Reader\'s Digest Canada - 04.2020

But those studies were all based

on  observed behaviours. A team of

researchers led by Lilianne Mujica-

Parodi, of Stony Brook University in

New York State, wanted to look deeper.

They decided to use an fMRI scanner

(which tracks blood flow to measure

brain activity in real time) to deter-

mine whether exposure to human

fear-sweat provoked a measurable

reaction in another human’s amyg-

dala, the key brain structure that trig-

gers our fear response.

They started by collecting sweat from

144 people who were participating in

a first-time tandem skydive. Then they

used those same 144 individuals as their

own controls, collecting their sweat

after they’d run on a treadmill for the

same length of time that the skydive

had lasted and at the same time of day.

“Because the tandem master con-

trolled the descent,” the researchers

wrote later, “the skydiving condition

produced a predominantly emotional

but not physical stressor for our sweat

donors, while the exercise condition

produced a predominantly physical but

not emotional stressor.” (They confirmed

the first-timers’ emotional stress by

testing their levels of cortisol, a hormone

released by our adrenal glands in con-

nection with our fight-or-flight response.

Sure enough, they had spiked.)

Then came phase two: presenting

the sweat samples to test subjects and

using fMRI scans to view how their

brains reacted in real time. They

showed that when a subject inhaled

sweat taken from a stressed or fearful

person, their amygdala was activated.

In a secondary procedure, they had

also shown that what was happening

wasn’t about smell, exactly. Our noses

can’t distinguish between fear-sweat

and regular, everyday exercise-sweat,

but our brains react differently to the

two. That’s what’s known as a chemo-

sensory reaction: the pheromones in

the fear-sweat trigger our emotional,

not our olfactory, sensors.

Then they took it one step further.

The researchers hooked another group

of test subjects up to an electroenceph-

alogram (EEG) machine. Basically, an

EEG lets researchers see which parts

of the brain are reacting to a given

stimulus. Once they were wired and

ready, the subjects were exposed to

both fear-sweat and exercise-sweat

WE CAN SMELL FEAR ON EACH OTHER.

IT PREPARES YOUR BRAIN TO REACT TO

INCOMING THREATS.

reader’s digest

90 april 2020