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machado: why does smell trigger memories more than any other sense?

seeing, hearing, touching, and tasting something is the stuff that many memories are made of, but the process of remembering is slower, and the effect less intense than a recollection triggered by smell.

by lisa machado

oct 24 2022

7 minute read

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what's the secret to managing triggers that bring back the past?

the connection between smell and memory is not quite fully understood. getty

when i was a teenager, all my friends loved the store lush.

offering a stinky (in a good way) earth-friendly collection of colourful soaps, cosmetics and body products, the lush scent was — and still is — an overwhelming, pungent wave of herby fruitiness that can, literally, be smelled a mile away. racked called the smell “a squeaky-clean flower assassin that slips up your nose and commands your attention.”

the location we liked most was on queen street west in toronto. not only located in a cool part of town, it was also near to the bamboo club, a venue frequented by artists who would go on to become some of world’s top reggae musicians. and the pad thai was phenomenal.

i was never a lush fan — my skin screamed if i even as much as thought about a sparkly purple bath bomb or the “skin’s shangri la” with bladderwrack seaweed extract moisturizer. but years later, every time i catch a the scent of a lush store, my mind is flooded with vivid details of the bamboo’s uneven dance floor, the way the thick cigarette smoke hung in the air, and the slow, sweet, sensual reggae beat that made it impossible not to sway in the darkness.

and while just a whiff of a lush “blue skies and fluffy white clouds” bubble bar is enough to get me humming something from the sattalites, for a friend of mine, the same aromatic bubble bar brings on anxiety, fear and very deep sadness.

a few years ago, she lost her sister after she was killed in a violent attack while walking home from work. a creative, easy-going person, she loved bright colours, particularly rainbows, and all things lush. my friend describes visiting her sister’s apartment and stopping into her small bathroom to check out the colourful soaps that lined the shelves as her sister yelled each of their over-the-top names from the living room.

“for holidays and occasions, everyone in the family knew that at some point, a box of lush would appear as a gift,” she says. “even for the kids. she just loved it so much.”

it wasn’t until months after her death that my friend would realize just how closely she associated the powerful fruity scents with her beloved sister. she passed a lush store on the way to a work meeting and found herself sobbing uncontrollably outside on the sidewalk. she says that it was like the heavy fragrance had triggered all of the painful details about her sister’s death and sent them rushing through her veins right at that moment: conversations with the police, hushed court proceedings and the pain of emptying her sibling’s apartment.

one of the last times i saw my brother alive was at princess margaret cancer centre. i left him to finish his blood tests, walked through the pharmacy where two huge electronic blue screens were loudly beeping — one to signal it was a first call, three beeps was a final attempt — to let patients know their prescriptions were ready. next, i shuffled between two covid screening stands where the air was heavy with the medicated stench of hand sanitizer and then out the front door into the bustle of university avenue during rush hour.

there is an exact spot on the hospital steps that — even more than a year since his death — reminds me of all the times i watched him limp slowly across the street to his parked car, and then turn to smile and wave. but there’s something about the smell of hand sanitizer, and the stink of car exhaust that brings these memories careening to the forefront of my mind in huge, blinding images: the colour of his shoes, the way he laughed with a little crackle in his throat when i told him he was handsome, the dots of yellow in his hazel-coloured eyes.

there’s no question that our sense of sight, hearing, touch and taste play an important role in memories, but, according to the experts, none of them have the ability to take you down or lift you up the way smell does. and there’s a completely logical scientific reason why.

while seeing, hearing, touching, and tasting something is the stuff that many memories are made of, the process of remembering through these senses is slower, and the effect tends to be less intense than when recollections are triggered by smell. when we see, hear, feel or taste something, that information first heads to the thalamus — often referred to as the brain’s relay station — which then sends the information to other parts of the brain for processing, such as the hippocampus (responsible for memory) and the amygdala (responsible for emotions).

but smells have a stronger tie to memory and emotion, bypassing the thalamus and going straight to the olfactory bulb, known as the brain’s “smell centre,” which is directly connected to the amygdala and hippocampus, according to discovery. smells don’t dawdle. it’s this direct link that experts say may be the reason why odours quickly trigger detailed memories, really intense emotion, and as psychology today puts it, the feeling of “being brought back in time.”

and sure, it’s nice when “scent memory” brings back warm and fuzzy feelings from the past — for example, the smell of gasoline reminds me of carefree saturday mornings when my dad would lie underneath his 1969 buick (named betsy), fixing something as my brother and i laid on our bellies drawing pictures with chalk on the driveway.

it’s not so great, though, when smells bring up disturbing memories and emotions that cause us pain and distress.

