Exploring the Functioning of Human Memory

The more you understand your memory, the better you'll be at enhancing it. Here's a basic guide to how your memory operates and how the process of aging impacts your ability to recall information.

Your baby's first cry... the taste of your grandmother's molasses cookies... the smell of a salty ocean breeze. These moments form the mosaic of your life experiences, giving you a sense of identity. They create comfort in familiar faces and places, bridge your past with the present, and shape your view of the future. In essence, our collective memories -- the "memory" that defines us -- is what shapes who we are.

Many people talk about memory as if it were something they possess, like poor eyesight or a thick mane of hair. However, memory isn't a tangible object like a part of the body -- it's a concept that describes the process of recalling information.

Previously, many experts described memory as a small filing cabinet, with individual folders where memories were stored. Others compared it to a neural supercomputer nestled beneath the skull. But today, specialists agree that memory is far more intricate and elusive, existing not in one location but as a widespread process throughout the brain.

Can you recall what you had for breakfast today? If you visualized a plate of fried eggs and bacon, you didn’t pull that image from some forgotten corner of your brain. Instead, your memory was formed by an elaborate reconstructive process -- a unique ability each person has -- that pieced together scattered impressions from different cells across the brain. Your memory is a collective of systems, each playing a distinct role in creating, storing, and retrieving information. When the brain is functioning properly, these systems cooperate seamlessly to form coherent thoughts.

What seems like a single memory is actually a sophisticated creation. Take the image of a pen: your brain recalls its name, shape, function, and the sound it makes when it scratches paper. Each element of this memory is sourced from various regions of the brain. The brain then reconstructs the full image of the pen by pulling together these parts. Neurologists are just beginning to uncover how these components are reassembled into a unified memory.

When you ride a bike, different memories are activated. One set of brain cells stores the memory of how to operate the bike, another recalls the route to the end of the block, a different set holds the safety rules, and another triggers the nervous feeling when a car comes too close. Despite all these distinct processes, you're unaware that each comes from a separate part of your brain because they work in harmony. Experts suggest there’s no clear boundary between how we remember and how we think.

This doesn’t mean that scientists have fully decoded how the memory system operates. They still don’t have a complete understanding of how memories are formed or what happens during recall. The quest to understand how the brain organizes and stores memories, as well as where memories are acquired, has been a continuous challenge for neuroscientists for decades. However, enough has been uncovered to make some informed assumptions. Memory processing begins with encoding, progresses to storage, and finally reaches retrieval.

On the following page, you’ll explore how encoding functions and the brain's activity during memory retrieval.

Memory Encoding

Encoding is the initial phase in memory formation. It’s a biological process rooted in sensory perception. Take, for instance, the memory of the first person you ever fell in love with. When you first encountered them, your visual system likely noted physical attributes, such as their eye and hair color. Your auditory system might have captured the sound of their laughter. You probably detected the fragrance of their perfume or cologne. You may have even felt the touch of their hand. All these distinct sensations were sent to the hippocampus, the part of the brain that integrates these experiences into a unified memory of that particular person.

Experts suggest that the hippocampus, in conjunction with the frontal cortex, plays a crucial role in analyzing sensory inputs and determining their significance for memory retention. If deemed important, these inputs could eventually become part of your long-term memory. As previously mentioned, this information is distributed and stored in various regions of the brain. The exact process by which these fragments are later recognized and retrieved to form a coherent memory remains a mystery.

While memory begins with perception, it is encoded and stored through electrical impulses and chemical signals. Here's how it works: Nerve cells connect with one another at a location known as a synapse. These synapses are the sites where all brain activity takes place, with electrical pulses transmitting messages across the gaps between cells.

When an electrical pulse crosses the synaptic gap, it triggers the release of neurotransmitters. These chemical messengers travel across the space between cells, attaching to neighboring neurons. A single brain cell can form thousands of connections like this, resulting in approximately 100 trillion synapses in the average brain. The structures on brain cells that receive these electrical signals are called dendrites—branch-like extensions that connect with nearby neurons.

