We tend to think of memories like the contents of a museum: static exhibits that we look at to understand the present and prepare for the future.
Recent research, however, suggests that they are like well-thumbed library books that wear and change a little each time they are taken off the shelf.
Think of one of your happiest memories. Indeed. Stay with the memory. Let your mind’s eye wander over the scene. See if you can feel the spark of joy or hope you had in that moment. Let a minute pass. Maybe two.
If you played along with this experiment, you are physically different now than you were a few minutes ago.
When you first remember, your brain cells are awake for a few minutes before they start firing chemically at each other. That action activated the regions of your brain involved in processing emotions, which is why you may have re-experienced some of the emotions you did during the event.
Chemical and electrical signals are transmitted throughout your body. If you were stressed before you started this exercise, your heart rate will likely slow down and stabilize as the levels of cortisol and other stress hormones in your blood decrease. If you’ve been calm, your heart rate may have sped up due to excitement.
Either way, the regions of the brain that light up when you get a reward are full of dopamine.
Memory has changed you. But by recalling this memory, neuroscientist Steve Ramirez says, you’ve also changed the memory.
Other memory elements are increasing in importance. Others retreated. Your mind screamed and entered information without your knowledge. The state you were in at the time of the memory left an emotional fingerprint on the memory, as the neurons activated in your brain are synchronized with those activated by the memory.
Each time you revisit this exciting scene you change it a little bit, both as a physical experience and as a physical network of cells.
Humans have engaged in this two-way task of memory revision for as long as we know it. But over the past two decades, neuroscientists have discovered mind-bending ways to control this process (in rats, at least): inserting false memories, removing real ones, reviving memories thought to have been lost due to brain damage, blocking the memory of an emotional response to one event and attaching it to the memory of another.
“It’s all part of a major shift in science to make memory manipulation commonplace in the lab,” Ramirez wrote. his latest book“How to Change Memory: One of Neuroscience’s Quest to Change the Past” (Princeton University Press). “Memory can change me completely, but I have the power to change it again – with my mind and my science.”
In movies about things like this, there’s often a negative atmosphere surrounding the character of a memory-fixing scientist. Ramirez, a professor at Boston University, is friendly, sincere and keeps a giant inflatable T-rex named Henry in his office.
This research is not seen as the next frontier of forced mind control but as an alternative way to reduce psychological suffering, alongside medication and psychotherapy.
“It’s amazing that we can do these things in modern neuroscience,” Ramirez said recently from his lab in Boston. “But real life, the main purpose of all this is to restore health and well-being to a living thing…. Memory manipulation is another solution. [that] it can become part of our clinical toolkit.”
Memory is the reason Ramirez exists at all.
His father was once kidnapped at gunpoint by the military in his hometown of El Salvador and falsely accused of being a left-wing rebel. (Their “evidence”: He had a beard.) He wasn’t killed when one of his captors took a second look at him and realized he was a generous classmate who used to eat his lunch.
Both of Ramirez’s parents immigrated to the US before he was born, and raised him and his older siblings in Boston. Ramirez received his bachelor’s degree in neuroscience from Boston University in 2010 and his doctorate from MIT in 2017. As a graduate student he joined the lab of Nobel laureate Susumu Tonegawawhere he was paired with a postdoc colleague named Xu Liu.
Both Ramirez and Liu were drawn to memory research as a potential therapeutic tool, and quickly found it as friends and lab partners.
Their first major success together came in 2012.
Three years earlier, a team at the University of Toronto identified neurons that light up when a mouse is exposed to a fearful stimulus – in this case, a sound that was previously associated with shock. The Toronto researchers then injected mice with a toxin that killed those brain cells that light up when they hear sound.
The result: The treated mice no longer showed a fear response when the sound was played. Actually, scientists had erased some memory.
If the memory can be removed from the lab, Ramirez and Liu think, another one can be planted.
In their research, the pair identified brain cells in the hippocampus of the mouse that activate when the animal receives a startling shock. They then removed the mouse from the enclosure where the shock had occurred and placed it in a new box that contained no visual or other sensory cues associated with the memory of its former location. Next, using light pulses milliseconds long, they activate those same brain cells – without the physical shock of the previous stimulus.
The mouse behaved exactly as it did when it was startled, although it was not startled by what had happened.
