The Scientist November 2018

11.2018 | THE SCIENTIST 19

neuroscientist Mark D’Esposito and his colleagues are using TMS
with a different, much shorter protocol—lasting only about 40
seconds. They recently discovered that targeting hippocampal
networks using this approach could improve the encoding of new
memories (J Cogn Neurosci, 30:1452–72, 2018). “It’s always good
when that happens—slightly different methods but coming to the
same conclusions,” says Arielle Tambini, a postdoc in D’Esposito’s
lab and lead author on the study.
More common than magnetic stimulation, though, is the use
of electrical pulses in a technique known as transcranial alternat-
ing current stimulation (tACS), which a growing body of litera-
ture suggests can also boost aspects of memory. “The number of
studies that show a positive effect is becoming substantial,” says
Nick Ketz, a memory researcher at HRL Laboratories in Malibu,
California, who recently coauthored a study on the use of tACS to
improve memory consolidation during sleep (J Neurosci, 38:7314–
26, 2018). “It’s enough that people are taking notice of it.”
But some researchers question the effectiveness of tACS. “It’s
still not widely accepted, because the mechanism for influence
is still a little bit unknown or unreliable,” says Ketz. “We haven’t
determined why it works in some cases and not in others.” More-
over, he adds, noninvasive techniques are “still pretty coarse.”
During tACS, the scalp and the skull diffuse the voltage, so “it’s
hard to know where the current is going to flow,” Ketz says. Magnetic
stimulation isn’t influenced by the scalp, and as a result, researchers
using methods such as TMS can aim at a specific swatch of cortex
more precisely. “We can be much more specific in terms of targeting
this brain region versus another brain region that’s just a couple of
centimeters a w a y,” says Tambini.
But all noninvasive approaches face additional shortcomings,
says Jon Willie, a neuroscientist and neurosurgeon at Emory Uni-
versity School of Medicine. “Effects may be weak,” he notes in an
email to The Scientist, and “it can be hard to distinguish the effects
of arousal, attention, etc., from a specific effect on memory.”
When it comes to noninvasively stimulating the brain to boost
memory, “really there are more questions than answers yet,” agrees
Voss, so it’s too soon to make claims about the use of these tech-
niques for treating Alzheimer’s disease or other brain disorders.
For example, he says, “we don’t know what the stimulation is
doing.... What’s actually going on neurally is quite a mystery still.”
—Jef Akst

Rewired

About three years ago, a six-year-old boy in Pittsburgh under-
went surgery to remove a large part of the right side of his brain.
Identified publicly as “U.D.” by doctors, the boy suffered from epi-
lepsy, and drugs were not helping to control his seizures. His doc-
tors and his parents decided that taking out U.D .’s right occipital
and posterior temporal lobes would be the best way to improve
his quality of life. But the medical team was not certain how the
surgery would affect the boy’s ability to recognize visual images

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