The connections between neurons are not fixed; they constantly change. Brain cells collaborate in networks, grouping together to specialize in different types of information processing. As one cell sends signals to another, the synapse between them strengthens. The more signals transmitted, the more robust the connection becomes. With every new experience, the brain subtly reorganizes its physical structure. This plasticity, as scientists term it, allows the brain to rewire itself, even in the case of damage.

As you acquire knowledge and experience, and as changes take place at the synapses and dendrites, new connections form within your brain. In response to your experiences, the brain continuously organizes and reorganizes itself, building memories triggered by external influences like education, training, or life events.

When you practice something repeatedly, these actions strengthen the neural pathways in your brain. For example, if you keep playing a piece of music, the repeated activation of certain brain cells in a specific sequence makes it easier to reproduce the same sequence later. As a result, your performance improves—playing faster, with fewer errors. Keep practicing long enough, and it becomes flawless. However, if you take a long break from practice, your performance may degrade, revealing that the brain has started to forget what was once mastered.

To form a memory, it's crucial that you first pay attention. Since your brain can’t focus on everything all the time, much of what you encounter daily gets ignored, with only a select few stimuli entering your conscious awareness. If you remembered every detail, your memory would be overloaded before your day even begins. What remains unclear is whether the brain filters out stimuli during the sensory intake process or only after it assesses their relevance. What we do know is that the way you focus on information plays a vital role in determining how much of it you remember.

The next page delves into how information is stored in both short-term and long-term memory.

Short and Long Term Memory

Once a memory is formed, it needs to be stored, even if only for a short while. Many experts propose that memories are first stored in the sensory stage, then in short-term memory, and for some, eventually in long-term memory. Since the brain can't retain everything, these stages act as filters, helping us avoid becoming overwhelmed by the constant influx of information we face daily.

A memory begins when we perceive something: The process of registering information during perception takes place in the very brief sensory stage, lasting only a split second. It is your sensory memory that keeps a perception—whether it's a visual image, a sound, or a touch—alive for a fleeting moment after the actual sensory experience has passed.

Following that initial moment, the sensation is stored in short-term memory. This form of memory has limited capacity, typically holding around seven pieces of information for no more than 20 to 30 seconds. However, you can expand this capacity to some extent using memory techniques. For instance, a ten-digit number like 8005840392 may be too much for short-term memory. But when broken down into smaller chunks, like a phone number (800-584-0392), it can remain in your short-term memory long enough to dial. Repeating the number to yourself also helps extend the retention time.

Crucial information is gradually transferred from short-term memory to long-term memory. The more often the information is used or repeated, the higher the likelihood that it will be stored in long-term memory, or 'retained.' (This is why studying enhances test performance.) Unlike sensory and short-term memory, which are temporary and fade quickly, long-term memory can store vast amounts of information indefinitely.

People generally find it easier to remember information related to topics they already know something about. This is because such material holds more meaning, and can be mentally linked to existing knowledge in long-term memory. This explains why a person with an average memory might recall far more about a specific subject than others.

When most people think of 'memory,' they are referring to long-term memory. However, experts believe that information must first pass through sensory and short-term memory stages before it can be stored as long-term memory. To learn how information is retrieved from long-term memory, refer to the next page. We will discuss how memories are recalled, and explore the phenomenon of 'forgetting'—when a memory cannot be retrieved.

Memory Retrieval

When you attempt to recall something, the information is retrieved unconsciously, then brought into your conscious mind when needed. Although many people believe they either have a "bad" or a "good" memory, the reality is that most people are good at remembering some things but struggle with others. If you're having trouble remembering something (and assuming there’s no physical illness involved), it usually isn't due to a flaw in your entire memory system, but rather an issue within a specific part of it.

Let’s examine how you remember where you placed your eyeglasses. At night, when you go to bed, you must register the location of your glasses: You have to pay attention as you set them on the bedside table. Being aware of their position is crucial; otherwise, you won’t remember where they are the next morning. This information is then stored, ready to be retrieved later. If everything works correctly, you'll recall exactly where you left your eyeglasses when you wake up.

If you've forgotten where your eyeglasses are, one of several things might have gone wrong:

To stop misplacing your eyeglasses, you need to ensure that all three stages of the memory process function correctly.

