Brains, lasers, and memories: oh my!

Science is always cool. But sometimes, it’s cool enough to be mentioned in the New York Times, CNN, BBC, and every major news outlet. It takes a very special experiment to make that happen – combining sexy research methods with science fiction like applications. This is one of those papers.

Ramirez and Liu et al. (2013). Creating a False Memory in the Hippocampus. Science; doi:10.1126/science.1239073.

(hidden behind paywall. Click here for the co-authors’ TED talk).

When I read the abstract of this article, I was excited. Creating false memories? By shooting lasers at brains? We’re already doing that? FANTASTIC! When I read through the full article, I was amazed at the technical skills involved in the research – they used everything but the kitchen sink to make this project work. But the most remarkable aspect for me is its implications for our day to day understanding of our own memories and minds.

At its most basic, the authors of this paper labelled the ensemble of neurons involved in a specific memory (called an engram) with a laser-activated switch, then simultaneously activated that engram while creating a new memory, kneading the two into one completely one artificial memory.


To understand why this happened, it’s necessary to understand how memory, in general, works at a synaptic and systems level. A memory, like any thought or feeling, is a physical thing at the cellular level, contained within a distributed collection of neurons that more-or-less mimic what happened when that memory was created. This means that a memory, any memory, is a collection of cells activating together. If you consider each neuron involved in a memory as a point, with their connections to each other as lines, then a memory can be thought of as a sort of living polygon; a constellation of cells in the brain that activate in a particular pattern and a particular rate and recreate a past experience.

However, these shapes are far from static. They stretch, shrink, or simply break. This happens because of the brain’s plasticity – it’s constantly changing microstructures. There’s a phrase taught in every basic class on the brain:  neurons that fire together, wire together. It means that when two neurons are activated at the same time, they begin to facilitate one another’s activation, so that in the future, if one is firing, it’s easier for the other to fire as well. If you think about it in terms of Pavlov’s dog, the firing neurons underlying the hearing of the bell became “wired” with the neurons underlying the salivation.

When a memory is recalled, the neurons underlying that memory are activated. But those are far from the only neurons active in the brain. Other neurons also firing become slightly wired with the neurons of that memory. This has the effect of changing the memory, ever so slightly. But over time, this effect is strong enough to significantly alter a memory.

This is the reason that cognitive-behavioral therapy works, why eyewitnesses are frighteningly inaccurate, and why this study was possible.


First, the researchers put the mice in a box (Box A) it had never been before. As the mice explored the box, the cells underlying this memory were implanted with a light-activated switch (via expression of channelrhodopsin linked to the c-fos gene).  This switch allows researchers to turn on these neurons by shining a blue light at it (this super trendy technique being called optogenetics). A day later, they were put into were put into another new and different box (Box B). After briefly exploring the box, two researchers did two things simultaneously to the mice:  activate the neurons from the previous day’s memory and deliver an electrical shock to the mice’s feet.

On the third day, the mice were put back into Box A, where they displayed fear behavior, despite never having been shocked in this box. By artificially activating a memory and delivering a shock, the two experiences got paired together. For lack of a better word, a false memory was created. Immediately after recalling the false memory, the activity in the mice’s amygdala, a fear processing center, matched the behavior of recalling a genuine fear memory.

Moreover, the false memory complicated the genuine memory of Box B. The mice displayed fear behavior when put back into Box B, but not as much as mice in Box B who did not have the memory of Box A activated when receiving the shock.


So is this really, truly a “false memory?” When the memory of Box A was activated and the shock was delivered, was the mouse re-experiencing Box A, like being lost in a daydream? Or was it not even aware that it’s memory of Box A was open?

Unfortunately, the experiment can’t the questions of the mice’s cognition. The minor crossover of fear behavior in Box B tells that in some way, the mice were aware of being shocked while in Box B, but more strongly associated the shock with the artificially activated memory of Box A.

For me, this research paradoxically amazed and underwhelmed me. It amazed me with the technical difficulty involved in the work and at the elegant simplicity of the experiment, but at the same time, it was a very obvious experiment. The researchers were attempting a proof of concept:  that memories can not only be activated artificially but tampered with.

In the course of our natural lives, this is something we do everyday. We think about something while interacting with reality, and those two worlds – inner and outer – collide in neural networks. When this is done intentionally and with the guidance of a professional, it is called therapy.

The media has overhyped the implications of this article. It’s not Eternal Sunshine of the Spotless Mind. It’s not Inception. It’s forced learning. Without the insight into the experiential aspect of artificially stimulating a memory, it’s premature to discuss any moral implications memory tampering holds. Because like “genetically modified” foods, what is being done with science is merely an elaboration of what happens naturally.

This research will be remembered as a milestone in learning and memory, and the authors are well-deserving of many high accolades. But it’s important to remember that this groundbreaking research is a very rough approximation of what happens naturally every day in our lives. We’re constantly editing our own memories – not just of the boxes we’ve explored but of our whole lives. Being aware of how we remember ourselves is a thought that should be incepted into everyone’s mind.


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