The Scientist - USA (2020-05)

24 THE SCIENTIST | the-scientist.com

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A

mouse finds itself in a box it’s never seen before. The

walls are striped on one side, dotted on the other. The

orange-like odor of acetophenone wafts from one end

of the box, the spiced smell of carvone from the other. The

mouse remembers that the orange smell is associated with

something good. Although it may not recall the exact nature

of the reward, the mouse heads toward the scent.

Except this mouse has never smelled acetophenone in its life.

Rather, the animal is responding to a false memory, implanted in its

brain by neuroscientists at the Hospital for Sick Children in Toronto.^1

Sheena Josselyn, a coauthor on a 2019 Nature Neuroscience

study reporting the results of the project, says the goal was not to

confuse the rodent, but for the scientists to confirm their under-

standing of mouse memory. “If we really understand memory, we

should be able to trick the brain into remembering something that

never happened at all,” she explains. By simultaneously activating the

neurons that sense acetophenone and those associated with reward,

the researchers created the “memory” that the orange-y scent her-

alded good things.

Thanks to optogenetics, which uses a pulse of light to activate

or deactivate neurons, Josselyn and other scientists are manipulat-

ing animal memories in all kinds of ways. Even before the Toronto

team implanted false memories into mice, researchers were making

rodents forget or recall an event with the flick of a molecular light

switch. With every flash of light, they test their hypotheses about how

these animals—and by extension, people—collect, store, and access

Strategies to make lab animals forget, remember, or experience false recollections

probe how memory works and may inspire treatments for neurological diseases.

BY AMBER DANCE

Manipulating

Memory