Okay, pop quiz: What did you have for lunch yesterday? What about the day before? How about last Tuesday?

You might remember yesterday, but you probably don’t remember last week. And even if you have a guess, you might have some nagging doubts that it was something else. Now think of the most vivid memory you have.

Maybe it was when one of your grandparents passed away. Or when you graduated from high school. Or your first break up.

You probably remember all sorts of details from what happened, like where you were, who you were with, and even the exact words someone said or the clothes you were wearing. Psychologists call these super detailed memories flashbulb memories. They get seared into your brain, and you’re sure you remember everything about your experience, even years afterward, as if it were yesterday.

But even your most vivid memories might not be as reliable as you think they are. I’m Brit Garner, and this is SciShow Psych.

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The term “flashbulb memory” was coined by psychologists Robert Brown and James Kulik in 1977, to describe the vivid memories people have after emotionally intense events. Many of the people Brown and Kulik talked to said the events that caused these memories were upsetting events in the news like the assassinations of President Kennedy or Martin Luther King, Jr.

We don’t know exactly how flashbulb memories form, but based on fMRI brain scans, scientists think two main parts of the brain are involved: the hippocampus, which helps form new memories, and the amygdala, which processes emotions. These memories can be difficult to study because the best way to do a good experiment is after an unexpected, major news event — and researchers can’t really plan for that in advance.

Despite that, we’ve learned a fair amount over the years. We know, for example, that people create flashbulb memories around traumatic events, but they don’t always have to be negative experiences. In 2007, researchers found that both East and West Germans formed flashbulb memories about the fall of the Berlin Wall, regardless of whether they thought it was a good or a bad thing.

We also know that even though these memories are super vivid, they’re not necessarily accurate. That’s probably because people tend to think and talk about vivid memories a lot. Psychologists call this rehearsing a memory, and flashbulb memories can get rehearsed many, many times.

But the rehearsal process isn’t perfect. Your brain will often try to fill gaps in your memory with things that might feel like they’re true, but really aren’t. So if you’re rehearsing a flashbulb memory, and something fits the pattern of the event you’re thinking about, your brain can make it part of the memory without you even realizing.

Studies done on flashbulb memories after 9/11 helped confirm this. Researchers realized that the horrible tragedy probably generated flashbulb memories in a lot of people, so they started doing studies. For example, one group at Duke University quickly gathered 54 volunteers and asked them to describe their experiences on that day.

The participants were also asked to describe another, more ordinary event that had happened a couple days before. Then, the researchers brought the participants back either 1, 6, or 32 weeks later and asked them to recall both memories. Their descriptions of the ordinary events got less accurate over time, which wasn’t surprising.

When asked, the volunteers all said that the much-more-vivid 9/11 memory would be more consistent. But here’s the thing: the subjects’ memories of what they did on 9/11 were just as inconsistent as the ordinary memories from the same time. People felt like they remembered vivid details from 9/11, but those details were different from what they told to the researchers right after it happened. In fact, 42% of the inconsistencies in both kinds of memories came from the distinctive details the subjects thought were true.

In another, larger study, 2,000 people were surveyed about their memories of finding out about the terrorist attacks on 9/11. They responded to surveys one week, 1 year, 3 years, and 10 years after the attacks, and their memories of the details became less consistent over time.

On average, by the time people took the survey 3 years after the the attacks, they only remembered 57% of the details accurately, even though they were sure they were remembering right. 10 years after the attacks, the accuracy was about the same — so people’s memories got less accurate at first, but then stabilized.

So what does this mean for your flashbulb memories? Well, not everything in a flashbulb memory is completely wrong. The basics of what happened are probably accurate. But the vivid details that make it feel so fresh – those are a lot less trustworthy. Even if they feel like they happened yesterday, your flashbulb memories aren’t perfect.

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