Your Brain’s "Save" Button: The Amygdala

Abstract

Do you ever wonder why you remember some experiences better than others? Why you remember that funny joke your friend told at lunch a few months ago or the scary snake you saw in your backyard, but not that time you went to the post office with your parents? Just like a computer has a save button, our brains do, too! When something scary, exciting, or strange happens, a small part of the brain, the amygdala, helps us click save on that event so we can remember it later. Decades of research have helped scientists understand what parts of the brain are important for memory and how the amygdala works with other brain regions to tag experiences as worth remembering. This research is important for understanding how memories are formed and can help us create new therapies for people with memory problems, who have trouble forming new memories and remembering past experiences.

You go to school every day, but some school days are remembered better than others. What makes one day more memorable, and how does your brain save that experience to be remembered for a long time? Much like a computer has a save button for when we want to store a picture or a movie, our brains do too! Although we usually forget most of our daily experiences, if something funny, scary, or strange happens, our brain has a way of clicking save on that event so we can remember it later. This ability is essential for remembering important things that happen in our lives that might influence how we act in the future.

There are many different parts of the brain that are important for our memories, but the amygdala is at the center of the saving process. When something eventful happens, the amygdala functions as a sort of alarm system that tags the highly emotional experience as worth remembering (1)(2). Regardless of what happened or where it happened, when the amygdala is highly active after an event, you are more likely to form a strong, long-lasting memory. However, these memories are not like making a video recording of the experience. It’s more like if a recording was chopped-up into the sounds, smells, feelings, and sights you were experiencing during the event. Later, when you are reminded of the experience, your brain puts these chopped-up details back together into a story that feels like a video you can remember or share with someone else. (And when you can’t remember certain details, your brain fills in the gaps with what might have happened!) The amygdala makes it more likely you will later remember those sounds, smells, feelings, and sights when you experience them. This is sort of like hitting a save button on your phone or computer.

The Save Button

The amygdala is one small but influential part of a larger network of brain areas involved in learning and memory. When the amygdala gets activated, it tells a neighboring part of your brain, the hippocampus, to make note of the many different brain regions that were activated by that experience. All those pieces of the memory can be saved and put back together later when you remember the event. This is a little bit like recording a small snapshot of a virtual class for school (Figure 1). The virtual meeting is underway, and your teacher starts talking about something really important, like a lesson about the brain, that you know you’ll want to remember later. You hit the big red “Record” button on the screen. As the meeting continues you can see all the other kids in your class in their video bubbles on the side of your screen. You can also see students typing questions into the chat box while your teacher talks. Occasionally, a student will use the thumbs-up reaction emoji to let the teacher know they understand what is going on. You stop the recording after a few minutes, and it gets saved to a folder on your computer that contains each piece of the recording. The video, the audio, the chat thread, the emojis, and the list of participants, each get saved as individual files to this folder. This folder is similar to how the hippocampus stores each part of an experience so you can remember it later. You can think of the amygdala as being important for telling the brain when to save an experience, and the hippocampus as being the part of the brain that is important for knowing where the memory is saved. Without this amygdala save feature, your virtual class meeting would be lost. But hitting the record button tells your hippocampus and the rest of your brain to make a memory for the different pieces of that class experience.

Figure 1 –

Illustration of how the amygdala acts like your brain’s save button.

The amygdala is like the save feature of your virtual meeting for class. Clicking the recording button will save everything that was happening during the class, like the lesson about the brain your teacher was showing onscreen, the conversations in the chat, the list of participants who attended, and the audio and video recordings from the meeting. Each of these different parts of the class recording are saved to a folder on your computer so you can watch them again in the future. The hippocampus acts like this folder because it stores all the pieces of an experience so you can remember later. You can think of the amygdala as the part of the brain that tells when to save an experience, and the hippocampus as being important for where all the components of that experience are stored. (Created with BioRender.com)

Activating your Amygdala

This almond-shaped amygdala is a brain region deep behind your ears near the middle of the brain. Part of the amygdala called the basolateral amygdala gets activated during emotional experiences. When something exciting happens, like getting surprised by your friends for your birthday, the glands on top of your kidneys called adrenal glands release a substance called epinephrine, also known as adrenaline (Figure 2). This output of adrenaline, through a chain of connected structures, causes the locus coeruleus to release another substance, norepinephrine, directly into your basolateral amygdala causing it to be activated (3). The activation of your amygdala by this rush of norepinephrine will click save on this experience making it more likely you will remember this birthday party for longer.

