You may not realize it, but you experience the effects of the limbic system every single
day.
Whenever a horror movie frightens you and your heart starts to pound, it is the limbic
system kicking into high gear.
Goosebumps and hunger pangs also partly come from this system.
Memories arise here, and movies like Memento and 50 First Dates show what can happen when
a part of the limbic system is damaged.
The limbic system is where our initial emotional responses originate.
It is primarily associated with emotions such as fear, aggression, sexual attraction, memory,
learning, and smell.
The name “limbic system” comes from the Latin word limbus, which means border.
Physically, the limbic system lies at the border of two parts of the brain—the neocortex
and the brainstem.
It acts like a bridge between the neocortex—the part of the brain that helps us to think,
reason, and consciously process our emotions—and the brainstem—a part of the brain that does
the autopilot work of keeping the body alive without conscious thinking.
So, to which part of the brain does the limbic system belong?
Well, the limbic system is not one part, but rather a collection of different parts of
the brain that scientists have grouped together.
However, scientists have not reached a consensus on which parts should compose the limbic system.
With that said, some important parts of the brain are central to the limbic system: the
thalamus, hypothalamus, amygdala, and hippocampus.
An important point here is that, although we say "parts of the limbic system," all of
these structures are connected with each other and with other parts of the brain, such as
the cortex.
The thalamus The thalamus is called the relay center of
the brain.
It decides which sensory inputs must go where, or whether the brain should ignore something
altogether.
Imagine you’re watching a horror film.
The optic nerve in your retina will relay the visual information to the thalamus, which
then decides whether that information is important enough to pay attention to.
If so, it sends the information to the relevant parts of the brain.
This occurs for most senses except our sense of smell.
Olfactory information goes directly to the olfactory bulbs, but there is evidence that
the olfactory bulbs are connected to the thalamus.
You can check out the description box to learn more.
The amygdala The amygdala is a small almond-shaped structure
responsible for fear, anxiety, aggression, sexual attraction, and pleasure.
The fear that you feel during a horror movie or when you stand on the edge of a cliff is
due to the amygdala.
The attraction you may have to someone is also partially due to the amygdala.
Think of the amygdala as your built-in spidey sense.
The hypothalamus The hypothalamus is the critical connection
between the brain and the body.
It releases its own hormones and also controls other glands to bring about necessary changes
in the body.
It is responsible for maintaining homeostasis or balance in the body.
It regulates the sleep-wake cycle, body temperature, and hunger, and is also the reason why your
body can "feel" the emotions of your brain.
For example, in response to a horror movie, the hypothalamus receives a signal from the
amygdala that something frightening is being presented.
The hypothalamus then triggers the fear response, better known as the flight or fight response,
or an adrenaline rush.
For this reason, the hypothalamus is called the "master regulator of the endocrine system".
The hippocampus The fourth and final structure is the hippocampus.
This structure looks a bit like a seahorse—hence the name, which means seahorse in Greek—and
is mainly related to learning and memory, especially in converting short-term memory
into long-term memory.
Thus, your childhood memories have a long life due to the hippocampus.
The hippocampus also allows you to remember important facts for your exams!
We know the limbic system's functions, in part, because of the behavior of humans and
certain animals when these parts are either completely or partially damaged.
If the amygdala is partially damaged, an individual feels less fear, becomes hypersexual and mellow,
among other symptoms.
Medically, this is called Kluver-Bucy syndrome.
SM is a patient whose amygdalas were both destroyed.
The patient could famously not feel fear, nor could she recognize it in other people.
Researchers made her hold snakes and spiders, showed her horror films, and even took her
to a haunted house, but she showed no signs of being afraid.
Those with a damaged hippocampus cannot convert short-term memories into long-term ones, which
means they will only be able to remember something for a few minutes or even seconds before forgetting
it.
All the memories formed before the hippocampus is damaged are secure, but no new ones can
form.
This condition is called anterograde amnesia, most popularly seen in the movies Memento
and 50 First Dates.
Depending on the extent of the damage and which parts of the hypothalamus have been
damaged, the consequences can include changes in appetite, temperature control, sleep, and
mood.
Lastly, results of damage to the thalamus may include loss of senses, decreased balance
and coordination, and pain-related issues.
The effects depend on the extent of the damage and which part of the thalamus has been damaged.
Today, we study the brain using brain imaging techniques like fMRI and PET scans, and we
can even look into the brain’s neurons and molecules.
We have discovered so much about the brain and the limbic system in this way, but there
are so many more questions still left to be answered.