Memory 101: From Systems to Strategies
Memory is the cornerstone of human cognition. It allows you to store and remember large amounts of information and skills. Memory processes are complex, made up of multiple unique yet interconnected systems that span several brain areas. This article breaks down memory at every stage, outlines the main memory centers in the brain, and provides every day strategies to help you enhance your memory.
What is memory?
Every second, the brain is bombarded with 11 million bits of information (1). With so many inputs, the brain needs a way to understand this intel. At the basis, memory is the brain’s mechanism for processing, saving, and remembering information, enabling you to remember a vast amount of experiences, facts, and skills.
One way to think about this is to imagine your brain as a huge library, with shelves upon shelves filled with millions of books. Each book represents something you experienced, felt, saw, heard, touched, or something you learned how to do. Before you can, so to speak, pull books of the shelf, these memories first need to get recorded in the brain. This memory formation occurs in several stages (2,3).
Encoding. The first step in memory formation is encoding, where all incoming sensory information is transformed into a format that the brain can understand. This format is a complex pattern of neural activity where sensory inputs are translated into electrochemical signals which the brain can “read.”
Storage. Once encoded, memories go in different brain regions. Think of this stage as a filing system, with different types of memories stored in different areas. Some memories are temporarily held in sensory memory, providing a brief snapshot of the present moment. Other memories are consolidated into long-term memory, where they can remain potentially forever. More on these systems later.
Retrieval. The final stage of memory formation is retrieval, where stored memories are brought back to awareness. Retrieval is like searching for a specific book in your mental library; sometimes, the memory comes readily to mind, while at other times, it may require more effort to pull out.
Reconsolidation. There is also a fourth, and less studied, memory stage is where memory becomes temporarily unstable when it’s in the process of being retrieved, making it prone to change. In this reconsolidation phase, memories can get updated and changed as new information comes in.
Essentially, memory is the foundation of identity, shaping who you are and how you interact with the world. It allows you to learn from the past, plan for the future, and navigate the complexities of daily life. Without memory, each page of our books would exist in isolation, disconnected from the rich library of experiences that make up life.
Memory Systems
Human memory can be classified into two major systems comprising of short and long-term memory. These systems are interconnected but do different things, allowing you to process and remember different types of information (Fig. 1).
Short-term Memory (STM)
Short-term memory is where information is held for brief periods of time. This system allows you to temporarily store and manipulate incoming sensory information, like solving math problems or holding a lively conversation (2,3).
Going back to the grand mental library analogy, think of STM as quickly pulling out a book from a smaller shelf and talking about it before putting it back. STM capacity is limited, and information not actively rehearsed or transferred to long-term memory is in danger of being replaced by new stimuli coming in.
STM is made up of:
Sensory Memory. Picture yourself standing in a rainforest, surrounded by exotic plants, chirping birds, and colorful flowers. Before any of this information can be processed, it first needs to go through sensory memory. Sensory memory acts as a temporary holding area, preserving sensory input for a fraction of a second to a few seconds before it either fades away or gets transferred to the next stage of memory processing.
Working Memory. As sensory memory filters through incoming inputs, some of these items find their way into working memory, which is a kind of mental workspace where you can hold information for 30 seconds to a few minutes. Working memory allows you to juggle multiple pieces of information simultaneously, such as remembering a phone number or someone’s name you just met.
Long-Term Memory (LTM)
Where STM is transient and short-lived in nature, LTM is lasting and durable. Just as books in the library can remain for years, decades, or even a lifetime, long-term memories can remain forever because LTM is virtually limitless in capacity and duration. LTM is divided into two main types: declarative (explicit) memory and non-declarative (implicit) memory (2).
Declarative Memory
Declarative memory refers to the conscious, explicit recall of facts, events, and concepts that can be verbalized. In other words, this memory is for things you consciously need to bring back to mind, or “declare.” It plays a crucial role in tasks such as recalling historical events, solving theoretical problems, and understanding language.There are two different types of declarative memory, episodic and semantic.
Episodic Memory. Episodic memory involves the recollection of specific events or experiences that occurred at a particular time and place in your life. These memories are basically a mental "replay" past events—they are rich in detail and allow you to relive emotions. Examples include being able to remember what happened on your college graduation day or a family vacation.
Semantic Memory. Semantic memory, on the other hand, is for general knowledge about the world, including facts and concepts. Unlike episodic memory, semantic memory is not tied to specific personal experiences but is more like a database of knowledge you accumulate about the world. Examples include knowing that Paris is the capital of France or that the Earth orbits the Sun.
Non-declarative Memory
Declarative memory is conscious, it needs a sense of awareness to draw out those memories from our mental library. Non-declarative, or implicit, memory on the other hand, is information that you don’t need conscious awareness for. This type of memory is for things you just know without needing to consciously bring back to mind, like riding a bike or tying your shoes. The main types of non-declarative memory are outlined below.