Figure 2 –

The cascade of events that activates the amygdala.

When something exciting happens, like getting surprised by your friends for your birthday, the adrenal glands on top of your kidneys release epinephrine that activates a region in your brainstem, the locus coeruleus, which is responsible for releasing another substance, norepinephrine, directly into your basolateral amygdala causing it to be activated. All of this allows you to remember your birthday and the other things that were happening around you at the time of the party. (Created with BioRender.com)

How Did We Discover the Brain’s Save Button?

Because animals like rats have a lot of the same brain regions and connections between those regions as our human brain does, they are a great model for figuring out how the brain works. For example, scientists know the amygdala is important for saving your memories based on decades of research using artificial ways of activating the amygdala in the rat brain. In some experiments, researchers have shown that injecting norepinephrine into a rat’s basolateral amygdala causes the rat to better remember the spatial layout of a room so it can navigate better in the future (4). Similarly, in experiments where scientists have surgically placed metal electrodes into a rat’s amygdala, applying a tiny amount of electrical stimulation to these pieces of metal influences the amygdala and improves memory for the objects the rat previously sniffed and saw (5). Sometimes humans who have seizures also have electrodes implanted into their brain in the hospital to figure out why they are having seizures. Researchers have found that low levels of electrical stimulation of the basolateral amygdala in these patients (about 1/1000^th the strength of a flashlight) increases memory for pictures the people were shown on a computer screen (6) (Figure 3). This suggests by artificially pressing the save button in both rodents and people, we can make the brain more likely to remember experiences.

Figure 3 –

The effects of human amygdala stimulation on memory.

In human patients with electrodes implanted into their brain, a low amount of electrical stimulation to the amygdala immediately after the person sees a picture on a computer screen (during memory encoding), causes them to remember that picture better the next day during a memory retrieval test (top row). Pictures that are not paired with amygdala stimulation during memory encoding are not remembered as well the next day during retrieval (bottom row). (Created with BioRender.com)

Researchers can also learn a lot about the function of a particular brain region by preventing that region from working. For example, rats given an injection of a drug that stops norepinephrine from activating the amygdala had a difficult time remembering a prior encounter they had with a set of objects (7). These studies highlight the importance of the amygdala in saving memories, and suggest that without this brain region, experiences are less likely to be remembered for very long.

Save vs. Storage

Turning down the activity in the amygdala can worsen memory and turning up activity in the amygdala can improve memory. However, researchers don’t think this is because memories are stored in this part of the brain. Instead, the amygdala is known as a modulator or influencer of memory because it affects a variety of other brain regions that are responsible for storing the memories. The striatum, for instance, is an important part of the brain for forming new habits (that’s right, making a new habit is a different type of memory). When you learn to tie your shoes and don’t have to think very hard anymore to tie them, this type of memory is stored in the striatum. When you smell pumpkin pie wafting out of the oven and suddenly remember the holidays last year and being with your family, this odor memory is stored in your olfactory cortex. When you are at a really cool place and listening to some music you love, those memories are stored in your visual and auditory, or seeing and hearing, brain areas. And when these different brain regions are activated during these complex experiences, the amygdala tells the hippocampus to keep a record of those regions that were involved during the event. These regions can then be reactivated later when you remember. Much like the save button on your computer is universal no matter what information is being stored or where the information is being stored, the amygdala clicks save on all sorts of experiences we have by communicating with other brain regions to ensure the information is saved for later.

Scientists even know at the most basic level how this communication between the amygdala and other brain regions works! Each brain region is made up of small cells called neurons that can send signals to each other. Much like you can send texts on your phone to communicate with family or friends that live in other cities and states, neurons in the amygdala can send electrical messages to the neurons in the hippocampus to save an experience. The amygdala can also communicate with the hippocampus to save a memory by influencing proteins that are important for memory in this region. When your amygdala is activated by an emotionally intense experience, the amygdala’s electrical signals can activate chemical signals causing these memory proteins in the hippocampus to be expressed. These memory proteins strengthen the connection between neurons and help save the memory better (8). Both the electrical and protein communication between the amygdala’s neurons and other parts of the brain are what we think helps these memories to be saved and not forgotten. However, because these experiments are difficult to do in humans, more research in the future is needed to explore this idea more.

