How memory works & keeping it sharp

You probably remember what you had for lunch without trying. Learning something new, like a recipe or a name, usually takes effort and attention.

Information that means something to you is easier to take in. Thinking about what a word or idea means works better than just noticing how it looks or sounds.

Short-term memory holds a small amount for about 15 to 30 seconds. Newer research suggests it holds about 4 items at once, give or take one.

Repeating information, or working with it, helps move it into long-term memory.

Scientists believe long-term memory can hold an almost unlimited amount. Memories are linked together in networks of related ideas.

New memories take time to settle. At the level of brain cells this takes a few hours, and across the wider brain it can take weeks or longer.

Recall is pulling something up with no hints, like an exam answer. Recognition is knowing it when you see it, like a face. Relearning is learning something faster the second time.

Your first day at a new job or a birthday dinner are episodic memories. You can usually picture where you were.

The hippocampus, deep in the brain, helps turn new experiences and facts into lasting memories. It also helps you remember places and find your way.

Knowing that Paris is in France, or what a word means, is semantic memory. You often don’t remember when or where you learned it.

The front of the brain (the prefrontal cortex) seems to be busy when we think about meaning.

These memories work without you thinking about them. They show up in what you do rather than in words.

The cerebellum, at the back of the brain, helps with these skill memories, like how to play the piano.

The amygdala, which helps process emotions like fear, helps lock in memories of emotional events. That’s why we often remember emotional moments better than ordinary ones.

Even very vivid memories of big events can contain mistakes. Memory is rebuilt each time, not replayed like a video.

Psychologists call this transience. Access to a memory weakens over time, especially if you rarely think about it.

Absentmindedness happens when your attention is somewhere else. If you set your keys down while thinking about work, your brain may never store where they went.

Most people can’t draw the front of a coin they see every day, because they only take in enough to tell it apart from other coins.

This is called blocking. The information is stored, but you can’t get to it in the moment. It often pops up later when you stop trying.

Old information can block new information, like writing last year’s date in January. New information can also make older memories harder to reach.

In a well-known study, people who were asked how fast cars “smashed” into each other gave higher speed estimates than people asked about cars that “contacted.” A week later, the “smashed” group was more than twice as likely to remember broken glass that was never there.

Our current beliefs and feelings can also color how we remember the past. None of this means a person is lying. It is how all human memory works.

Common, typical changes

• Getting confused about the day of the week but figuring it out later
• Making a bad decision once in a while
• Misplacing things from time to time and retracing your steps to find them
• Sometimes forgetting names or appointments, but remembering them later
• Sometimes having trouble finding the right word

Changes to get checked

• Asking the same questions over and over
• Becoming confused about time, people and places
• Getting lost in places you know well
• Having trouble following directions or instructions
• Struggling with everyday things like driving, shopping or paying bills

Some memory problems have treatable causes, such as low vitamin B12, heavy long-term drinking, or tumors, infections or blood clots in the brain. Side effects from things you take can also play a part, so bring a full list to your clinical provider.

Depression can also make it hard to concentrate, remember details and make decisions.

People with MCI have more memory or thinking changes than usual for their age, but they can still manage daily life. About 12 to 18% of people age 60 or older have MCI.

About 10 to 15% of people with MCI develop dementia each year. Others stay stable, and some return to normal thinking.

Over a century of research shows that sleep helps us keep memories. During deep sleep, the brain replays new memories and moves them into long-term storage.

The waking brain is best at taking in new information. The sleeping brain is best at saving it.

Long exposure to stress hormones, at any age, affects brain areas involved in thinking and memory. The effects depend on when the stress happens and how long it lasts.

Stress can also make us remember stressful events strongly, while making it harder to focus on everything else.

Trouble concentrating, remembering details and making decisions are common with depression.

In a Stanford study, people who often used many media at once were more easily distracted by things that didn’t matter, and were slower to switch between tasks.

Because memories start with attention, doing one thing at a time can help you remember it.

In a trial with 120 older adults, a year of walking-based exercise grew the hippocampus by about 2% and improved memory. That roughly reversed one to two years of normal age-related shrinking.

In one study, students who tested themselves remembered much more a week later than students who simply re-read, even though re-reading made them feel more confident.

Ways to try it

• Cover your notes and say what you remember
• Explain it to a friend
• Use flashcards and keep practicing the ones you miss
• Write down what you learned at the end of the day

Spreading practice over time is one of the most effective learning methods researchers have tested. Cramming may help for a few hours, but it fades fast.

Connecting new information to what you already know helps it stick. Putting it in your own words and relating it to your life helps too.

Grouping information into chunks lets short-term memory hold more. Phone numbers are split into parts for exactly this reason.

Memory tricks (mnemonics) organize information so it’s easier to recall. Examples include acronyms (HOMES for the Great Lakes), silly sentences, songs, and unusual mental pictures.

Saying words out loud also makes them more distinct and easier to remember.

Because forgetting where things are often comes from not paying attention, a fixed spot means you don’t have to remember at all.

Ideas

• A daily to-do list
• A notebook or app for things you want to remember
• A wall calendar for appointments
• Phone alarms for important tasks

Memories start with attention. When you need to remember something, pause, look, and say it in your head or out loud.

Learning new skills, staying physically active, and staying socially connected are all linked with healthy thinking in older age.

Sleep helps the brain organize and store new information. A good night’s sleep after learning can help it stick.

Making a memory is a building process, and recalling it is a rebuilding process. Details can shift or be added without anyone meaning to.

Forgetting a name and remembering it later, or misplacing your glasses now and then, is typical. What matters is whether memory changes get in the way of everyday life.

With enough time, healthy older people can do as well as younger people on many memory and learning tasks.

Re-reading and highlighting were rated as low-value study methods in a major review. Practice testing and spacing out practice were rated as the most useful.

Low vitamin B12, infections, heavy drinking and other health issues can affect memory and may improve with care. Some people with MCI stay stable or return to normal.