In the 2004 romantic comedy Eternal Sunshine of the Spotless Mind, Jim Carrey and Kate Winslet play Joel and Clementine, a recently separated couple who have their memories of each other erased. The procedure is carried out by technicians at a company called Lacuna, Inc., who use Joel and Clementine’s personal belongings to “map” their memories of the relationship, before removing every trace of it from their brains. Although erasing specific memories in this way is not thought possible, recent advances in neuroscience allow memory to be modified in various ways. Researchers discussed ethical implications of manipulating memories in a symposium at the BNA Festival of Neuroscience in London earlier this month.
Barry Everitt of the University of Cambridge described how memories can be modified. It’s widely believed that memories are formed by the strengthening of connections between nerve cells, and then consolidated by reactivation of the neural networks that encode them. Stored memories were once thought to be relatively stable over time. About 10 years ago, however, researchers discovered another memory process, called reconsolidation. When a memory is reactivated (recalled to conscious thought), it is eventually strengthened, but immediately upon recall, it is briefly unstable, thus offering a window for manipulating it.
“Reconsolidation was an heretical issue when it appeared, because it didn’t fit with the notion that consolidated memories persist in the brain forever,” said Everitt. “The notion has instead become that a stable memory becomes destabilized when it is retrieved, and then re-stabilized in the brain. You can block that restablization process to lead to memory erasure.”
For example, lab rats can be taught to fear a specific sound by pairing it with mild electric shocks. After repeated tone-shock pairings, they learn to associate the sound with the shocks, so that even when they hear the tone alone they exhibit fearful behaviors. But if the rats are given a protein synthesis inhibitor just before they hear the sound again, the process is blocked; reconsolidation depends on protein synthesis at synapses. The associative memory is abolished, and the animal no longer fears the sound. On the other hand, enhancing reconsolidation can strengthen the memory, making the rats act more fearful of the tone.
Memory reconsolidation can also be interfered with in humans, raising the possibility of treating conditions such as post-traumatic stress disorder (PTSD). To this end, researchers at McGill University in Montreal published preliminary data suggesting that a drug called propranolol, which lowers blood pressure but also disrupts reconsolidation by virtue of its mode of action, does indeed diminish the emotional aspect of traumatic memories in people with PTSD. The same group of researchers is conducting a randomized controlled trial evaluating the efficacy of the drug, and a similar trial is also under way at Yale.
“They got the subjects to re-tell their traumatic memories under treatment with propranolol,” explained Everitt, while measuring physiological repsonses such as heart rate, which change during stressful situations. When the subjects returned later to do it again, their responses were lessened. “This still needs to be tested properly, but it suggests that it may be possible to diminish the intrusive nature of their traumatic memories.”
“This does not mean that people will forget they experienced a traumatic event,” he added.
The approach might also work to treat addiction. Drug use is a ritualistic activity, and the paraphernalia associated with it can induce cravings and lead ex-addicts to relapse. Everitt and his colleagues have shown that blocking reconsolidation of drug-associated memories reduces self-administration of alcohol and cocaine in mice. And last year, Chinese researchers reported that manipulating reconsolidation to alter memories of drug use can reduce heroin addicts’ cravings for long periods of time.
“Our ultimate goal is to improve the human condition, and it’s astounding that we can manipulate memory in the lab,” says neuroethicist and Dana Alliance member Judy Illes of the University of British Columbia in Vancouver. “We could reduce the suffering of people with PTSD, survivors of war, or rape victims, and this can only be a good thing, but manipulating memory has some disturbing implications, so I think we need to be very cautious about exactly what it is we’re doing.”
Memories are integral to our everyday lives, and we draw on our past experiences to guide our present behaviors and decisions. Yet, despite advances in our understanding of the cellular basis of memory, we still know very little about how networks of neurons encode complex memories like the ones we have for life events, or how the neural traces for different memories are related to one another. [See: Probing the Workings of Human Brain Cells]
“Memory is an extremely complex phenomenon and we’d be complicating it even further,” says Illes. If we could erase specific memories, or just dampen the emotional responses to them, can we be sure that this would not precipitate some kind of butterfly effect on related or overlapping memories?
Memory is also integral to our sense of self-identity. It is a mental diary of the events that we experience, which gives us continuity as individuals across our lifespan. We hold some memories dear in our hearts; others may be recollected with less fondness; and yet others may be upsetting or even traumatic. Collectively, though, the contents of our mental diary make us who we are, and by manipulating them we may risk losing a part of the historical narrative that we value.
Some ethicists argue that we should be free to manipulate our memories if we wish, in order to enhance our well-being, but Illes suggests the implications of doing so may stretch far wider, and could have a detrimental effect on the collective memories bind people together. “What would happen to stories about the Holocaust, or about the genocide in Rwanda, or the civil war in Syria? Would future generations still be able to understand what happened to their ancestors?”
The symposium was sponsored by the European Dana Alliance for the Brain and the International Neuroethics Society.