ADVANCES
10 Scientific American, April 2019
ETHAN DANIELSGetty Imagesimplan table device that could help people
with brain injuries decode and interpret
everyday scents.
Research on smell lags decades behind
that on vision and hearing, says Joel Main-
land, an olfactory neuroscientist and associ-
ate member of the Monell Chemical Senses
Center in Philadelphia, who is not involved
in the new work. Smell studies receive less
funding than research on other senses does,
he says. And smell involves many sensory
components. Whereas vision requires inter-
preting input from three types of receptors,
taste involves 40 and olfaction 400.
A surprisingly large number of people
have an impaired sense of smell—23 percent
of U.S. adults age 40 and older, according
to one national survey, and 62.5 percent of
those age 80 and older, according to anoth-
er. Such a decline can result from injury,
chronic sinus problems, genetics or aging,
says VCU professor Richard Costanzo, who
has studied smell for four decades and is
co-leading the initiative to develop the new
device. Often dismissed as inconsequential,
smell contributes to taste, so people who
cannot smell are at risk for malnutrition,
as well as social isolation, Costanzo says.
Some smell-restoration treatments
exist, Mainland says, including smell train-
ing, in which people repeatedly expose
themselves to certain odors and practice
identifying them. Other treatments may
uncover specific causes of smell loss, such
as chronic sinusitis. But for someone with
the damage Moorehead suffered, none of
these is effective.
Smell, like all senses, is a multistep pro-
cess. Scents, technically called odorant
molecules, enter through the nose or
mouth and pass through a layer of mucus
before binding to olfactory receptor neu-
rons. This binding triggers electrical signals
that reach certain spots in the brain’s olfac-
tory bulb. “One nerve cell may respond to
a brownie but not to pound cake, and its
neighbor might do the opposite,” says Eric
Holbrook, chief of rhinology at Massachu-
setts Eye and Ear Hospital and an associate
professor at Harvard Medical School. “One
nerve cell probably responds to multiple
chemicals, but they have some specificity.”
Holbrook, who is collaborating with the
VCU team, is now trying to find a shortcut
to stimulate the brain’s olfactory bulb and
then trigger a sensation of smell. Ultimate-
ly the researchers plan to create a device
that will operate somewhat like a cochlear
im plant, an electronic device that partially
re stores hearing. Cochlear implants turn
sounds into electrical signals that the brain
interprets; in a similar way, the VCU-Har-
vard team hopes to convert chemical scents
into useful electrical signals. Holbrook pub-
lished a study in February in the International
Forum of Allergy & Rhinology suggesting that
electrical stimulation in the nasal cavity and
sinuses can make a healthy person perceive
an odor, even if it is not present. That is a
long way from restoring a sense of smell in
someone who has lost it, but it is an impor-
tant step along the way, Holbrook says.
A cochlear implant has an external
sound processor worn behind the ear that
includes a microphone and microcomputer.
That component transmits signals to an
internal piece under the skin that stimulates
nerves in the cochlea, the organ that con-
verts sound vibrations into nerve impulses.
Similarly, the VCU-Harvard team envisions
a device that would potentially fit under the
nose—or on a pair of glasses—and include
an odor sensor and a small external micro-
processor, as well as an internal part to
stimulate different areas of the olfactory
bulb, Costanzo says.
Daniel Coelho, a cochlear implant sur-
geon at VCU who is collaborating with
Costanzo, says the researchers must still
refine sensors so they can discriminate
among enough odors to be useful. The
plan is to miniaturize and expedite smell
processing such as that carried out by so-
called electronic noses, which are used for
bomb detection and identification of
spoiled food. In addition, researchers must
determine the optimal surgical approaches
to safely implant a device that can stimu-
late the brain to perceive smells.
Developing such an olfactory implant
will take years, Coelho says, but it is not
impossible. “It’s a pretty straightforward
idea. We’re not inventing anything radically
new,” he notes. Rather the team is putting
existing technology together in a new way.
Moorehead, who injured himself falling
off a skateboard while trying to teach his
then six-year-old how to ride, is not opti-
mistic about regaining his sense of smell.
But he could not pass up the opportunity
to help others, including the researchers.
“It just kept seeming painfully obvious,”
Moorehead says, “that this is what I’m
supposed to do.” — Karen WeintraubM A R I N E B I O L O G YCoral
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But paleontologists have now dis-
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