It was the day before Christmas, and the normally busy MIT laboratory on
Vassar Street in Cambridge was quiet. But creatures were definitely stirring
, including a mouse that would soon be world famous.
Steve Ramirez, a 24-year-old doctoral student at the time, placed the mouse
in a small metal box with a black plastic floor. Instead of curiously
sniffing around, though, the animal instantly froze in terror, recalling the
experience of receiving a foot shock in that same box. It was a textbook
fear response, and if anything, the mouse’s posture was more rigid than
Ramirez had expected. Its memory of the trauma must have been quite vivid.
Which was amazing, because the memory was bogus: The mouse had never
received an electric shock in that box. Rather, it was reacting to a false
memory that Ramirez and his MIT colleague Xu Liu had planted in its brain.
“Merry Freaking Christmas,” read the subject line of the email Ramirez
shot off to Liu, who was spending the 2012 holiday in Yosemite National Park.
The observation culminated more than two years of a long-shot research
effort and supported an extraordinary hypothesis: Not only was it possible
to identify brain cells involved in the encoding of a single memory, but
those specific cells could be manipulated to create a whole new “memory”
of an event that never happened.
“It’s a fantastic feat,” says Howard Eichenbaum, a leading memory
researcher and director of the Center for Neuroscience at Boston University,
where Ramirez did his undergraduate work. “It’s a real breakthrough that
shows the power of these techniques to address fundamental questions about
how the brain works.”
The prospect of tinkering precisely with memory has tantalized scientists
for years. “A lot of people had been thinking along these lines,” says
Sheena Josselyn, a senior neuroscientist at the Hospital for Sick Children
in Toronto, who studies the cellular underpinnings of memory, “but they
never dreamed that these experiments would actually work. No one ever
thought that you could actually, really do this.”
Except Ramirez and Liu. Their work has launched a new era in memory research
and could someday lead to new treatments for medical and psychiatric
afflictions such as depression, post-traumatic stress disorder and Alzheimer
’s disease. “The sky is really the limit now,” says Josselyn.
Though the work so far has been done on lab mice, the duo’s discoveries
open a deeper line of thought into human nature. If memories can be
manipulated at will, what does it mean to have a past? If we can erase a bad
memory, or create a good one, how do we develop a true sense of self? “
Memory is identity,” the British author Julian Barnes writes in his memoir
Nothing to Be Frightened Of. “You are what you have done; what you have
done is in your memory; what you remember defines who you are.”
