The next treatment for trauma could be spotless minds.
Down Memory Lane
The human brain has roughly 100 billion neurons and can store about
2.5 petabytes of information. But where you put your keys last night?
The answer is always suspiciously unavailable.
Sam Kaplan
Researchers have
known for decades that memories are unreliable. They’re particularly
adjustable when actively recalled because at that point they’re pulled
out of a stable molecular state. Last spring, scientists published a
study performed at the University of Washington in which adult
volunteers completed a survey about their eating and drinking habits
before age 16. A week later, they were given personalized analyses of
their answers that stated—falsely—that they had gotten sick from rum or
vodka as a teen. One in five not only didn’t notice the lie, but also
recalled false memories about it and rated that beverage as less
desirable than they had before. Studies like these point to possible
treatments for mental health problems. Both PTSD and addiction disorders
hinge on memories that can trigger problematic behaviors, such as
crippling fear caused by loud noises or cravings brought about by the
sight of drug paraphernalia.
Studies have found chemical compounds that can be used to subdue or even delete memories.Several
studies have found chemical compounds that can be used to subdue or
even delete memories in mice (and maybe someday in people). In June, a
report led by an Emory University researcher showed that SR-8993, a drug
that acts on the brain’s opioid receptors, can prevent a fear memory
from forming. Researchers strapped mice to a wooden board for two
hours—a stressful experience that later gave them a heightened sense of
fear similar to PTSD. But mice given SR-8993 before or after the
stressful incident were less likely to end up this way. Another study
identified a drug, Latrunculin A, that can erase memories days later.
The researchers trained rodents to consume methamphetamine in an
environment with distinctive visual, tactile, and scent cues such as
black walls, gridded floors, and the scent of vanilla or peppermint.
Rodents that were injected with Latrunculin A two days later didn’t seek
out meth when returned to that environment, but others did. Latrunculin
A is known to mess up scaffolding that supports connections between
neurons. Considering how broadly these two drugs affect the brain,
there’s a possibility of serious side effects.
To
make more targeted treatments, researchers will ultimately need to
understand how the brain’s neurons encode each memory. Last year, Susumu
Tonegawa at the Massachusetts Institute of Technology reported that
individual memories in mice leave telltale molecular signatures in the
brain’s hippocampus region. In July, his group caused mice to falsely
associate an old memory with a new context—essentially creating a false
memory. First, they genetically engineered a mouse so that when its
hippocampal cells were activated, they would be tagged with a protein
that the researchers could switch on later. Then, they put the mouse in
an unfamiliar cage. The next day, they moved it to a strikingly
different cage (smelly with black walls). Then, at precisely the same
time, they gave it an uncomfortable shock and switched on the tagging
protein to briefly activate cells that had been active in the old cage.
When they put the mouse back in the old cage, it froze as if afraid—as
if it had a false memory of being shocked there.
The
idea of scientists manipulating memory does, naturally, sound a bit
creepy. But it also points to some possible good: treatment for millions
of people tormented by real memories. And that’s something worth
remembering.
This article originally appeared in the December 2013 issue of Popular Science.
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