Memory is the fundamental cognitive process of encoding, storing, and retrieving information, specifically your experiences and knowledge. Some memories last mere seconds before your brain discards them, while others last for years. Some memories are explicit (you consciously recall them, such as what happened on your last birthday), while others are implicit (they’re unconscious, such as the motions you need to take to walk).Your memory is an inextricable part of your identity and crucial for many parts of life, including simply surviving in your environment. But many different issues can cause reversible memory loss, and some can cause permanent memory loss.

What Are the Different Types of Memory?

There are multiple distinct types of memory, each with their own specific characteristics and functions, that can overlap in daily life. The major types include:

• Sensory memory

• Short-term memory

• Working memory

• Long-term memory

• Prospective memory

The shortest type of memory, sensory memory refers to the storage of information that comes in from your senses. Sensory memory acts a buffer for external stimuli that gives your brain the briefest of time to process the incoming information. Your brain then makes a snap decision on which sensory memories to discard and which to put into short-term memory. In effect, sensory memory is crucial to our ability to filter out irrelevant details and focus on those that matter most in the moment.

Each of the five senses has a corresponding type of memory, some studied more than others:

• Iconic memories for sight

• Auditory memories for sound

• Gustatory memories for taste

• Olfactory memories for smell

• Haptic memory for touch

Each of the sensory memories have their own limits for how long they can hold information, from less than a second (iconic memory) to up to four seconds (auditory memory). These memories are why you can “see” an image in your head of something you were looking at right before you closed your eyes or “hear” a lingering sound after it has already stopped.Short-term memory involves information that is held in the brain for a short period of time, typically around 15 to 30 seconds. It allows you to remember the name of someone you just met, what happened moments ago in a film, or a fact you just looked up. Repeating the information over and over again allows you to hold it in your short-term memory longer and help pass it into long-term memory.The capacity for your short-term memory is limited. Research suggests people can only remember seven elements (plus or minus two) at a time, but “chunking” the information — grouping small units of information into larger ones — allows you to hold more. For example, remembering a phone number you just heard until you write it down is easier when you group numbers together. Instead of remembering a phone number as 2-1-2-5-5-5-1-2-3-4, which has 10 elements, you remember 212-555-1234, which has only three elements.On the flip side, your short-term memory can be hindered when you’re exposed to other stimuli while trying to memorize something, particularly if it’s a similar type of information. If you try to remember a phone number while seeing or hearing other numbers, it’s more difficult and you forget it quicker.

You need your short-term memory to navigate many aspects of everyday life. Reading and conversation, for instance, require you to remember the first part of a sentence to understand its entirety, while following instructions requires you to remember specific sequential steps.

People sometimes use the terms short-term memory and working memory interchangeably, but they are actually distinct. While short-term memory deals with the passive storage of information, working memory refers to temporary memory that is being processed, manipulated, or used to complete a specific cognitive task. It is the mental workspace that’s essential for reasoning, learning, comprehension, problem-solving, and other mental processes.Working memory draws information from both your short-term memory and long-term memory. If you are making a mental calculation in your head, your working memory is using numbers and calculations stored in your short-term memory as well as the mathematical processes or equations stored in your long-term memory. Similarly, when you’re making a lengthy rhetorical argument, your working memory uses both new information (what you said a moment ago) and long-stored information (facts backing your argument).

Some experts consider long-term memory to be any type of memory that lasts longer than 30 seconds. Unlike short-term memory, long-term memory may have a limitless capacity that can last years or even a lifetime, allowing us to retain a vast amount of information. It contains the information that makes you who you are, from the facts you know to the events of your past to skills you’ve learned.Long-term memory can be further divided into various subsets. These include:

• Episodic memory

• Autobiographical memory

• Semantic memory

• Procedural memory

Episodic memory is what most people think of as “memory.” It refers to memories of personally experienced events from your past, including the details of the event, the context in which it occurred, and the emotions associated with it. Episodic memory involves remembering by mentally re-experiencing events with the awareness of how it all fits into the story of your life. Events that are more emotionally charged are often more vividly (and more likely to be) remembered.

Episodic memory is an important part of autobiographical memory — the memory of information related to your life as a whole. Autobiographical memories allow you to know who you are, and they include:

• Memories of specific events, such as the time you met your best friend in school

• Memories of more general experiences, such as what middle school was like for you

• Memories of factual details about yourself and your life, such as the middle school you attended, the age you were when you met your best friend, and the activities you did together

Semantic memory is where you store all of your knowledge. It includes the factual information you memorized, such as the definition of words, movies released in your birth year, and the Pythagorean theorem. It also includes information related to other types of memory, such as the individual smells of the state fair you last visited or the feelings you experience while watching your favorite movie. Semantic memories are free of context and do not invoke impressions of past experiences like episodic memories do. For example, because of your semantic memory you can remember the Pythagorean theorem without having to revisit the moment you learned it.While semantic memory involves the things you know, procedural memory involves the things you know how to do. It is your ingrained and unconscious knowledge about how to do something even if you can’t describe the individual steps, such as how to ride a bike or throw a ball. It includes the automatic movements you make (muscle or motor memory) as well as nonmotor skills like creating sentences with proper grammar and syntax without much thought.

Prospective memory, sometimes known as “memory for intentions,” is essential for planning ahead. It involves your plans or intentions that you cannot fulfill presently but need to remember to perform at an appropriate time in the future. This “remembering to remember” is necessary for many everyday tasks, such as remembering to take your medications, attend appointments, and complete assignments. It can be time-based, such as remembering to take your medications at 6 p.m., or event-based, such as remembering to tell your friend something when you see them.Your prospective memory can fail for many reasons, such as not using notes or other reminders when you’re juggling many tasks or not setting a specific-enough intention (e.g., “work out tomorrow” instead of “work out at 3 p.m. tomorrow”).

There are several steps necessary to form long-term memories:

• Encoding

• Storage (or retention) and consolidation

• Retrieval and reconsolidation

The encoding phase starts with stimuli from your senses becoming sensory memories. Your brain discards some of those sensory memories while encoding others, turning them into short-term memories. Attention plays a key role in this process — your brain is more likely to encode something you’re paying attention to (called central details), especially if it has emotional significance. Things you aren’t paying attention to — peripheral details — are encoded poorly if at all.

During the storage phase, your brain preserves or stores the encoded information in your long-term memory. The neurobiological process of forming long-term memories is called consolidation. Rather than happening instantaneously, memory consolidation is spread out over time as your brain strengthens neural connections or constructs new ones to store a representation of the information. Your brain prioritizes central details during consolidation, and your attention and emotional connection to the information affects how strongly it’s stored, explaining why memories are fragmented and incomplete. Our brains evolved to have a “negativity bias” for survival, meaning that memories attached to powerful negative emotions will be stored more strongly.

How much you think about the information and connect it to other stored information also affects how strongly it will be stored in your long-term memory. Thinking about or accessing those memories is called retrieval. And every time you retrieve a piece of information your brain treats it as “new,” well-encoded information that can be associated with new external and internal contexts, such as the place and time when you retrieved the memory along with your mental state. All of that information gets reconsolidated into a new, more strongly encoded piece of information.This process is at work when you’re telling a story and someone adds new details. That new information — even if inaccurate — can get added to your memory of the story when your brain reconsolidates it into a stronger, more permanent memory. So the next time you tell the story, you may well “remember” the incorrect details as if they actually occurred; your memories of something can change each time you retrieve them. This is less likely to happen to memories of highly stressful and traumatic experiences.

Any number of medical conditions and life circumstances, as well as some medications, can disrupt your ability to create new memories or retrieve existing ones. Some of these causes of memory disruption are reversible or controllable, and some aren’t. They include:

• Aging

• Stress, depression, and anxiety

• ADHD

• Sleep deprivation (sleep is an important factor for memory consolidation and retention)

• Alcohol and drug abuse

• Head injury or trauma

• Neurological conditions, including mild cognitive impairment, dementia and Alzheimer’s disease, epilepsy, and stroke (including “silent” ones with no obvious symptoms)

• Vitamin B1 and B12 deficiencies

• Cancer treatment

• Lyme disease

• Thyroid disease, as well as kidney or liver problems

• Medications with cognitive side effects, including antidepressants, antihistamines, and steroids

• COVID-19 (“long Covid”)

• Diabetes

• Blood clots, tumors, or infections of the brain, including from HIV, tuberculosis, and herpes

While memory loss can be a normal part of aging, it can also indicate a more serious condition, such as dementia or Alzheimer’s. See your doctor if you experience:

• Disruptive memory loss, such as repeating questions or forgetting important events or well-known and frequently used information

• Difficulty performing familiar tasks

• Difficulty making plans and solving problems

• Confusion about time or place

• Trouble understanding visual images and spatial relationships

• Language difficulties, such as forgetting or mixing up words

• Inability to retrace your steps when you misplace something

• Changes in judgment and decision-making

• Withdrawal from social activities

• Changes in mood or personality

• Other people noticing changes in your memory

Bottom line: If you’re concerned about your memory, talk to your doctor.

The Takeaway

Memory is a complex and vital function that plays a core role in your life and makes you who you are. Understanding the different types of memory and how they work can help you understand how your brain works and your sense of self. It’s also important to recognize the myriad factors that can negatively affect your memory and to seek medical advice when necessary. The good news: In many cases, correcting the issues that caused your memory loss, such as getting better sleep or treating mental health problems, can improve your memory.