Procedural Memory. Procedural memory is the ability to learn and execute motor skills, habits, and procedures without conscious awareness of the underlying rules or processes involved. This is like when you learn to ride a bike, type on a keyboard, or play an instrument. Procedural memory relies on repeated practice and reinforcement to develop automaticity.
Priming. Priming occurs when a stimulus (e.g., a word or image) subconsciously influences the processing of a related stimulus presented later. For example, if participants are asked to view the word "dog," they may get primed to recognize related words or images such as "cat" or "paw" more quickly than other images presented later.
Classical Conditioning. Classical conditioning is when you learn to connect one thing with another, leading to a learned reaction to something that used to have no meaning. For example, if a dog that hears a bell every time it's fed, the bell doesn't mean anything special to the dog at first. But if the bell is always followed by food, the dog learns to expect food when it hears the bell. So, eventually, just hearing the bell makes the dog start to drool, even if there's no food in sight. Classical conditioning is for understanding learned behaviors and emotional reactions.
Fig. 1
Diagram of the major human memory systems.
Memory and the Brain
With all these different systems, you might be wondering how everything gets organized into coherent memories that we can recount to others. Luckily, the human brain is a remarkably organized structure, with distinct regions and networks working together to support all the different life experiences you never want to forget. The two main brain areas involved in memory processing are the prefrontal cortex (PFC) and the medial temporal lobe (MTL) area (Fig. 2).
Situated at the front of the brain, the PFC oversees executive functions and working memory. These areas are essential for prioritizing information. The PFC is like the control center of your brain. It helps you keep important information in mind and guides you in setting goals and figuring out how to solve problems (3, 4). Additionally, some areas of the PFC are also shown to be involved in remembering emotional experiences in our lives (5).
The medial temporal lobe (MTL) is a set of brain structures critical for declarative memory (6). The MTL includes structures like the hippocampus, which plays a huge role in the formation and consolidation of new memories and in creating well-organized memories (6, 7). The MTL also includes the amygdala, which tags events as important and also detects threats in the environment (8). These areas work closely with the outer layer of the brain (called the neocortex) to create and maintain long-term memories (6, 9).
Fig. 2
Side-slice of the brain depicting locations of the PFC and MTL involved in memory processing.
Factors Influencing Memory
Memory is not static and some memory processes are subject to change from the environment. Things like what’s happening around you, what you pay attention to, how you feel, and even how old you are can all play a huge role in how memories get processed. This section outlines some of the biggest factors that impact memory.
Attention
Attention determines which information is selected for processing and storage. When attention is focused on relevant things, encoding processes are enhanced, leading to better memory. For example, in one study, participants were asked to selectively attend to either color or location information of study items while undergoing a brain scan. Later memory tests revealed that activity in brain regions associated with color or location processing was improved when participants paid attention to the relevant features (10). When you focus our attention on something, you remember it better later.
However, attention can also hurt memory. Divided attention, or distractions, can lead to poor memory because they limit the brain's ability to process information. When you are trying to focus on too many things at once, there’s fewer mental resources to encode and store new information effectively. This can result in incomplete or inaccurate encoding of the information, making it harder to retrieve later (2, 3).
Emotion
Emotions have a profound influence on memory. Research has shown that memories associated with strong emotions are often more vivid and can be remembered better than other types of memories (11). For example, if you were born before 2001, you likely remember the devastating attacks on the World Trade Center on September 11, 2001. When people are asked to remember such an emotional event, they typically can recount exactly where they were, what they were doing, and many other details relating to that experience. This is because the more emotional events are, the more they activate brain areas such as the amygdala (3, 6, 11), and the more engraved in memory they become.
However, emotion can also lead to remembering the wrong things. For example, in a series of studies, researchers explored how easily our memories can be distorted. Participants were asked to explain their answers after being given false information. Surprisingly, between 15% to 27% of participants claimed to remember seeing items they had only read about but not seen, showing how easily memories can be altered (12, 13).
Stress
We all know stress is bad, but did you also know it can impact your memory? Being chronically, or constantly, stressed out or going through major bad life experiences can have equally bad effects on memory and other areas of daily life. For example, stress experienced while you’re still in the womb leads to increased stress reactivity and reduced physical volume of the hippocampus, affecting learning and making you more vulnerable to anxiety and depression later in life (14). Likewise, maternal separation increases stress hormones, negatively affecting memory and other cognitive functions into adulthood (14). This is because prolonged exposure to stress hormones leads to issues in memory centers in the brain.
However, stress can sometimes also be a good thing because it motivates and energizes people. For example, in sports or competitive situations, stress can enhance performance by sharpening reflexes and boosting adrenaline, leading to improved physical and mental abilities. Additionally, in emergencies or dangerous moments, the body's stress response can activate fight-or-flight responses can help you react quickly and decisively to protect yourself or others (14).
Age
Memory changes throughout the lifespan. Older adults sometimes find it harder to remember specific details or events from the past, like what they had for breakfast yesterday. However, their general knowledge, like knowing that Rome is the capital of Italy, is fine. Sometimes, older adults might also struggle with working memory, like remembering their grandkid’s phone number or items on their grocery list (15).
