Everyone has an earliest memory —— clearly one of our memories must be the oldest. And, barring a belief in past lives, this memory must be of an event that happened within a knowable time frame —— some time between now and when our minds first came into existence. But how can we discern whether the earliest memory we think we have is an accurate representation of something that happened?

When people claim to be able to remember the mobile that hung above their beds when they were a baby, or the hospital room in which they were born, or the warmth they felt inside their mother’s womb, they are recalling what psychologists refer to as impossible memories. Research has long established that as adults we cannot accurately retrieve memories from our infancy and early childhood. To put it simply, the brains of babies are not yet physiologically capable of forming and storing long-term memories. And yet many people seem to have such memories anyway, and are often convinced that they are accurate because they can see no other plausible origin for these recollections.

But actually, it does not take much to think of a few alternative explanations. Is there really no other way we could know what our mobile or crib looked like, or that we got caught in the latch of our crib, or that we had a musical bear? Surely there could be external sources for this information: perhaps old photographs or a parent’s retelling of events. We might even have memories of objects of personal importance because they were still around much later in our lives.

So we know that at least some of the necessary raw material to build a convincing picture of our earlier childhood can be found elsewhere. When we then place this information into seemingly appropriate contexts, such as a retelling of an early life event, we can unintentionally fill in our memory gaps, and make up details. Our brains piece together information fragments in ways that make sense to us and which can therefore feel like real memories. This is not a conscious decision by the ‘rememberer’, rather something that happens automatically. Two of the main processes during which this occurs are known as confabulation and source confusion.

As Louis Nahum and his cognitive neuroscience colleagues at the University of Geneva put it, ‘Confabulation denotes the emergence of memories of experiences and events which never took place.’ This single word describes a complex phenomenon that affects many of our memories, particularly early ones. Of course, in the case of early childhood memories, this definition can fall a bit short: the event may have actually taken place, it is just impossible that our brains were able to store this information at such a young age and present it back to us in a single meaningful memory later on.

Alternatively, the belief that we have early childhood memories of events like birth may be simply due to misidentifying the sources of information. This is known as source confusion —— forgetting the source of information and misattributing it to our own memory or experience. Wanting to remember our lovely childhoods, we may mistake our mother’s stories for our memories. Or we may meld into our personal narratives recollections told to us by our siblings and friends. Or we may mistake our imagination of what our childhood could have been like for a real memory of what it was like. Of course, memory errors can also be due to confabulation and source confusion working in tandem.

One of the first experiments which demonstrated that we can fiddle with our memories of childhood was conducted by memory scientists Ira Hyman and Joel Pentland at Western Washington University in 1995. Their 65 adult participants were told that they were taking part in an experiment investigating how well people could remember early childhood experiences. They were told they would be questioned about a number of events which they had experienced before the age of six, details of which had already been provided by their parents through a questionnaire. Finally, they were told that accuracy of recall was paramount.

But of course this was no regular childhood memory study. The researchers did not just want to see how well the participants remembered true events —— they wanted to see how well they remembered events that had never actually happened. Among the true accounts obtained from the participant’s parents they had hidden a false account they had made up themselves: ‘When you were five you were at the wedding reception of some friends of the family and you were running around with some other kids, when you bumped into the table holding the punchbowl and spilled the punchbowl on the parents of the bride.’ Appropriately, the study is frequently known simply as the ‘spilling the punchbowl’ experiment.

It is easy to picture this event —— it’s both emotional and plausible. We all know what weddings look like in our particular cultures and countries. We all know what a punchbowl looks like, or at least what it might look like. We all know that weddings are generally formal events, so we likely picture the parents of the bride as an older couple dressed up for the occasion. It is easy to picture ourselves running around in this situation at the age of five. And, as it turns out, it is even easier to picture all this if we imagine the event happening for a few minutes.

Each participant was asked first about two true events which the researchers had learned about from the participants’ parents, and then they were asked about the fake punchbowl incident. After giving participants basic information for each memory, the researchers asked them to try to form a vivid mental image of the event in order to access the memory. They asked them to close their eyes and imagine the event, including trying to picture what the objects, people and locations looked like. The researchers had the participants come back three times, each visit a week apart, and repeat the process.

What they found will astonish you. Just by repeatedly imagining the event happening, and saying out loud what they were picturing, 25 per cent of participants ended up being classified as having clear false memories of the event. A further 12.5 per cent could elaborate on the information that the experimenters provided, but claimed that they could not remember actually spilling the punch, and were therefore classified as partial rememberers. This means that a large number of people who pictured the event happening thought that it actually did happen after just three short imagination exercises, and that they could remember exactly how it happened. This demonstrates that we can misattribute the source of our childhood memories, thinking that something we imagined actually happened, internalising information that someone suggested to us and spinning it into a part of our personal past. It is an extreme form of confabulation that can be induced by someone else by engaging your imagination.