Sensing Infrared Light Has Much
In 2004, Eric Thomson, fresh from finishing his Ph.D. in neuroscience at the University of California, San Diego, was
seeking his next challenge.
He visited a variety of laboratories across
the country, but wasn’t quite enthused with
the potential research avenues available for
His interests lay in touch processing,
specifically with freely moving laboratory
rats. However, many of the labs he visited
were resistant to that kind of work, opting to
run experiments on anaesthetized and fixed
animals rather than freely moving creatures.
Then, he found Dr. Miguel Nicolelis,
principal investigator of Duke University
School of Medicine’s Nicolelis Lab.
“He was back then doing pretty cutting-edge work, and implanting multi-electrode
arrays in freely moving rodents, doing
interesting behavioral tasks,” said Thomson.
In Nicolelis, Thomson found someone who
wasn’t afraid to ask tough questions and tackle
complex issues. He signed up for the ride.
Twelve years later, Thomson is still there.
He’s now a research scientist with the
Nicolelis Lab, which is still on the cutting
edge and pushing boundaries.
A “scientific playground,” as described by
Thomson, the Nicolelis Lab is a fast-paced
environment led by someone who is often a
few steps ahead of his researchers.
“We try to keep up,” Thomson said. “I’ve
never really worked with anyone quite like
him. That’s the reason I decided to stay with
Located on Duke University’s campus,
the Nicolelis Lab is home to an array of
experiments. One of Thomson’s colleagues
is working on a spinal stimulation
technique for Parkinson’s disease, another is
experimenting with brain-to-brain interfaces
for rats, and others are enabling primates to
control exoskeletons and wheelchairs with
their neural activity.
Meanwhile Thomson, who relishes the
nitty-gritty of an experiment, is endowing
rats with the ability to sense infrared light.
A handful of years ago, Nicolelis
approached Thomson with an idea. He
wanted to see if it was possible to bypass
a rat’s normal sensory transducers, which
transfer information from the five senses to
the brain. Using off-the-shelf components,
Thomson designed the experiment. He
attached a single infrared detector to
the heads of adult rats. After sensing
infrared light, the detectors would send
the information to the rats’ somatosensory
cortex, a receptive area for touch.
Rats have a particularly advanced
somatosensory cortex, Thomson said.
“Just like we have a disproportionally large
part of our cerebral cortex devoted to visual
processing, they have a disproportionally
large part of their cortex devoted to whisker
processing,” he said. “So, it’s a real nice model
system for somatosensory processing in
In the experiment, the rats were given a
myriad of reward ports to choose from, one
of which would display infrared light.
Days went by, and then weeks. The rats
didn’t seem to understand there was an
association between the correct port and the
microstimulation they felt in their brains.
Error tones buzzed, distressing both the rats
“We almost gave up on this project,”
Thomson said. “We had to tweak so many
Then, a breakthrough. After about 30
days, the rats started sweeping the sensors
mounted to their heads, as if searching
the environment with “a cyclopean eye,”
“They were finally trying to forage and
sample the (infrared) environment, rather
than randomly going to those ports like they
didn’t know what was going on,” he added.
“Kind of like a heat seeking missiles, they
honed in on their target.”
Nature Communications published a paper
on the experiment in 2013. For Thomson,
In the succeeding years, Thomson and
colleagues decided to increase the experiment’s
capacity. This time around, they implanted four
infrared detectors in the rats’ brains. Thomson
was unsure whether the higher amount of
microstimulation would help them learn more
quickly, or just overwhelm and confuse them.
“This wasn’t just an idle worry,” he said. “This
was actually a very real fear for me.”
But the rats rose to the occasion. Instead
of 30 days, they learned how to perform the
task in around 4. 5 days.
“I was frankly astounded because I’ve
never had my rats learn any task in four and
half days, much less learn to discriminate a
completely new sensory modality that they’ve
never experienced before,” Thomson said.
It suggests that the brain “is very happy to
exploit and take advantage of that increase in
While it appeared like the rats were using
the infrared detector like a new visual
modality, Thomson was unsure whether that
was actually the case. “Are they experiencing
it like vision?” he wondered. Or “are they
experiencing it like touch and they’re just
associating a tactile sensation with this stuff
in the environment? I have no idea.”
The issue raises philosophical questions
regarding subjective experience. And since
one can’t ask a rat what they’re experiencing,
one can only speculate. It’s an even bigger
unknown for humans.
According to Grazyna Palczewska, the
director of medical device development for
biotech company Polgenix Inc., the human
visible spectrum is limited to wavelengths
between 400 and 720 nanometers. But
previous studies have indicated humans may
be able to sense infrared wavelengths. In 1947,
researchers reported that at wavelengths above
800 nm, rod photoreceptors became more
sensitive than cones and allowed people to see
infrared as white light.