“smell is very deeply ingrained in our emotional memory,” eric vermetten, a clinical psychiatrist and trauma researcher at leiden university medical center in the netherlands, told nature.

after counselling a vietnam war veteran who couldn’t sleep because the smells of the asian food restaurant that he lived above reminded him of his experiences in the war, vermetten embarked on research to delve into how odours trigger traumatic memories. (data from the military suicide research consortium (msrc) shows that many veterans are negatively affected by smells like gunpowder and flammable liquids. another study found that 93 percent of combat veterans with post-traumatic stress disorder (ptsd) reported being distressed by the smell of burning rubber.)

using 16 vietnam war combat veterans, half with (ptsd) and half without, vermetten and his team exposed them to three smells: diesel, which was closely associated with traumatic war experiences; the cozy smell of vanilla; and the unpleasant stench of hydrogen sulfide, which had no connection with war.

when they measured the brain activity of the veterans, they recorded that the diesel smell caused increased blood flow to the amygdala — the part of the brain associated with fear — in the veterans with ptsd, and had less of an effect on the others. the former group also rated the diesel smell as more distressing than the latter group.

and although the connection between smell and memory is not quite fully understood, recognizing the impact that scents can have on mental health has prompted researchers to study the potential of using smells to relieve people of traumatic memories. vermetten suggests that perhaps people being treated for trauma can be “calmed” or “reset” using scents that are not connected to their triggers — for example, coffee grounds could be given to someone remembering a traumatic war memory in order to bring them back to the present.

similarly, florida state university psychology researchers wen li and brad schmidt set out to see if the link between smells and traumatic memories could be broken by “retraining” veterans to be able to discern between when the triggering scent was a danger and when it wasn’t.

“ptsd patients can’t differentiate between a minimum-level smell and a threat-level smell,” li said in an interview with msrc. “they see a little bit of ‘red’ in everything. they pay attention to the small amount of red signal, while in healthy controls this will be dismissed. we want to train them to dismiss this small amount of threat signal while maintaining their ability to detect something that is truly a threat.”

li’s exercise involved “morphing” odours, for example, taking something that might be an anxiety-causing scent, like gasoline, and mixing with something else to weaken the smell to create “a psychological distance between a minimal, insignificant [threat] signal and a real signal.”

unfortunately, li’s work lost funding and she wasn’t able to continue the study, but she told msrc that she hoped “retraining” would someday be another way psychologists can help reduce the risk of suicide among veterans.

of course, there are other ways to manage traumatic memories such as meditation, identifying and avoiding triggers, and therapy. talking to others, writing down your thoughts and a healthy lifestyle can also help, brandon van niekerk writes for overcomers counseling. he suggests that how long you struggle with triggers that bring on disturbing thoughts and feelings can depend on things like how much support you have, how long ago the event happened and whether or not you have received professional help.

still, even with strategies to manage them, traumatic memories don’t just disappear — for many people they barely fade. and regardless of how they are triggered, whether by something that’s heard, tasted or smelled, if we’re lucky, we find a way to cope and move through them. and if we are luckier, there are more good memories to be reminded of in our lives than bad.

here’s to a little more bamboo.

lisa machado is the executive producer of healthing.ca.

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lisa machado

lisa machado began her journalism career as a financial reporter with investor's digest and then rogers media. after a few years editing and writing for a financial magazine, she tried her hand at custom publishing and then left to launch a canadian women's magazine with a colleague. after being diagnosed with a rare blood cancer, lisa founded the canadian cml network and shifted her focus to healthcare advocacy and education.

machado: why does smell trigger memories more than any other sense?

seeing, hearing, touching, and tasting something is the stuff that many memories are made of, but the process of remembering is slower, and the effect less intense than a recollection triggered by smell.

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machado: why does smell trigger memories more than any other sense?

seeing, hearing, touching, and tasting something is the stuff that many memories are made of, but the process of remembering is slower, and the effect less intense than a recollection triggered by smell.

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