BrainStuff Classics: How Does the Hippocampus Work?

Without the hippocampus, our brains have serious trouble recalling and recording certain types of long-term memories. Learn how this brain structure works in today's classic episode of BrainStuff, based on this article: https://health.howstuffworks.com/human-body/systems/nervous-system/hippocampus.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to BrainStuff, a production of iHeartRadio. Hey, BrainStuff. I'm
Lauren Vogelbaum, and this is a classic episode of the podcast.
In this one, we get into some literal brain stuff
about how the hippocampus works and what can happen when
it doesn't work. Hey, BrainStuff. Lauren Vogelbaum here. When the

(00:26):
movie Memento came out in the year 2000, audiences were
stunned by the unusual storytelling. The film centered on a
protagonist with no long-term memory. Every few minutes, he'd forget
what he had just learned. And to help the audience empathize,
director Christopher Nolan had the story unfold in reverse chronological order.
It gave viewers the opportunity to piece together information the

(00:47):
same way they would if they themselves couldn't retain long-term memories—
And researchers have actually used this effect of this film
to deepen our overall understanding of the memory mechanisms in
the brain. One of the study authors said in a statement,
Memento simulates what it would feel like to be a
person who has suffered damage to the hippocampus that has
obliterated the formation of long-term memories. Even short-term memories last

(01:11):
only a couple of minutes before they're gone. The hippocampus
also gets damaged, albeit to a lesser extent, in cases
of severe and protracted stress as stress hormones gnaw the brain.
Brain nerds, which honestly should probably be all of us,
may know that the amygdala plays a major role in
controlling fear and the cerebellum makes coordinated movement possible. But

(01:33):
how does the hippocampus work? And why does it play
such a pivotal role in keeping our memories safe? We
spoke with psychiatrist Ellen Vora, MD. She explained that the
hippocampus is, quote, part of our limbic brain, a deep,
primitive part of our brain that's associated with emotion and memory.
Located in the temporal lobe, this tiny organ plays a

(01:59):
massive role in the storage of long-term memories and the
memory of the location of people and objects. It's named
for the Greek words hippo, meaning horse, and campo, meaning monster,
which is a word for seahorse because the structure curves
around like a seahorse or horseshoe. We actually have two
hippocampi structures, one in each hemisphere of the brain, though

(02:20):
together they're generally referred to as the singular hippocampus. And yes,
the hippocampus resides in the limbic system, which is associated
with emotions and reactions. As you might expect, people with
Alzheimer's disease have demonstrated damage to the hippocampus. The function
of the hippocampus is perhaps most clear in examples of
patients who have sustained damage to theirs. In the 1950s,

(02:43):
scientists William Beecher Scoville and Brenda Milner described what happened
to a man with epilepsy who'd received surgery on his
hippocampus in an effort to relieve the seizures. He retained
memories from his childhood, but he couldn't form new memories
or piece together when or where things happened. That same decade, Dr.
William Scoville began removing patients' hippocampus. At the time, scientists

(03:06):
knew it helped process emotions, but they weren't totally clear
on how. Scoville wanted to see what would happen if
he removed part of the brain in patients exhibiting certain symptoms,
like seizures. One such patient, referred to as H.M., underwent
the surgery and found relief from his epilepsy, but a
near total loss of memory. In the 1980s, Kent Cochran,

(03:27):
famously known in the psychology and neuroscience worlds as K.C.,
fell off his motorcycle and lost several brain structures, including
his hippocampus. Predictably, he lost most of his memories, but
held on to some specific ones from his earlier life.
All things that seemed rooted in fact and devoid of
emotion or context. Experts later came to call these types

(03:48):
of memories semantic memories. So while patients like KC could
clearly keep a handful of memories intact, most were lost.
Recollections of personal experience are all pretty much a loss
in the damage or removal of the hippocampus. These types
of memories are now known as episodic memory. KC, for example,

(04:09):
could remember that his brother had gotten married, and he
could recognize family members in photos from that day, all
facts based in semantic memory. But he couldn't remember his
family reacting to the perm he had gotten for the occasion,
which is episodic memory. Over time, scientists came to understand
that the hippocampus is involved in two types of memory,

(04:29):
declarative and spatial. Declarative memories are the ones associated with
facts or events. Semantic memory is considered one type of
declarative memory, and episodic is another type. The hippocampus is
also involved in spatial relationship memories, the kind related to
roots and pathways. And it's also where short-term memories are
turned into long-term memories, which are then stored elsewhere in

(04:51):
the brain. Different types of illness and accidents can damage
the hippocampus. Doctors generally aren't removing the hippocampus for experimentation anymore,
like in the case of HM, though. Alzheimer's disease is
perhaps the most notorious destroyer of the hippocampus, as the
condition has been correlated with atrophy or shrinking of that
area of the brain. As in the case of HM,

(05:14):
epilepsy is also known to affect the hippocampus. Studies have
shown that between 50 to 75% of patients with epilepsy
have hippocampus damage. Two other serious threats to the hippocampus,
as mentioned above, are severe depression and stress. Studies have
demonstrated that the hippocampus can shrink by up to 20%
in people with severe depression, and reviews of studies found

(05:35):
that people with severe depression may have hippocampi that are
an average of 10% smaller than in those people without depression.
Vora said, It's a part of the brain that's very
susceptible to stress. We see it lose volume under conditions
of chronic stress and depression. Conversely, you can restore your
hippocampus with meditation and stress management. You want a healthy

(05:56):
hippocampus so you can remember things. A 2016 review of
studies found that exercise in old age may have the
ability to help strengthen the hippocampi's ability to generate new cells,
which could, in turn, help prevent cognitive decline. It's still
unclear how and why this works, but researchers are continuing
to investigate the connection. A 2017 study also found that

(06:19):
the hippocampus may play a role in many more functions
than memory and pathfinding. The tiny organ may also have
a part in enhancing the responsiveness of vision, touch, and hearing.
Thanks to the continued new findings, some have begun referring
to the hippocampus as the heart of the brain. Today's

(06:40):
episode is based on the article, Without a Hippocampus, Your
Long-Term Memory is History, on HowStuffWorks.com, written by Michelle Konstantinovsky.
BrainStuff is a production of iHeart Podcasts in partnership with
HowStuffWorks.com and is produced by Tyler Clang. For more shows
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or wherever you listen to your favorite shows.