Conclusion

Some things that occur in our daily lives are more memorable than others, and the amygdala is essential for clicking save on all the pieces of these experiences. When something eventful happens to us, norepinephrine gets released into our basolateral amygdala, activating it, and causing the neurons there to send messages to other brain regions, like the hippocampus, to remember that experience for later. Even though many different brain regions are activated by an experience, the amygdala can tell the hippocampus to keep a record of those regions so they can be reactivated later when you need or want to remember the event. Scientists are still studying the ways the amygdala is important for saving our experiences so they can better understand how the brain makes long-lasting memories. This kind of research is not only important for understanding how the brain works, but also might help us develop treatments to help people with memory problems that have lost the ability to make new memories or remember old memories. After all, memory is a critical part of how we know who we are (or our identity) and define the world around us. Our brain’s save button, the amygdala, allows us to capture the unique and important experiences that happen in our lives so we can make good future decisions.

Glossary

Hippocampus

a seahorse-shaped part of the brain that is important for activating other brain regions during memory retrieval to help put the pieces back together so you can remember.

Basolateral Amygdala

a part of the amygdala that is activated during emotional events and connected with many other brain regions important for learning and memory.

Adrenal Gland

small, hat-shaped organs that sit on top of each kidney that release a hormone, epinephrine, when something scary or exciting happens to you.

Epinephrine

also known as adrenaline, this hormone is released by the adrenal glands and is part of your body’s quick response to danger, excitement, fear, and even stress.

Locus Coeruleus

a small brain region located deep in the brainstem that releases a chemical, norepinephrine, all throughout the brain. This region is generally important for your brain’s response to stress and panic.

Norepinephrine

a chemical released by a brain region called the Locus Coeruleus that activates the amygdala during emotional experiences and helps you remember things for longer.

Electrodes

pieces of metal that can be surgically implanted into the brain that allow scientists to deliver electrical current to specific brain regions to help determine how those brain regions are important for things like learning and memory.

Seizures

unusual electrical activity in the brain that happens suddenly and can cause a person’s muscles to tighten, causing them to pass out, shake, or fall down. In more mild cases, seizures can cause a person to stare off into space or have jerking movements in one part of the body.

Striatum

a part of the brain that is important for movements and motor memory. This region allows complex movements like kicking a soccer ball or tying your shoes to eventually become second-nature or habit.

Olfactory cortex

the region in your brain that is essential for sense of smell and can store memories related to different scents.

Neurons

a type of cell in the brain that act like messengers; communication between neurons helps us learn, remember, move our bodies, see, hear, smell, and other important bodily functions.

Protein

a molecule that makes up many body tissues, like muscles, or hair, and is also important for forming memories. Memory-related proteins in the brain can make the connection between brain cells stronger to help strengthen memories.

Biographies

Author Biography

Krista L. Wahlstrom

I am a Postdoctoral Research Associate in the Immersive Neuromodulation and Neuroimaging Laboratory in the Department of Psychology at The University of Utah. I received my college degree in Biology and Psychology from Luther College in Decorah, Iowa, and my doctorate in Psychology from The University of Iowa. I am interested in how the amygdala helps us make long-lasting memories and the ways that electrical stimulation of the human amygdala can enhance different types of memory. Outside of the lab, I love to play soccer, scuba dive, go hiking, play the piano, and sing.

Cory S. Inman

I lead the Immersive Neuromodulation and Neuroimaging Laboratory in the Psychology department at the University of Utah. I received my college degree in Psychology from Georgia State University and my doctorate from Emory University. I completed my first postdoctoral fellowship in the Neurosurgery department at Emory University and a second postdoctoral fellowship at UCLA. I have broad interests in helping to establish approaches that push our understanding of emotion and memory from the laboratory into the wild, real world. Outside of the lab I spend my time playing with my two kids, playing basketball, playing guitar, and going on outdoor adventures like white water rafting, snowboarding, hiking, and climbing.