Is it possible to manipulate memory formation and consolidation? And why would we want to do it? Our memories make up so much of who we are, and the things we remember can often define our experience of the world.
And while positive memories can help us grow and thrive, negative memories do not always have such welcome effects. Sometimes, unpleasant memories can be part of a learning curve, getting scalded with boiling water means that next time we will be more careful when handling the kettle.
However, there are also memories that are truly traumatic, and recalling them can lead to distress and serious mental healthconditions, such as post-traumatic stress disorder (PTSD). The study of memory formation, recall, and forgetting attracts a lot of attention and curiosity among neuroscientists, psychologists, and even researchers from the humanities, as there is still so much we do not fully understand about the processes surrounding memory.
And, while we still need to find out more about how memories form in the brain, researchers in recent years have started investigating the possibility of manipulating memories particularly negative ones to see if they can weaken or remove them altogether.
When the brain encodes information, those data become stored in groups of neurons that synapses or links that allow brain cells to “communicate” connect together. Scientists typically associate stronger synapses with a better memory, and the brain constantly “updates” synaptic connections, forming new ones or strengthening old ones, as new memories build or we update older ones.
However, synapses can also become weaker if they are not activated often enough, and the brain often loses some of these connections altogether. Thus, forgetting can occur naturally and, indeed, researchers argue that forgetting is a crucial part of learning and creating new memories.
Forgetting occurs because it would not be energy efficient to indefinitely maintain all the memories that we form each day,” he explained, adding that it “also seems to be a natural consequence of neurogenesis: the process that creates new brain cells in support of future learning. Clearing old and unused memories may be directly related to our ability to learn new things.
But scientists continue to explore the many complications that riddle memory recall and formation. For instance, not all our memories are correct, and sometimes our brains “implement” forgetting as a defense mechanism. Past research has shown that social interactions can influence a person’s memory of an event, as can what other people remember or claim to remember about the same event.
A memory is not simply an image produced by time traveling back to the original event, it can be an image that is somewhat distorted because of the prior times you remembered it. “Memories aren’t static. If you remember something in the context of a new environment and time, or if you are even in a different mood, your memories might integrate the new information.
One way in which forgetting can be adaptive, Berens told MNT, is that, by letting go of irrelevant details, our brains are then better able to recall important information. “[M]y own work suggests that forgetting specific details of an event allows us to focus on the bigger picture and pull out general patterns that can predict the future,” he explained.
“For instance, remembering exactly which trees in the forest bear the most delicious fruit is only useful until you have eaten all of that fruit. Instead of remembering the specifics trees, it may be best to remember the general area of a forest that has the best trees.” This sometimes involves forgetting specific details […] and blurring together many experiences in order to pull out a general pattern. ”
The researcher also noted that another way in which forgetting can be a helpful process is by placing negative memories out of reach so that they are less distressing to the person they affect.
“Memories for emotional or traumatic events lose their emotional tone over time,” said Berens, and “this can help us reappraise and learn from past experience without the need to reexperience all the associated emotions at the same time.” But what happens when traumatic memories persist and resurface unbidden? Experts call this the “intrusive reexperiencing of trauma,” and it is a core feature of PTSD.
Individuals who experience PTSD may spontaneously recall a traumatic memory, or feel as if they are going back into the context that produced the trauma. This effect can cause the person severe distress and lead to erratic behaviors as a coping strategy.
For this reason, some scientists have wondered what approach they could take to weaken or manipulate negative memories and lessen their effect. And, we already know that it is possible to interfere with a memory and stop it from solidifying.
Memories can be actively weakened after formation,“Firstly, there seems to be a time window after memory formation where memories are particularly weak and sensitive to interference — where conflicting information can overwrite the contents of a memory. […] Memories can also be weakened by the simple act of retrieval… Yes, simply recalling a memory makes it more susceptible to being weakened, distorted or erased.”
The drug Propranolol, which doctors can prescribe for PTSD, already goes some way towards weakening distressing memories to dampen their effect. “This is how Propranolol is being used to help patients with PTSD,” he explained, adding that “[f]irst the patient recalls the trauma, which weakens the memory, then the Propranolol is given, which stops the emotions from being re-encoded as a new memory.”
Nevertheless, researchers are still on the lookout for other ways of interfering with memory formation and recall. Such studies could help not only find novel treatments for PTSD and other phenomena such as phobias, but they might also reveal new information about how memory-related brain mechanisms work.
To try and understand whether or not we can artificially manipulate memories, a team of researchers from the Massachusetts Institute of Technology in Cambridge first tried to instil false memories in mice. This initial study, which appeared in Science in 2013, used an optogenetic technique to manipulate the formation of a “hybrid” memory in the mice’s brain. This method requires the use of light beams to activate neurons that researchers have engineered to respond to this stimulus.
In the study, the team led by Prof. Susumu Tonegawa used optogenetic methods to synchronize two groups of neurons, one in the hippocampus, which activated a spatial memory, and one in the amygdala, which activated a fear memory. The experiment was successful, the mice started associating fear with a space where they had never actually had a bad experience.
In their recent experiments, the scientists exposed volunteers to unpleasant content, so that they could first form the unwanted memories. Then, they asked the participants to recall those memories, to trigger the process of memory consolidation. However, at that point, the team administered an anesthetic-propofol to some of the participants. They found that, after this intervention, the volunteers could no longer properly recall the unpleasant content that they had memorized before.
This led the researchers to conclude that sedation could, in some cases at least, help disrupt the reconsolidation of traumatic memories in humans, if delivered as with the earlier study in rats at just the right time. This process could be a helpful method of lessening the impact of traumatic memories in people who are affected by such intrusive thoughts.
“Memories warm you up from the inside. But they also tear you apart,” writes author Haruki Murakami in the novel Kafka on the Shore, and we still have a way to go in learning how best to use our memories for growth, and to stop them from becoming an obstacle.