How extreme fear shapes what we remember.

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Many of us will experience a significant trauma in our lives, says Lesley Evans Ogden. Yet could there be ways to avoid reliving the memories?

It was no ordinary honeymoon. After boarding their flight in Canada on the evening of 23 August 2001, newlyweds Margaret McKinnon and her husband were heading for Lisbon, Portugal. As Air Transat flight 236 soared over the mid-Atlantic, McKinnon went to the lavatory. Nothing inside it was working. “It seemed odd,” she says, but she didn't think a lot of it.

The fear system has evolved to keep us alive — Karim Nader, McGill University

Returning to her seat, the crew served breakfast, but then announced that they would be making an emergency landing. She remembers thinking it seemed early to be arriving in Lisbon. “I didn't really understand at the time what that meant,” she says. She soon found out. Crew instructed passengers to put on their life jackets. The lights flickered, then extinguished. The cabin depressurised. Oxygen masks deployed.
The plane’s systems had shut down after a catastrophic leakage of fuel. “They were shouting that we would be ditching into the ocean,” McKinnon recalls.

After a half hour of preparing for the worst, McKinnon recalls somebody yelling that they’d made it to land. It was the Azores, an isolated archipelago some 850 miles (1,360km) off the Portuguese coast. The pilots had established contact with Lajes, a joint military-civilian air base. Following a harrowing 360 degree spin and several sharp turns to reduce altitude, the crew shouted “brace, brace, brace” as the officers brought the plane to a bumpy landing. Fires licked across the plane’s wheels.

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The stunned passengers and crew descended escape slides and ran across a field to a safe distance, towards American soldiers with guns. Two serious and 16 minor injuries were sustained during evacuation down the chutes, but all 293 passengers and 13 crew survived.
But for many the flight didn’t end there. For some – including McKinnon – the terrifying experience replayed vividly as intrusive memories and nightmares in the months that followed.
The experience inspired McKinnon, now a clinical psychologist, to study what trauma does to the brain – how it changes what we remember and why some people experience Post Traumatic Stress Disorder (PTSD). In recent years, she and a number of other researchers have been trying to understand what makes fearful experiences seem to become imprinted so deeply in our brains. And if they can understand why trauma has such a profound and lasting effect on us, perhaps they can find ways to help people cope better with the aftermath.
Fearful imprint
The link between fear and memory has intrigued researchers and clinicians for decades. Yet the data is conflicting. “Some studies have found that during the recollection of traumatic events, recollection is enhanced. It's very vivid, people recall many details, and people don't seem to have difficulty remembering,” says McKinnon. Other studies have found that recollection of traumatic events can be very impoverished and fragmented, with “a detail here, a detail there, that don't really fit together”, she explains.

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Few studies have looked at memory during the experience of trauma itself, especially for a single, shared event. So McKinnon decided to delve into the memories of her fellow passengers on Air Transat flight 236.
“We wanted to take this opportunity to look at a very ‘controlled’ circumstance, so to speak,” says McKinnon, suppressing an awkward laugh at using “controlled” to describe AT 236’s emergency descent. McKinnon and collaborators examined the memories for 15 passengers on the flight, comparing their recollection of three events: the flight itself, an emotionally neutral event from the same year, and their experience during 9/11, the following month. Six of those interviewed exhibited PTSD symptoms.
The researchers guided subjects’ memories by saying “tell me everything you can remember about the event”, and then further aided retrieval with cues like “what were you thinking, what were you feeling, and what was the lighting like in the cabin?” These detailed recollections were compared with the known sequence of events, and a control group who had suffered less traumatic memories.
What they found was that all passengers, regardless of whether they went on to develop PTSD, had vivid and enhanced recollections of the incident, supporting the idea that fear changes how the brain stores memories. In those that subsequently developed PTSD, “they showed a lot of recollection of extraneous details, not only of the traumatic event, but also for the events of September 11, as well as from the neutral memory from the same time period”, says McKinnon. It suggests that these individuals have difficulty editing what they recollect, or fading the contents of memory.
McKinnon admits that her study represents a small sample, and is cautious about generalising the results, but they are nevertheless intriguing. “Understandably, people were reluctant to participate,” says McKinnon. “And we are very, very grateful to the people who did participate, because it can be difficult to talk about these kinds of things.”

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So if traumatic memories are more vivid, what’s going on inside our heads when they are ‘made’? There are multiple memory systems in the brain. We have physical memories, like how we learn to ride a bike. We have auditory memories for singing songs. And we have more specific “declarative” memory systems heavily involving the hippocampus. The hippocampus stores memory for things like where we parked our car, and that two plus two is four.
But fear activates a different system: our body’s emergency control centre – the amygdala. The amygdala, a pair of almond-shaped structures on the left and right of the brain’s medial temporal lobe, is particularly involved in emotional memories like fear, but also in pleasurable memories associated with food, sex, or recreational drug use. When a memory is particularly striking and unexpected, it activates this emotional memory system.
That may be partly why there are a plethora of anecdotes about how sensory cues, out of context, can take you right back to emotional memories – perhaps you associate the scent of a certain perfume or cologne with your first kiss because the memory is higher fidelity.