You can’t talk to a mouse about its memories. The researchers based their conclusions on the animal’s behavior. And this time, that was evident they had opened the memory.
“It just blew everyone away,” said Sheena Josselyn, a University of Toronto neuroscientist who led a 2009 project to erase fear memories. “When you can do those kinds of things in memories, you know you’ve discovered the neural basis of memory.”
In 2013, Ramirez and Liu released a mouse from a box – let’s call it, as Ramirez did in his book, Box A – and noticed the brain cells that were active while exploring the environment.
They then collected it and placed it in a second box, Box B. With minuscule pulses of light, they stimulated the light cells in Box A, causing a memory of that previous location as it explored the new one. At the same time, they shook the mouse.
When they returned the mouse to Box A, the place where it had never been hurt, it froze in fear.
The rat’s negative memory of the shock in Box B was, in effect, reversed from what had been a neutral memory of Box A. The scientists had you have created a false memoryanother seminal feat.
In their final project together, they put a mouse in an enclosure with other mice and observed neurons firing as they responded positively to social interaction.
Then they moved that mouse to a smaller cage than usual, where it was alone.
At first, this mouse-sized mouse dimmed the shape of the mouse.
When given a choice between plain water and sugar, healthy rats chose the latter. But when stressed or depressed, rats show no choice. That’s how Ramirez and Liu’s lonely mouse did at first.
But when the scientists activated the neurons associated with the memory of self-exclusion with other mice, the mouse’s behavior suddenly changed. He eagerly poured sweet water on them. Remembering better times had changed its behavior to resemble that of a healthy mouse.
I the paper was published in 2015 in the prestigious journal Nature. But unlike their shared achievements, this one could not be celebrated together. As the review process continued, Liu died suddenly at the age of 37.
Grief, Ramirez writes, is not so different from memory: “Both endure through all the years of life, change us forever, help us decide what is most important.”
Ramirez, now 37, opened his lab at Boston University in 2017. In the years since then, memory researchers have made remarkable strides: to bring back memories is lost in amnesiaopens memory while suppressing emotions attached to it, to remove emotional reactions in one more memory to attach it to another. Tools now exist to erase all events and associated emotions from a rat’s brain, or to reset memories and all associated emotions.
But there is no expectation in the research community that doctors using lasers will one day reshape the memories of human patients.
First, this experiment is only possible with mice that have been genetically modified to have brain cells that light up when exposed to lasers. Genetically modifying a person in this way, the researchers interviewed for this story say, is neither ethical nor practical.
It’s not necessary either.
“We don’t need to generate technological fears of a digital future in which our memories will be distorted – our memories are already successfully distorted in non-digital ways,” memory scientists Ciara Greene and Gillian Murphy write in “Memory Lane: The Perfectly Imperfect Ways We Remember,” published earlier this year.
Humans are suggestive creatures with extremely responsive memories. Armed with a few leading questions, the researchers found that many people can be used easily in believing that they did or saw something that they did not see. We don’t need lasers to activate our memories, which can be called at will or activated by any number of senses, or to edit their contents, which our brains do all the time without any input from us.
The real goal of research like his, Ramirez said, is to uncover the biological mechanisms of memory and apply that knowledge to non-invasive treatments.
If researchers understand exactly how to find memory in the hippocampus of a mouse with brain damage that has made it inaccessible, for example, that knowledge could be the basis of a drug that helps preserve or strengthen certain types of memory in people with dementia or other mental disorders.
Understanding how an animal’s brain integrates memories and the emotional responses they evoke could lead to better psychological treatments for post-traumatic stress disorder.
The obvious dark side of this line of research is that someone who understands how to increase well-being by manipulating memory can easily use the same knowledge for dangerous purposes.
“The idea of misrepresenting our memories may evoke unpleasant feelings of an old future where relationships are erased, identities are changed, and government forces put thoughts into our heads in a mind-controlling society,” Ramirez wrote in his book. But, he said, any tool that exists can be used to harm or to help, and he would rather make well-intentioned progress than none at all.
“The idea of memory manipulation, to me, makes sense if we have morally bound goals, and that morally bound goal is to restore health and nourish human health,” he said. “Exercise is medicine for the brain, and community enrichment is the medicine [and] a good night’s sleep is the cure. What if altering memories therapeutically could also be the answer? Then we get down to business.”
