What if you could recall forgotten memories?

New research from MIT is shedding light on how our brain forms and recalls memories.


Though Sigmund Freud used his “seduction theory” to describe the phenomenon of repressed memories, such as the trauma of childhood sexual abuse, he later admitted he had not placed proper emphasis on the role of fantasy in the reconstruction of such events. For the most part, using repressed memories as therapeutic tools was abandoned by psychiatrists.

In his book, Fantasyland, Kurt Andersen argues that the sixties brought about a resurgence in many forms of magical thinking, repressed memories included. Two decades later Americans experienced a swell of depressed and anxious clients “remembering” past sexual abuses that never actually happened. The trend in psychiatry was to enable and even foster these fantasies. As Andersen writes:

[The psychiatrists] were devoted not only to believing and confirming the truth of any remarkable story any patient told them but sometimes to helping patients dream up and believe fictional memories.

These extend to “memories” of past lives and other such fictions, another trend active today, often through various forms of hypnosis and suggestion. Yet the process of memory has always confounded us. It is one of the most debated fields in neuroscience. Bit by bit, however, progress is being made. 

We might be highly suggestible animals, yet we also tend to have terrible memories. Some speculate that memory is a cooptation of our ability to predict the future; memory is a form of predicting, only backwards. That’s because all of our experiences become enmeshed in the sticky facet of ourselves we call identity, with more recent experiences influencing older events. 

Japanese Scientist Susumu Tonegawa, MIT’s Picower Professor of Biology and Neuroscience, has greatly advanced our understanding of memory. While his previous focus on immunology won him a Nobel Prize in 1987, his current work on memory is rapidly advancing the field. As Elizabeth Svoboda reports, 

Early this year, [Tonegawa and his team] reported that memory storage and retrieval happen on two different brain circuits, not on the same one as was long thought. His team also showed that memories of an event form at the same time in the brain’s short-term and long-term storage areas, rather than moving to long-term storage later on. Most recently (and tantalizingly), his lab demonstrated what could someday be a way to bring currently irretrievable memories back into conscious awareness.

Beyond trends of suggestibility and fantasy, there are memories we truly cannot recall. This is not uncommon. Beyond the very few of us with perfect memory, most can’t remember what we ate for dinner one month ago. Or one week ago. Some of us, yesterday. 

This is part of energy budgeting. Our concern is tonight’s dinner, not last night’s—we need to predict forward where we’ll secure sustenance, not concern ourselves over what has already come and gone. Yet certain memories might prove useful, like your wife’s name or where you parked the car, which is why Tonegawa’s research is so fascinating. 

Longstanding dogma had it that your experiences were recorded by your hippocampus, which were then sent to engram cells in your prefrontal cortex (PFC) for long-term storage. Sleep is considered an especially important component of memory formation. Researchers speculate that dreams are your brain’s way of interpreting and effectively remixing your experiences into the larger construction of your identity. 

Sleep and dreams aside, Tonegawa showed that both your short-term and long-term memory circuits are simultaneously activated during an experience thanks to a “detour circuit” between the subiculum and the PFC. Engrams in the subiculum recall events in the short term, while in the long-term cortical engrams take over. Eventually, engrams around the hippocampus disappear. Your long-term memories, those over two weeks old, arise from your PFC. 

In October, Tonegawa and team followed up this research with a paper published in PNAS. The authors write,

A combination of immediate early genes, transgenics, and optogenetic techniques has recently provided the long-sought gain-of-function evidence for engram cells in the dentate gyrus of the hippocampus. This evidence has been complemented by loss-of-function evidence in the lateral amygdala.

The group attempted to non-invasively “reawaken” memories in mice. Led by Dheeraj Roy from Tonegawa’s lab, the team mildly shocked mice while suppressing their PAK1 genes, a protein that strengthens the connection of experience and memory. The next day the mice should have been fearful entering the cage, yet they showed no sign of fear—the “loss of function” in their amygdala. 

Amazingly, the application of laser lights switched on this fear response. Though the engrams were silent thanks to the suppression of PAK1, they were still present. Further application of the PAK1 gene caused their fear response to return. The team speculates that therapeutic injections of PAK1 in humans could potentially awaken our own silent memories. As Svoboda writes, 

Reactivating silent engrams could allow people with memory issues — like Alzheimer’s sufferers, soldiers who have survived explosive blasts and concussed athletes in contact sports — to regain memories that have become inaccessible.

However, she writes that Tonegawa is cautious regarding such applications. Previous popular theories—We only use 10 percent of our brains! I was abused as a child and don’t remember!—rely on an ignorant supposition of research, which is then projected broadly. Good science needs verification. 

Still, this avenue of research is exciting. Considering the rising death rate from Alzheimer’s disease, any potential therapeutic applications should be thoroughly studied. Considering even newer research coming from Tonegawa and Roy about how we remember spatial orientation, this MIT lab is helping us understand ourselves better by the day. 

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Derek Beres is the author of Whole Motion: Training Your Brain and Body For Optimal Health. Based in Los Angeles, he is working on a new book about spiritual consumerism. Stay in touch on Facebook and Twitter.

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