If you've forgotten something, it might be because you didn’t encode it properly, you were distracted during the encoding process, or you’re having difficulty retrieving it. If you can’t remember where you put your eyeglasses, you may not have truly forgotten them—perhaps their location never made it into your memory at all. For example, you might say you recognize a five-dollar bill, but you've likely never encoded its appearance well enough to describe it accurately if asked.

Distractions while trying to remember something can significantly hinder the encoding of memories. For instance, if you’re reading a business report in a bustling airport, you might think you’ve absorbed the information, but it may not have been effectively stored in your memory.

Finally, you might forget something simply because you're having trouble retrieving it. If you’ve ever struggled to recall something at first but later remembered it, it could be because the retrieval cues didn’t match the way the information was encoded in your memory.

As we age, memory difficulties tend to become more prevalent. In the next section, we will explore how aging impacts memory.

Effects of Aging on Memory

Imagine you're at a business event, and you spot a colleague from across the room. As you approach, you suddenly can't recall their name. It's unlikely that you're developing Alzheimer's disease, though many might jump to this conclusion. What you're experiencing is actually a failure in the memory assembly process – a phenomenon that starts in your 20s and worsens as you reach your 50s. This decline related to aging is seen across various animal species, beginning at the point of sexual maturity.

Earlier in this chapter, we discussed how, as you learn, your brain doesn’t fundamentally change its structure, nor does it grow new nerve cells. Instead, the key changes happen in the connections between existing cells. Synapses strengthen, and cells form more robust connections. However, with age, these connections begin to deteriorate, which makes it more difficult to retrieve memories.

Researchers propose various theories to explain this decline, but most agree that aging leads to significant cell loss in a small region at the front of the brain, which results in a reduced production of acetylcholine. This neurotransmitter is crucial for learning and memory.

Certain brain areas, critical for memory, are especially susceptible to aging. For instance, the hippocampus loses 5 percent of its nerve cells every decade, resulting in a 20 percent reduction by the time you reach your 80s. Additionally, the brain itself shrinks and operates less efficiently as you grow older.

Other factors can also accelerate this cognitive decline. You might carry genes that predispose you to these issues, have been exposed to toxins, or perhaps have had habits like smoking or drinking excessively. All of these factors contribute to a faster decline in memory.

As you age, certain changes in the brain can make memory retrieval more challenging. However, this doesn't mean memory loss or dementia are inevitable. While certain cognitive abilities do decrease over time, most people maintain strong memory well into their 70s. Research shows that on many cognitive tests, a 70-year-old can perform as well as a 20-year-old, and people in their 60s and 70s often outshine younger individuals in verbal intelligence.

Research has demonstrated that many memory difficulties encountered by older individuals can be improved or even reversed. Studies involving nursing home residents show that providing challenges and rewards led to notable memory improvements. Moreover, physical activity and mental stimulation can greatly enhance cognitive function.

Animal studies suggest that brain stimulation can prevent the shrinking of cells and may even cause the brain to increase in size. For instance, rats in enriched environments with toys and challenges have larger, healthier brains. Additionally, animals who engage in frequent mental exercises show more dendrites, which are vital for cell communication. Research indicates that as we age, a stimulating environment encourages dendrite growth, whereas a monotonous one hinders it.

It is important to note that as you grow older, you might not learn or remember as quickly as you did in your younger years. However, your ability to learn and recall information will likely remain nearly as strong. In many cases, the decline in cognitive function in older adults is not due to any physical or structural problem, but simply due to underuse of the brain.

ABOUT THE AUTHORS:

Richard C. Mohs, Ph.D. has served as the vice chairman for the Department of Psychiatry at Mount Sinai School of Medicine and the associate chief of staff for research at the Bronx Veterans Affairs Medical Center. He has authored or co-authored over 300 scientific papers and has led many research studies focused on aging, Alzheimer's disease, and cognitive function.

Carol Turkington is an accomplished freelance writer with a focus on health and psychology. She has worked as an editor and writer at both Duke University Medical Center and the American Psychological Association. With over 40 books published, her works include The Memory and Memory Disorders Sourcebook, The Encyclopedia of Memory and Memory Disorders, and The Brain Encyclopedia.