Much of what scientists know about the brain has come from two methods. One is play: come up with a test that can measure an ability in a way that doesn't overlap with any other abilities.
The other is to make the best of someone's terrible misfortune—someone who has had a stroke or suffered an accident or had surgery that took out part of their brain. When patients survive these events, they lose some memory abilities but not others. Often the lost abilities can be traced back to specific parts of the brain that have stopped working.
There are multiple types of memory, and each type uses different parts of the brain.
Click or touch a type of memory to learn more
Sensory memory holds a quick flash of everything that our sensory systems—eyes, ears, nose, etc.—take in. It's so short-lived and it packs in so much information that most of it doesn't even make it into our conscious awareness. It's an important first step in the formation of short-term memories, but most of the information will quickly fade away.
Duration: A few tenths of a second up to about 1 second
Sensory information is relayed through the thalamus (except olfaction, which travels directly) to sense-specific areas on the outer surface of the brain (the cortex).
When we see two slightly different images, one immediately following the other, it is very easy to pick out the change. But with a pause in the middle, the information in our sensory memory fades before the next image appears, making it much harder to find the difference.
The first stop for information from the eyes is the visual cortex, an area in the back of the brain. Damage to this area can make patients partially or fully blind, even though their eyes still work normally. Strangely, patients with this type of "cortical blindness" experience "blindsight." Like a person with perfect vision, they still smile when they see a photo of a smiling face—even though they are not consciously aware of what they're looking at. This is probably because the eyes also send signals to other parts of the brain, including the amygdala, which is the source of emotions.
The thalamus is required for basic human consciousness. Without it, sensory information is not sent out for processing, and patients are left in a vegetative state. They are awake but they cannot respond to their surroundings.
Short-term memory holds onto a few pieces of information at a time, around 4 to 9 items. It helps you remember a phone number for long enough to dial it, or remember something your teacher says for long enough to write it down. Some information in short-term memory will eventually be stored in long-term memory, especially if we give it our attention, but most will fade.
Duration: A few seconds to a minute. We can use repetition to remember things for longer, but distraction will make us forget.
Wernicke's area helps us understand language-based information—things that we read or hear. It is connected to the areas of the brain that take in information from the eyes and ears.
We use Broca's area when we repeat information silently to ourselves. Repetition helps us keep information in short-term memory for longer.
The visual association area on the right side of the brain holds visual and spatial short-term memory. It helps us remember images and pictures, and it helps keeps track of where things are in 3d space.
Tests for Short-term memory measure your ability to hold onto multiple pieces of information and repeat them back. You'll do better at these games if you use repetition or mnemonic tricks—both of which use attention from working memory.
The electronic game Simon was popular in the 1970s and 80s. To play, you have to remember and repeat back a series of blinking, colored buttons. Today, you can find electronic versions of this game online or as downloadable apps.
When a viral infection destroyed memory areas deep within Clive Wearing's brain, the brilliant music composer lost nearly all of his ability to form short-term memories (his long-term memory was also profoundly damaged).
Wearing was left with no sense of the past or future, only the present moment. Every time he blinked, he opened his eyes to an unfamiliar scene. Strangest of all, he continually felt like he was becoming awake and aware for the very first time, a pattern that repeated every few minutes.
Read more about Wearing.
Working memory helps us carry out a task, achieve a goal, or solve a problem. It's like a temporary mental work space where we can bring together information from short-term and long-term memory, and then do something with it. For example, to do mental math, we use multiplication rules stored in long-term memory to work on numbers stored in short-term memory.
Complex tasks like driving a car or reading also rely on working memory: we use skills and rules stored in long-term memory, but we also take in and react to new information as we experience it.
Working memory also helps us control our attention—what we experience as concentration. Attention helps us take in and hold onto important information while filtering out distractions. It helps us keep our tasks in mind for long enough to finish them. In terms of memory storage, attention is a big part of what moves information from sensory memory to short-term memory and finally to long-term memory.
