My earliest memory is from when I was about 4 years old. I was sitting in a stroller and the neighbor's brown Great Dane put his big face right up to mine. I wasn't afraid, but I was in awe of the size of its snout and tongue. I have other memory snippets from this time — an ice cream stand that dished out soft-serve ice cream in little plastic baseball helmets and my grandmother teaching me the proper way to put on the tights that went with my Catholic school uniform. But I don't remember much, if anything, before that. And if you're like most people, you don't either.

Researchers say our average first memory is from about 3 1/2 years old, though that rough estimate varies by culture, according to a 2000 study about cultural memories. Maori New Zealanders, for example, can recall experiences from as early as age 2 1/2 while the Chinese recall events starting around age 4.

But why don't we remember anything earlier than that? The term for this phenomenon is called "infantile amnesia," and it was coined by Sigmund Freud more than 100 years ago. It describes an interesting paradox: Children have enormous learning capacities and soak up information like a sponge, but as adults, we have very few memories of early childhood.

How we remember and forget

Remembering and forgetting Forgetting something? We all are. After we learn new things, our brains throw away half of the new material in an hour. (Photo: Ollyy/Shutterstock)

Two main theories aim to explain why we forget so much of our childhood. The first theory chalks it up to a storage issue — we don't, for whatever reason, have the ability to convert early memories into long-term ones. And the second theory is that it's a retrieval issue — we may have the memory stored somewhere in our brain, but we can't access it. If it's the latter, what causes that retrieval problem? As BrainHQ reports:

One strong possibility is that growing up alters our perception to such a degree that appropriate retrieval cues are never presented. For example, when you were 6 months old, everything in the world probably seemed huge. Your memories of that time are probably colored by towering furniture and lots of talk that you could not yet understand. Accessing these memories might be difficult in the adult world, where tables are no longer three times as big as you are. As we age, our view of the world changes so much that the cues that we associated with our earliest memories are no longer present, so we lose our connection to infant memories.

Some memories last a lifetime: a serious injury, the loss of a loved one, the birth of a child or a wedding. Those are just a few examples, but they all have one thing in common: an emotional connection that, whether positive or negative, helps secure a memory into place. Certain brain structures like the amygdala are specialized for emotional memory, and studies have found that high levels of acute stress may benefit our ability to recall something.

The BBC recently wrote about 19th century German psychologist Hermann Ebbinghaus, who conducted memory experiments on himself to test the limits of memories:

To ensure his mind was a completely blank slate to begin with, he invented the “nonsense syllable” – a made-up word of random letters, such as “kag” or “slans” – and set to work memorizing thousands of them. His forgetting curve charts the disconcertingly rapid decline of our ability to recall the things we’ve learnt: left alone, our brains throw away half of all new material within an hour. By Day 30, we’ve retained about 2 to 3 percent. Crucially, Ebbinghaus discovered that the way we forget is entirely predictable. To find out if babies’ memories are any different, all we have to do is compare the charts. When they did the maths in the 1980s, scientists discovered we recall far fewer memories between birth and the age of six or seven than you would expect.

It's interesting that Ebbinghaus's experiment involved language, as some psychologists have argued that memories can only be created once we've mastered speech. "Language helps provide a structure, or organisation, for our memories, that is a narrative. By creating a story, the experience becomes more organised, and therefore easier to remember over time,” Robyn Fivush, a psychologist at Emory University, told the BBC.

While there seems to be little doubt that language provides our memories with a narrative, it hardly seems like a prerequisite for the ability to form memories. Babies who can't speak, for example, can remember faces, places and things without being able to say the words associated with them. So clearly, there's more to this puzzle.

Can we trust our memories?

Family looking at photo album Even if your memories are based on real events, they may have been reshaped by photos or even stories told by family members. (Photo: wavebreakmedia/Shutterstock)

If you were alive in 2001, you probably remember exactly where you were on Sept. 11 that year. Maybe you even remember watching the terrible events of that day unfold in person or on TV. You may think those memories are as crystal clear in your mind as the blue sky was on that fateful morning. But psychologists say these recollections are surprisingly inaccurate. In fact, a 2003 study of 569 college students found that 73 percent of them believed they saw TV footage of the first plane hitting the north tower of the World Trade Center on Sept. 11, 2001. But that footage actually did not air until the next day.

So what does this mean? Karim Nader, Ph.D., a neuroscientist at McGill University, tells Smithsonian magazine that the very act of remembering can change our memories. Though he admits most of his research has been on rats, he believes it's impossible for humans or any other animal to remember something without altering it in some way.

The very idea that we can't trust our own recollections is unsettling. No one wants to hear that what they hold dear in their mind isn't real. Plus, what could that theory mean for assault victims? Court testimonies? Passing down stories to the next generation? To be fair, not all researchers believe Nader's theory and point to a lack of evidence.

But if you think about it, there's something to Nader's idea. Take, for example, my 8-year-old daughter. She couldn't possibly remember going to "mommy and me" movement classes when she was 18 months old, but I've told her about them, so she knows she went. And she couldn't possibly remember a family trip out of state when she was 2, but she has seen photos from the trip. She talks about both of these things like she remembers them, but all she knows is what her father and I have told her. So even if those "memories" are based on real events, they've been manipulated by the information we provided.

Which leaves us with this thought: Even if we could remember being a baby, would those even be real memories at all?

Angela Nelson ( @bostonangela ) is an exhausted mom of two young daughters and two old cats, and a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide.