickr (Nayuki)

Declarative memory is split into episodic and semantic memory.

In terms of purposely remembering information, this information can be split into past experiences (episodic memory) and factual knowledge (semantic memory).

Episodic memory allows you to time-travel in your mind, and to feel yourself doing it. This results in “autonoetic awareness”, a highly personalised feeling of re-experiencing oneself in the autobiographical past or present. You experience nostalgia as a result of autonoetic awareness.

On the other hand, remembering how many continents there are, or the word for goodbye in Spanish falls under semantic memory. Your semantic memories comprise everything you have ever learned – and can still remember – in class, or during a trivia night.

So, this is your task. Practise your declarative memory skills and try to remember the distinctions between declarative, procedural, episodic and semantic memory. Or maybe just try to remember that there is a seahorse in your brain called the hippocampus. You might find that learning how to make strong associations between information is the quickest way to remember something!

Curious? Learn more here:

10 Responses to “Hippo-what? What’s it called again?”

  1. Jamie Liew says:

    Yay Imogen! My job is done! 😀

  2. Imogen says:

    So interesting!! I have never considered the different types of memory before. I have no doubt that I’ll remember the hippocampus for a long time now 🙂

  3. Jamie Liew says:

    Thanks for the feedback, Claudia. That’s what I was going for with the title!

  4. Jamie Liew says:

    Indeed! There are heaps of ways, but they boil down to rehearsing things in your short term/working memory (e.g. choosing a new PIN number) long enough, and for enough times that it eventually gets sent to your long term memory so that you can still remember it without you having to rehearse that information as much. Here’s a link about how to remember things you usually forget: http://health.howstuffworks.com/human-body/systems/nervous-system/how-to-improve-your-memory3.htm

  5. Jamie Liew says:

    Definitely. It’s strange to think that such a mushy, oyster-resembling seahorse (too much?) is responsible for countless aspects of our lives that we probably take for granted. Thanks for the feedback, Will – glad you got something out of it!

  6. Jamie Liew says:

    Hi Richard! That’s great! I was hoping it would have that effect. Thanks for sharing that paper; I was always under the impression that dreams used memories to help us process our emotion/experiences – in a vague sort of way – so seeing research being done in this area is encouraging!

  7. cshao2 says:

    Wow! Teachers always say to relate a new concept to something you already know, and this is why! I also like how you connected the heading to the content, nice play on meaning.

  8. chambersa says:

    Interesting post! I never realised how many different types of memory there are. I wonder what’s the best way to make sure things you’ve learnt stay in your long term memory?

  9. Will McDonald says:

    While I can see the resemblance between the hippocampus and a seahorse, its still super gross!

    Thanks for a really engaging piece – I had never thought about the different processes related to skills. You pointing out the distinction between “Declarative memory” and “Procedural memory” provided an interesting consideration!

  10. Richard Proudlove says:

    Hi Jamie. Really interesting piece. It motivated me to learn more and I discovered that the hippocampus may also provide the sequential imagery in our dreams (https://www.nature.com/nature/journal/v437/n7063/full/nature04288.html). Fascinating.