20 THE SCIENTIST | the-scientist.com
COURTESY OF HUMMbers of the tACS group being able to recall six
items, while the control group remembered
only five. In addition, she adds that it remains
to be seen if similar improvements can be
seen with other working memory tasks.
Other scientists share Liu’s skepticism.
Because the company didn’t report whether
or not their memory patch generated any
changes in the brain, it is unclear whether it
actually alters brain rhythms, says Joel Voss,
a neuroscientist at Northwestern University
who has no affiliation with the company. “It’s
important if you want to validate a device to
show that it’s actually engaging the hypothe-
sized neural structure and changing its func-
tion in the way that you predicted.” Other-
wise, Voss adds, the effects could be due to
“extraneous, nonspecific influences,” such as
placebo or indirect influences on the periph-
eral nervous system. For example, stimulat-
ing the nerves on your skin might make you
alert, which may in turn make you more
attentive to the task at hand.
On top of that, it remains unclear how
much electricity actually enters the brain
with tES, according to Voss. He adds that
results from several studies indicate that
not enough electricity gets into the brain
with this technique to have a meaning-
ful impact on function. For example,in one 2019 Nature Communications
paper, a group of researchers reported
that tACS stimulation could increase
a tremor in individuals whose hands
already shook and trigger it in healthy
individuals asked to hold a tiny weight
up with one finger. But this effect dis-
appeared when they applied a topical
anesthetic to the skin on participants’
heads before placing the electrodes,
hinting that the original effect may have
depended on stimulating peripheral
nerves, rather than on electricity reach-
ing the brain. Liu and her team have
generated similar findings by measuring
neural activity directly from the brains
of epilepsy patients undergoing surgery,
observing that tACS failed to influence
memory-related brain waves.
Still, Zanto and McIntyre are opti-
mistic about the future of this technology.
McIntyre points out that in another 2019study, which was published on the pre-
print server bioRxiv, a different group of
researchers demonstrated that, even after
using a local anesthetic to block skin sensa-
tions during tACS in non-human primates,
electrical stimulation was able to entrain
the firing of neurons in the animals’ hippo-
campuses, a memory-associated region deep
within the brain. While the mechanism of
action of tACS remains an open question,
“I don’t think you can completely explain
away the huge literature showing the effects
of neural stimulation,” says Zanto. “If it
were a placebo effect, why do people show
time and time again changes in cognitive
function when paired to a group that gets
a placebo control?”
The Humm team plans to conduct fur-
ther studies of the memory patch in order
to answer questions such as whether a tACS
session will improve performance on other
tasks. “We have a laundry list of scientific
questions that are of interest,” says Zanto.
For now, the company is accepting online
registrations for early access to its patch—
currently a single-use device that costsPOWER STRIP:This electrode-containing patch
could boost working memory, according to Humm,
the California-based company that makes it.I don’t think you can completely
explain away the huge litera-
ture showing the effects of
neural stimula tion.
—Te d Zanto, University of California
San Francisco