Working memory and attention have a limited capacity: there's only so much information we can hold and manipulate in our minds, and there are only so many things we can attend to at once.
The prefrontal cortex is the biggest player in working memory. Often called the "central executive," it is connected to areas throughout the brain, so it can access and process many types of information.
Within the prefrontal cortex, 3 sub-areas are especially important for attention.
In this Selective Attention activity (Flash), you can see how good you are at turning your attention to one voice and ignoring interfering information. The "Where's Waldo?" books and website are more or less a visual version of this exercise.
The Stroop test is a measure of attention. It takes a surprising amount of effort to filter out conflicting information about the meaning and the color of a word. Try our paper version (pdf).
Test the limits of your working memory in Distractown.
Damage from a stroke or an injury can cause "hemispatial neglect syndrome." Patients ignore information from one side of their visual field, usually the left side. They eat the food only from one side of their plate. And when making a drawing, they leave out the left side of a clock, a flower, or even a face—and they are completely unaware that it is missing. The problem seems to be one of attention: the patients take in the information, but they immediately forget it.
Another type of neglect syndrome affects a patient's ability to recognize their own body parts. For example, they may be unable to find or recognize their left arm, or even refuse to acknowledge that it belongs to them!
Damage to PFC
Patients with damage to the prefrontal cortex, or the central executive, often act inappropriately or impulsively. Because they cannot keep goals in mind, they tend to be poor planners and poor decision makers.
Though his story is mainly anecdotal, Phineas Gage is one of the earliest cases in neuroscience that helped scientists understand how damage to the prefrontal area of the brain can change a person's personality.
Read more about Phineas Gage
Long-term memory is what we think of as "permanent storage," sort of like file cabinet or a computer's hard drive. But the brain is different from these things. First, the brain doesn't get full. Even though you may sometimes feel like your brain is about to burst, people don't really reach a point where they need to dump old information to make way for new memories. It's more like a muscle that grows stronger the more you use it.
Second, some long-term memories tend to fade over time, while others are more "sticky." Events that are associated with strong emotions, like a first kiss or a punch in the face, are more likely to stick. Repetition can also make information stick more firmly. Information that we don't revisit, like the capitol of Albania or what we ate for breakfast on November 5th of last year, is more likely to fade.
Duration: Hours to decades
Patient story: HM
HM is probably the most-studied person in all of neuroscience. Because of a childhood brain injury, HM had severe epilepsy. To try to cure him, a surgeon took out a large chunk of HM's brain (including his hippocampi and other nearby areas). The surgery cured the epilepsy, but at a great cost: HM also lost the ability to consciously remember anything for more than a few minutes.
HM's memory was profoundly broken. As he aged, he was repeatedly shocked to see an old man reflected back in the mirror. And even though he worked with one researcher for decades, he never remembered having met her before. Yet HM kept his intelligence, vocabulary, language, and many of his memories from before the surgery.
Importantly, HM's short term memory and his working memory worked just fine. This was an early clue that short-term and long-term memory are separate systems that rely on different parts of the brain.
Event-based episodic or autobiographical memory is your life history. It's your mental record of things that have happened to and around you, like what you ate for breakfast yesterday, or the time you went to your friend's house to watch the movie Frozen and the power went out. Your memory for each event includes sights, sounds, and what you were thinking and feeling at the time.
The hippocampus (we have two, one on each side of the brain) is key for moving episodic information from short-term memory into long-term storage.
The amygdala is the emotional center of the brain. Experiences that are connected to intense emotions make for stronger memories.
The memories themselves are encoded in multiple places throughout the brain. For example, the same areas of the brain that process sights, sounds, and emotions are also activated when you recall the sights, sounds, and emotions associated with an episode from your past.
Patient story: RB
After a series of heart-related events deprived his brain of oxygen, RB started having serious problems forming new episodic and semantic memories. And it seems that only his memory was affected. RB's personality and intelligence were the same, he could still remember facts and events from before the incident, he could still form new procedural memories, and he performed normally on other cognitive tests.
