ADVANCES
14 Scientific American, June 2019
Illustration by Thomas FuchsJapanese strain but faster than the Aus-
tralian one and also opted for the
highest-quality grub.
The speedy Japanese slime
mold would likely have an edge
in places where resources are
scarce and competition is high,
making any food better than no
food, the researchers reported in
February in the Proceedings of
the Royal Society B. The Austra-
lian strain might be better suited
to resource-rich environments in
which slow decision-making would
maximize nutritional benefits. The
American strain would probably thrive in
both environments.
These findings add an ecological spin to
the growing body of work on decision-mak-
ing capabilities in the simplest organisms,
says James Marshall, a theoretical and com-
putational biologist at the University of
Sheffield in England, who was not involved
in the study. “Taking longer over making
the right decision can make sense in isola-
tion, but when competing with others,
being quick but inaccurate can be better.”
— Rachel NuwerBEHAVIORAL BIOLOGY
Slimy Smarts
Slime molds engage
in complex, varied
decision-making
In the film The Wizard of Oz, the
scarecrow famously pines for a brain
but eventually comes to realize that
he already possesses all the smarts he
needs. Similarly, acellular slime molds—
strange, gelatinous organisms that con-
sist of a single cell with billions of nuclei—
lack a brain yet sometimes act like far
more sophisticated creatures.
“We can’t say that slime molds have per-
sonalities, because people would be very
upset,” says Audrey Dussutour, a behavioral
biologist at Toulouse University III–Paul
Sabatier in France. But “these giant cells
have quite complex behaviors and display
different ways of making a decision.”
Dussutour and her colleagues were
interested in studying how three strains of
a particular slime mold species handle
trade-offs between speed and accuracy
BIOTECH
Sonic Therapy
Ultrasound stimulation through
skin could treat inflammation
Ultrasound is used widely in medical
imaging, but in recent years scientists have
started honing it for another use: stimulat-
ing nerves to treat disease. In two new
studies in rodents, researchers focused
the sonic vibrations on nerves in the spleen
that communicate with the immune
system, reducing inflammation. If the
approach proves safe and effective in
people, it could serve as a noninvasive
treatment for inflammatory diseases such
as rheumatoid arthritis.
About 20 years ago neuroscientist Kev-
in Tracey and his colleagues discovered
that brain signals traveling along the vagus
nerve exert control over the immune sys-
tem. “These [signals] are primitive reflexes
that arise in the brain stem, evolved to pre-
serve the integrity and health of cells in the
body,” says Tracey, president and CEO of
the Feinstein Institute for Medical Research
in Manhasset, N.Y. Stimulating the nerve is
a way to hack into those reflexes.
The vagus nerve consists of a bundle
of fibers that branch into many organs. It
connects with the immune system via a
second nerve that innervates the spleen,
where circulating immune cells make
a stop before flooding the bloodstream
again. The new studies, published in
March in Nature Communications, suggest
that sending ultrasound to the spleens
of mice through their skin may hit the
nerve endings and could be just as effec-
tive as directly stimulating the vagus
nerve. The latter requires surgically
implanted electrodes.
In one study, led by Tracey’s colleagues
at the Feinstein Institute and GE Research,
rats receiving a few minutes of ultrasound
treatment to the spleen nerve had a dimin-
ished inflammatory response to an injected
toxin. In another study, researchers at the
University of Minnesota and their colleaguesreduced symptoms of inflammatory arthritis
in mice by stimulating their spleen nerves for
20 minutes every day for a week. Zeroing in
on the spleen may provide a more precise
approach than focusing on the vagus nerve,
says Hubert Lim, lead author of the latter
study. “When we’re targeting the spleen,
we have less of an effect all over the body.”
Little is known about how repeated
ultrasound affects the spleen or whether it
has other harmful effects, says neuroscien-
tist Denise Bellinger of Loma Linda Univer-
sity, who was not involved in either study.
An ongoing clinical trial aims to assess the
treatment’s safety in humans with rheu-
matoid arthritis. A bigger unknown is how
ultrasound activates nerves in general. Sci-
entists are now exploring the use of ultra-
sound on other parts of the nervous sys-
tem, including the brain. “We know how
to control nerves with electricity, and
we’ve been doing it for more than 100
years,” Tracey says. “But the idea of control-
ling nerve signals with ultrasound is a
brand-new field.” — Bahar Gholipourwhen trying to find food. After presenting
strains native to Japan, Australia and the
U.S. with food sources of varying quality,
the researchers observed which ones the
organisms chose to engulf and consume.
The Japanese strain acted quickest, ran-
domly selecting whatever food it found.
The Australian strain took longest but typi-
cally chose the best food. The American
slime mold decided more slowly than the