Take a moment to remember an event that you experienced as a child. Pick something that's important to you - an event that really shaped for the better the person you are today. Now ask yourself: are you sure this event truly happened?

Suppose, for example, that some well-intentioned person could have deliberately planted a vivid false memory of this fictional event in your consciousness, believing that the memory would change you in ways that would benefit your life. How would you feel to discover that this was the case? Perhaps you'd be touched that someone cared so much about your wellbeing that they would give you such a personal and life-changing 'gift'? Or maybe outraged, that this person had brainwashed you without your consent?

The scenario sounds like a plot from a science fiction novel, but it's not necessarily as implausible - at least in principle - as it might seem. For a start, memory researchers have known for decades that our recollections of the past are often inaccurate, and that sometimes we remember entire events that never happened at all. These false memories can occur spontaneously, but they are especially likely to occur when someone plants the seed of a false suggestion in our mind, a seed that grows into a more and more detailed recollection each time we think about it.

Importantly, just like memories of events that truly happened, we know that even false memories can influence how we behave. In one experiment that demonstrates this point, a group of research participants were told that their responses to numerous questionnaires had been fed into a clever computer algorithm, which could predict the likelihood of various childhood experiences. Apparently based on their results, the participants were falsely informed that during their childhoods they became sick from eating spoiled peach yoghurt. A second group of adults did not hear this false suggestion.

Two weeks later, both groups completed a taste test, sampling various foods as part of what seemed to be an unrelated study. The researchers found that both groups ate similar amounts of most of the foods, yet those people who had received the false suggestion ate about 25% less peach yoghurt than the others. The avoidance of peach yoghurt was most pronounced among those people who now said they could 'remember' the fictional sickly incident. In short, it isn't too far-fetched in principle that somebody could deliberately give you a false memory, nor that the right kinds of false memory could have positive effects on your life. Inspired by several studies like the peach yoghurt experiment, some commentators have even imagined taking the idea one step further by inventing the "False Memory Diet."

Could planting 'beneficial' false memories be the next big thing for tackling obesity, or myriad other health complaints from fear of the dentist to depression? Even if such an intervention is scientifically plausible, there still remains the fundamental question of whether it could ever be ethically justifiable.

Certainly, it would be naïve to say that nobody would ever try it. In fact, even looking back several decades, we can find documented cases in which therapists claimed to have tackled their clients' psychological troubles by manipulating their memories. Asking ourselves whether this kind of intervention is justifiable, then, is important: not only because we can conceive of a future in which false-memory interventions are on the menu, but also because in at least some rare cases, practitioners have been ordering from that menu for years.

In new research funded by the Wellcome Trust, and published in the journal Applied Cognitive Psychology, we described a fictional 'false memory therapy' to almost one thousand members of the public from the UK and the USA. These participants were asked to imagine the case of an obese client seeking professional support for weight loss. Without this client's knowledge, the therapist would attempt to plant false childhood events in the client's memory - events designed to change the client's unhealthy relationship with fatty foods. The therapist, however, would only reveal their deception many months after the therapy was complete. Our question for participants was: Would this fictional therapy be acceptable?

Many people are quite open in principle to the idea of deliberately manipulating memories, if doing so could benefit the patient

Remarkably, there was very little consensus on the answer. In fact, whereas 41% of respondents said it would generally be unacceptable for a therapist to treat them in this way if they were obese, 48% said that it would be acceptable. And whereas just over a quarter of people said that the therapy would be completely unethical, these people would be horrified to know that one in ten believed it completely ethical. Many people, it appears, are quite open in principle to the idea of deliberately manipulating memories, if doing so could benefit the patient.

These are striking findings, but they mirror those from a 2011 study examining people's attitudes to so-called "memory dampening" drugs. In that study, just over half of people said that if they were the victim of a major trauma, they would want the option of receiving a drug that would weaken their traumatic memory. And in a separate Pew poll published this July, 23% of American adults said it would be morally acceptable to surgically implant devices in healthy people's brains to improve their cognitive abilities. Incidentally, rather more of the respondents, 34% in total, said they would want such a device in their own brains.

So why are so many of us repulsed by the thought of having beneficial false memories planted in our minds, while so many others are positively enthusiastic about the prospect? To delve deeper, we asked 200 of our participants to elaborate on their reactions to the fictional 'false memory therapy.' For those who found the therapy appealing, the lure of helping people to improve their health was far more important than any other qualms they might have. Some even wished they could receive such a treatment themselves, or provide it for their loved ones. For many of these people, the potential drawbacks of 'false memory therapy' seemed no worse than certain existing health interventions. One American man wrote:

I do not see it as a problem… After all, many medical treatments involve taking drugs or having surgical operations. These involve putting real things into the body. Sometimes they do not turn out beneficial and may even result in more harm than good. So, just putting false thoughts into someone's thoughts (sic) does not seem nearly as invasive or potentially harmful.

Some participants foresaw "mission creep", with the intervention eventually being used for nefarious purposes.

In contrast, many people found the fictional therapy unappealing and sinister, to say the least. Their reasons were more varied. Some were principally troubled by the mechanics of the therapy, pointing out that the notion of health professionals lying to their patients is hugely unethical. Others foresaw "mission creep", with the intervention eventually being used for nefarious purposes. As one British woman wrote:

Far too dangerous.  The first application I can see would be to persuade gay people they "ought" to be heterosexual.  How long before the ruling party used it to "cure" people who voted for the opposition?  That may seem far-fetched now but it may not if they actually had the power.

But for many people, the most unsettling idea was that planting false memories would rob us of our free will and authenticity - our personalities would no longer be genuine, our life decisions no longer truly ours. That's no doubt a perspective with which we all can empathise, one that exposes both the intimacy of our relationship with memory, and the great value we place upon being able to trust it. After all, even those of us who study other people's memory errors can still find ourselves hopelessly addicted to the misbelief that our own memories can be trusted just fine.

Somehow, I can't foresee us ever truly endorsing the planting of false memories for widespread therapeutic use, but who knows what the future may hold? If memory-modifying treatments are possible, and if a substantial chunk of the population find the idea of planting memories strongly appealing, then we may need to ask ourselves important questions about the kind of relationship we wish to have with our memories.

Even if the day never arrives when your family doctor can prescribe a course of false memories, reflecting on this ethical minefield may remind us that recollections are among our most precious assets. Maybe false memories can be just as precious.

Robert Nash is a psychologist at Aston University, UK. He Tweets as @DrRobNash.

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