After RB died, doctors examined his brain. They saw that nearly all of the damage was in the CA1 area of the hippocampus. RB's case showed that damage to this small area of the brain was enough to keep him from making new episodic and semantic memories, while leaving other functions intact. The hippocampus is now viewed as an important link in the brain circuit that moves certain types of information from short-term into long-term memory.
Semantic memory is a collection of facts, like Salt Lake City is the capitol of Utah, or dogs are mammals. It also includes things like the meanings of words and the rules of grammar. You can consciously recall the information stored here, but it's not connected to your personal experiences.
The left premotor area stores information mainly about "function," or what it is that we do with something—information that is more likely to apply to non-living things like tools.
The inferior lateral temporal area stores information mainly about "form," or what features we can use to identify something—which generally relates to living things.
The hippocampus and parahippocampus are important for moving semantic information in and out of long-term storage.
Patient story: KC
We know that semantic and episodic memories are recalled separately from one another thanks to patients like KC. KC had a brain injury that damaged part of his hippocampi but left his parahippocampi intact. After the accident, he could no longer access his episodic memories, but he could still recall some semantic memories. While he remembered the facts about his experiences, he remembered nothing about his place in them or his feelings about them. Scientists think that certain parts of the hippocampus are more important for recalling episodic memories, and the parahippocampus is more involved in recalling (and possibly forming) semantic memories.
Read more about KC.
Category-specific memory loss
In some patients, infection with herpes simplex virus can eat away specific areas of the brain, wiping out the ability to recognize a certain class of objects—like fruit, animals, or tools. In most cases, the patients stop recognizing mainly living things (vegetables, animals, flowers). But some patients lose the ability to recognize only nonliving things (furniture, vehicles, clothing). In others, the problems are restricted to more specific categories, like fruits or animals. Even though other brain functions are normal, they may not be able to recall that a lemon is yellow and sour or that a cow says "moo."
These cases show that certain facts are lumped together, either because they are stored in the same brain regions, or because they are connected through shared neural networks.
Procedural memory includes things that are task and skill based. It includes "motor memory" for things like how to write cursive letters or ride a bicycle, as well as more-complex skills like playing a collection of songs on the guitar. Skill-based memories get stronger the more we practice them.
Procedural memory also helps us learn cause and effect. It stores information about foods that make us sick, or actions that are followed by rewards.
The supplementary motor area helps us move our bodies
The cerebellum helps coordinate movements, and it's involved in motor memory.
The striatum, is important for habits and skills that we learn gradually through repetition.
HM and other patients with damage to the hippocampus have severe problems with episodic (event-based) and semantic (fact-based) memory, yet they can form new procedural memories with no problem. HM famously learned to skillfully trace a star while only looking at its reflection in a mirror—even though he had no memory of all the time he spent practicing it. This tells us that procedural memory uses different brain regions than other types of long-term memory.
Huntington disease and Parkinson disease are devastating movement disorders that affect the basal ganglia. As damage increases, patients' movements become either shaky or slow, making it difficult for them to do things like walk or use a fork. Movement sequences that they could once do automatically require effort and focus. Patients also have trouble learning new motor skills.
In patients with damage to the cerebellum, movement is uncoordinated, like in a drunk person. The cerebellum normally coordinates movement by gathering feedback from the joints, muscles, and eyes; continually checking in with the parts of the brain that plan movement; and making adjustments to keep us on track. The cerebellum also helps store motor memories, so that we can get better with practice. When these processes stop working, movement becomes shaky, sloppy, and uncontrolled.
The simplified model presented here is just one of many ways to categorize types of memory. There are other models too, and some of them use slightly different definitions for some of the terms used here.
This model highlights just a few of the key brain regions involved in different memory functions. Since no part of the brain exists in isolation, most types of memory include more areas than the ones listed here. The big idea to take away is that different areas of the brain have different functions.
If you wish to delve more deeply into the types of memory or the brain anatomy involved, we encourage you to explore the references linked at the bottom of the page.