Is fNIRS the Key to Locked-In Syndrome?


Everybody has something or other they fear the
worst.  For Indiana Jones, it was
snakes.  Surely high on many
people’s lists of horrors is the fate of falling victim to “locked-in
syndrome,” which is often the outcome of amyotrophic lateral sclerosis, a
disease that results from the death of motor neurons.  Two famous sufferers from the disease were baseball player
Lou Gehrig (which is why it’s sometimes called “Lou Gehrig’s
disease”) and physicist Stephen Hawking, who has survived for more than
five decades after his diagnosis. 
Most victims die within about three or four years of diagnosis, however.

A person with locked-in syndrome can usually
hear and see normally, but has lost the ability to move any voluntary
muscle.  Two-way communication with
such people has therefore been impossible up to now, although if even a single
eyelid can be moved voluntarily, such a low-data-rate channel can with patience
be used to good purpose.  As a
recent article in the MIT Technology
Review
notes, in 1995 Jean-Dominique Bauby suffered a stroke leaving him
locked in except for one eyelid, and he used it to dictate his memoirs.  But once the last voluntary muscle
nerves die, the door is shut, at least until recently.

The article reports on the work of a Swiss
neurological researcher named Niels Birbaumer, who has developed a system to
detect voluntary brain activity of locked-in-syndrome sufferers.  The most common means of monitoring the
brain is the electroencepalograph (EEG), but EEG signals are notoriously
difficult to interpret in terms of actual thought processes.  The most high-resolution way of
measuring activity in specific parts of the brain is currently functional
magnetic-resonance imaging (fMRI), which can focus in on millimeter-size
locations anywhere in the brain and monitor subtle changes in blood flow which
apparently correlate well with increased neuronal activity.  But fMRI rigs cost many hundreds of
thousands of dollars, are expensive to maintain and operate, and so are limited
to a few well-funded research sites.

A relatively new technique Birbaumer has helped
develop is called functional near-infrared spectroscopy (fNIRS), and can
non-invasively view blood-flow changes in the outer layers of the brain at much
less cost and in a more convenient way than fMRI.  Instead of the need to insert the patient’s head in a
liquid-helium-filled machine the size of a small car, fNIRS uses a cap-like
device that fits over the patient’s head. 
The cap holds emitters and sensors of near-infrared light in the
wavelength range of 700 to 800 nanometers (visible light is in the range of
about 400 to 700 nm).  This can be
done with inexpensive solid-state components, and the outputs are digitized and
analyzed for changes in blood flow. 
It turns out that many types of bodily substances such as muscle, skin,
and bone are partially transparent to near-infrared light, and so an fNIRS
system can “see” up to 4 cm beneath the surface of the skull, which
is far enough to reach the outer layers of the brain. 

That’s far enough for Birbaumer to run a series
of tests in which locked-in-syndrome sufferers learned to change their thoughts
in a way that would show up on the researcher’s fNIRS system.  Then he asked them yes-or-no questions
that the patient knew the answer to, such as “Were you born in Paris?”
Based on the answers to these test questions, Birbaumer estimates that he can
accurately detect the intended answer from a typical patient about 70% of the
time.  This is not great, but it’s
better than chance.  Admittedly,
the sample size is small (four patients), but it’s a start.

What is most interesting about the study was
the answers to questions that no one has been able to ask a totally locked-in
person before:  “Are you
happy?  Do you love to live?”  Three patients who gave fairly reliable
answers to the questions with known correct responses said yes, they were
happy.  Family members welcomed the
news, probably the first communication they had received from their loved ones
in many months.

This work is remarkable for several
reasons.  First, cracking the lock
on locked-in syndrome would be a blessing for both patients, who must be
immensely frustrated at not being able to communicate, and caregivers and loved
ones, who both have and do not have the patient with them.  Second, because of the relatively
simple equipment needed compared to fMRI, there is reasonable hope that the
technology could either be commercialized, or at least used more widely than in
a few research labs for routine communications with locked-in-syndrome
sufferers.  Fortunately, ALS is a
rare disease, occurring in about 2 out of 100,000 per year.  But by the same token, its rarity makes
it somewhat of an “orphan” disease, meaning that drug companies and
research funders often overlook it in preference to more common diseases.  Its cause is unknown except for a few
cases that can be attributed to genetic factors, although it seems to be more
frequent among players of professional sports. 

The intersection of medical technology and
economics has always been troublesome ethically.  Prior to the modern era, the quality of medical care
received depended mainly on wealth, although even the best physicians of the
1700s could do very little compared to the average general practitioner of
today.  Even in countries with
government-funded single-payer healthcare systems, resources are limited, and
life-or-death decisions about who gets what treatment are sometimes made by
faceless bureaucrats, with sometimes dire personal consequences for those who
don’t make it through the approval process for treatment.  Like the poor that we will always have
with us, there will always be some sick people who cannot be cured, whether for
reasons of economics or limited medical technology.  But devices such as the “mind-reading” fNIRS
system can alleviate the suffering of those whose fate is to be still in this
world, but who cannot respond voluntarily to any human voice or touch.

There is still a role for charitable
organizations in medicine, entities whose primary purpose is not to make money,
but to succor the suffering. 
Perhaps such an organization will undertake to develop the Birbaumer
system into something that can be used more widely by victims of locked-in
syndrome, with appropriate precautions against giving false hopes that would be
disappointed later.  In the
meantime, I hope other fNIRS researchers will follow up this promising lead and
pry open the door that has been closed on locked-in people so far.



Source link