Research has shown that as you age, your ability to control certain brain regions involved in memory decreases. Specifically, older adults show weaker connections between different parts of the brain that control memory and attention, which decreases their memory for certain things (16). This suggests that aging not only affects specific memory-related areas but also changes how different parts of the brain work together, potentially leading to difficulties in memory and cognitive control as people age.
How to Enhance Memory
Memory is dynamic and ever-changing. As we saw above, it can be influenced by many factors such as experiences, emotions, environmental stressors, and inevitable things like getting older. At the same time, this process can also work both ways— while environmental factors and emotions can impact and even decrease memory, there are also things you can do to improve your memory.
Actively retrieve information. Next time you’re going to the grocery store, instead of just reading over your grocery list, try rehearsing in your head what you need to buy. You could quiz yourself, use flashcards, or even tell someone else what you need to get. This helps your brain make stronger connections and remember things better.
Stay mentally stimulated. Challenge your brain regularly with activities that promote cognitive health and memory function. Research shows that as people age, they tend to learn less novel information and stay stuck in our same habits. This is bad for the brain because it needs constant stimulation to enhance neuroplasticity and memory functions. Keep your brain busy by solving puzzles, playing brain games, trying new things, or learning new skills.
Get regular exercise. Physical activity has been shown to improve memory by increasing blood flow to the brain, promoting the growth of new neurons, and enhancing connections. Aim for regular exercise, such as walking, biking, or resistance training to keep your brain working at its best.
Get enough sleep. Few things are as important for the brain's ability to form and retain memories as sleep is. During a good night’s sleep, the brain consolidates newly learned information, transferring it from STM to LTM. Additionally, sleep cleans out toxins that accumulate in the brain during waking hours. Aim for 6-8 hours of sleep every night and avoid things that can damage sleep quality like excessive screen time and alcohol.
Takeaways
Memory is perhaps the brain’s most important cognitive function. Memory shapes your identity by allowing you to retain and recall experiences. It also helps you do things without you even having to think about it like driving car or riding a bike. Brain areas like the prefrontal cortex and medial temporal lobe organize memories and help you make decisions. Attention, emotions, stress and getting older are only some of the many factors that can impact memory for better or worse. Finally, doing things like getting quality sleep and practicing active recall are great ways to improve your memory and keep your brain young.
References
William, D. (2006). The half‐second delay: what follows?. Pedagogy, Culture & Society, 14(01), 71-81.
Lieberman, D. A. (2020). Learning and Memory (2nd ed.). Cambridge: Cambridge University Press.
Slotnick, S. D. (2017). Cognitive neuroscience of memory. Cambridge University Press.
Funahashi, S. (2017). Working memory in the prefrontal cortex. Brain sciences, 7(5), 49.
Smith, R., Lane, R. D., Alkozei, A., Bao, J., Smith, C., Sanova, A., ... & Killgore, W. D. (2018). The role of medial prefrontal cortex in the working memory maintenance of one’s own emotional responses. Scientific reports, 8(1), 3460.
Squire, L. R., Stark, C. E., & Clark, R. E. (2004). The medial temporal lobe. Annu. Rev. Neurosci., 27, 279-306.
Chicago
Eichenbaum, H., Yonelinas, A. P., & Ranganath, C. (2007). The medial temporal lobe and recognition memory. Annu. Rev. Neurosci., 30, 123-152.
Roozendaal, B., & McGaugh, J. L. (1996). Amygdaloid nuclei lesions differentially affect glucocorticoid-induced memory enhancement in an inhibitory avoidance task. Neurobiology of learning and memory, 65(1), 1-8.
Roesler, R., Parent, M. B., LaLumiere, R. T., & McIntyre, C. K. (2021). Amygdala-hippocampal interactions in synaptic plasticity and memory formation. Neurobiology of learning and memory, 184, 107490.
Uncapher, M. R., & Rugg, M. D. (2009). Selecting for memory? The influence of selective attention on the mnemonic binding of contextual information. Journal of Neuroscience, 29(25), 8270-8279.
Kensinger, E. A., & Schacter, D. L. (2008). Memory and emotion. Handbook of emotions, 3, 601-617.
Loftus, E. F. (1996). Eyewitness testimony. Harvard University Press.
Manning, C. G., & Loftus, E. F. (1996). Eyewitness testimony and memory distortion. Japanese Psychological Research, 38(1), 5-13.
Lupien, S. J., McEwen, B. S., Gunnar, M. R., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behaviour and cognition. Nature reviews neuroscience, 10(6), 434-445.
Grady, C. L., Springer, M. V., Hongwanishkul, D., McIntosh, A. R., & Winocur, G. (2006). Age-related changes in brain activity across the adult lifespan. Journal of cognitive neuroscience, 18(2), 227-241.
Sambataro, F., Murty, V. P., Callicott, J. H., Tan, H. Y., Das, S., Weinberger, D. R., & Mattay, V. S. (2010). Age-related alterations in default mode network: impact on working memory