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With a fearful experience, our survival systems kick into action, and we can achieve what’s known as a single trial memory. “If you escape from a lion once, or you see someone else being eaten by a lion, you know to be afraid of that lion,” explains Kerry Ressler, a professor of psychiatry and behavioural sciences at Emory University in Atlanta, Georgia. That's very different from something like studying facts in a book, and activities that aren’t emotionally arousing. “That may make sense evolutionarily, because we want to prioritise things that are really important,” explains Ressler.
When we feel fear, a burst of adrenaline activates a cascade that is thought to enhance memory storage of the immediately preceding events. “The fear system has evolved to keep us alive,” says Karim Nader, a psychology professor at McGill University in Montreal, Canada.
Flashbulb memories
Fearful experiences may not always lay down strong memories, however. Elizabeth Phelps, a professor of psychology and neural science at New York University, was interested in people’s so-called “flashbulb memories” of 9/11. These are not individuals with PTSD, “but everyday people who had experienced 9/11, which was most of us”, says Phelps. And curiously, she found that, vivid as these memories feel, they were not as strong as people believed – they could be changed.

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Phelps’ lab at NYU was near the thick of the disaster. In a large-scale detailed survey conducted first within a few weeks of 9/11, then one year, two years, and 10 years later, they found that “people were very confident that the details of their memory were correct”. Not the detail in terms of the fact that it happened, but where they were, who they were with, how they first heard about it, and what they did afterwards. However, personal recollections of the contextual details often actually changed with time.
This suggests, says Phelps, that flashbulb memories differ from memories of more neutral events not because the details of the memory are preserved any better, but because we think they are. “With highly traumatic events we think we have this incredibly accurate memory,” she says. The truth is, many of the details we think are accurate are not. “Emotion focuses your attention on a few details, at the expense of a lot of others,” explains Phelps.
Total recall
So, could this mean that traumatic memories can be manipulated, even removed? Based on an emerging understanding of the storage and retrieval of memory, we have windows of opportunity for altering the closure of fearful memories in the brain. The time window for dampening the initial locking-in of memories, explains Nader, is on the order of 6 hours. So pharmacological approaches to lessen the strength with which a distressing memory is locked into the brain need to be administered within that short window. Indeed, there is emerging evidence from rodent and human studies that drugs called beta-blockers can achieve a reduction in later PTSD symptoms if administered quickly. “The Israeli military now use that,” says Nader. But new research is suggesting that even beyond the short window during which memories are saved to the internal hard drive of our brain, they can be retrieved, updated, and toned down.

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Experimenting with rats, Nader reminded animals of a conditioned fearful memory with a musical tone (previously linked to an electric shock), and subsequently administered a beta-blocker. Even after the beta-blocker was eliminated from the blood, the fearful freezing response to the memory was gone. Exploring the same approach in a small sample of humans, Nader and colleagues determined that despite an average of 11 years between trauma and experimental intervention, “even after the beta-blocker was eliminated from the blood, their trauma was down to non-PTSD levels”. It’s still early days for this method, and studies of its efficacy are ongoing.
Still, by using what we know about reconsolidation as a potential therapeutic tool, it seems that a subtle form of memory reprogramming is within reach. “We’re not changing your knowledge of what happened. We’re just changing its association with these fight or flight stress responses that we get”, says Phelps. “So the notion that we’re going to be able to erase your knowledge of what happened – that’s science fiction at this point.”
Departure points
As for McKinnon, she admits that despite her vividly traumatic experience, there are many details she can’t remember.
“We were over the top of the island and then the plane veered back over the ocean, which was incredibly scary, because then we thought ‘that was it’,” says McKinnon, recalling the moment that AT 236 approached the Lajes landing strip. She remembers seeing the tops of houses, and worrying about crashing there and killing other people. But asked if the plane was in darkness during its terrifying descent, McKinnon says, “I have to be honest with you – I entirely don't remember.” Nor can she remember whether or not she was sitting beside the window.
When it comes to terrifying memories, perhaps our brains are selective in what details are stored. The more we learn about how and why, the closer we’ll get to lessening the impact of trauma.
That fated honeymoon flight was an eventful way to begin a marriage. “It was quite a start, yes,” McKinnon laughs. “Unexpected.” It proved to be a life-changing year in more than one way: making her aware of the need for research, but also for better care and treatment for PTSD, she says. “And that was the direction I wanted to take my career in.” McKinnon’s experience that day was the start of an unforeseen new personal and scientific journey. As time goes by, the memory may be harder to remember, but the legacy is hard to forget.

BBC.