Can the Brain of a Patient in a Coma React to Sounds?

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February 2019 | Volume 7 | Article 19 | 1kids.frontiersin.org
NEUROSCIENCE
Published: 15 February 2019
doi: 10.3389/frym.2019.00019
When people are in comas, they are unconscious and cannot
communicate with their environment. They cannot speak and their
eyes are closed. They look as if they are asleep. However, the brain of
a coma patient may continue to work. It might “hear” the sounds in the
environment, like the footsteps of someone approaching or the voice
of a person speaking. In this article, we will see how we can measure
brain activity in patients who are comatose and how the brains of coma
patients react to sounds. These reactions can inform medical doctors
of whether the patients will awake from the coma.
WHAT HAPPENS WHEN SOMEONE IS IN A COMA?
Imagine a person who has fallen into a coma. A coma can occur from
many causes, such as a traumatic brain injury, a stroke, or maybe loss
of oxygen from a near drowning. The comatose person is lying still
on the bed, with eyes closed. The person does not show any sign of
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CAN THE BRAIN OF A PATIENT IN A COMA REACT TO
SOUNDS?
Athina Tzovara
1
* and Marzia De Lucia
2
1
Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, CA, United States
2
Laboratoire de Recherche en Neuroimagerie, Department of Clinical Neurosciences, Lausanne University Hospital and
University of Lausanne, Lausanne, Switzerland

Tzovara and De Lucia Comatose Patients’ Reactions to Sounds
February 2019 | Volume 7 | Article 19 | 2kids.frontiersin.org
communication with the environment. We speak to the comatose per-
son, but he or she does not respond and seems indierent to everything
that is happening. When a person is in a coma, this person is in what we
call an unconscious state. But is the brain of a coma patient still working?
There is a good chance that the brain of a person in a coma continues
to process events from the environment, for example the footsteps of
someone approaching or the sound of your voice when you speak to
them [1]. To measure the brain activity of a person in a coma, we use
a tool called electroencephalography (EEG). EEG helps us record the
activity of cells in the brain called neurons. We can measure the elec-
trical activity of brain cells by placing electrodes on a person’s head.
These electrodes are inside a cap. Imagine something like a swimming
cap with a lot of holes in it. Electrodes are inserted into these holes and
touch the skin of the scalp. Every time that we see or hear something,
neurons in the brain fire. This firing can change the electrical activity
that we measure on the head with EEG. EEG is used to study the neural
functions of coma patients, because it is easy to use at the patients’
bed without causing any pain or discomfort.
Importantly, EEG can be used to help medical doctors diagnose how
serious a person’s coma is, according to their brain functions. Usually,
coma patients have their eyes closed and cannot see what happens
around them. But their ears keep receiving sounds from the environ-
ment. In some cases, the brains of coma patients can process sounds,
for example the voice of someone speaking to them [2]. Coma patients
may not understand those sounds, and not remember them when they
awake. Still, their brains may receive and process the sounds to some
degree. With EEG, we have the unique opportunity to study whether
the brain of a coma patient responds to sounds, even when this patient
cannot communicate with us. What is really amazing is that by studying
brain responses to sounds, medical doctors can evaluate whether a
patient is likely to awake from the coma and sometimes even determine
what the patient’s neurological condition will be after awakening [3].
STUDYING BRAIN RESPONSES TO SOUNDS, TO PREDICT
WHICH PATIENTS WILL AWAKE FROM A COMA
Let us discuss one cause of coma, decreased oxygen delivery to the
brain. Our brain cells, like all cells, need oxygen to function. Brain cells
receive this oxygen from blood circulating in the brain. If the heart
stops working, no oxygen will reach the brain. It is then common to
lose consciousness and fall into a coma. A treatment for coma patients
is to lower the body temperature in order to protect their brains from
excessive trauma. Patients remain in this decreased body temperature
ELECTROENCEPHA
LOGRAPHY EEG
A tool that helps
clinicians and research-
er to measure the
electric activity pro-
duced by the brain, by
placing electrodes on a
person’s head.

Tzovara and De Lucia Comatose Patients’ Reactions to Sounds
February 2019 | Volume 7 | Article 19 | 3kids.frontiersin.org
for 24 h and then their bodies are rewarmed. Hopefully, patients can
later awake from their comas and regain consciousness.
It is important for medical doctors to have ways of knowing which coma
patients are likely to awake. This information will help them to provide
the best treatment for the patients, and also to inform the patients’
families about the likelihood of recovery. In most hospitals, there are
clinical tests to find out which coma patients are not doing well. But
there are very few tests to predict when a patient will awake, and an
accurate prediction is usually challenging. In our study, we aimed at
developing a test that predicts whether a patient will awake from a
coma. For this test, we studied the brain responses of coma patients
to sounds [4]. We inserted earphones into the patients’ ears and played
sounds to them (Figure 1).
The sounds we played were very short artificial “bips” and we presented
them in a quick and rhythmic way. Imagine, for example, a series of
sounds coming from tapping your fingers repeatedly, or from playing
a musical note on the piano. Imagine listening to the same note being
played over and over again. If this note is replaced all of a sudden with
a dierent note, your brain will show a “surprise” response to the dif-
ferent note, because it is unexpected. In our study, we call the sounds
that are repeated “standard sounds” and the dierent sounds “deviant
sounds.” You can see an example of the sounds in Figure 1, shown in
gray (standard sounds) and yellow (deviant sounds). You can also hear
some of these sounds in Audio File 1. We presented these sounds to
the patients and while we measured their brain activity with EEG. Our
goal was to study how their brains reacted to the series of sounds.
The brain activity that we measure using EEG can be “drawn,” using
dierent colors to create maps (Figure 2). Dierent colors on the maps
show that dierent brain regions were activated in response to sounds.
Brain functions can be dierent from one patient to another. For this
reason, we computed a mathematical model to find patterns in brain
responses to standard or deviant sounds (Figure 1B). We used these
patterns to measure whether the patients’ brains could discriminate
the dierent types of sounds (Figure 1B). We repeated this analysis two
STANDARD SOUNDS
Sounds that are
frequently repeated.
DEVIANT SOUNDS
Dierent sounds from
the standard ones, they
cause a surprise
reaction in the brain.
Figure 1
(A) We presented a
series of sounds to
coma patients. Most of
the time, the sounds
were identical to one
another (standard).
Sometimes, the
standard sound was
replaced by a dierent
sound (deviant). We
measured the brain
responses of coma
patients to every sound
that they heard, by a
tool called electroen-
cephalography. This
allows us to study how
the brain of patients is
reacting to sounds and
whether it can tease
apart standard (gray)
from deviant (yellow)
ones. (B) We grouped
brain responses to
dierent types of
sounds together by
using mathematical
models. The gray and
yellow circles show the
groups of responses to
standard and deviant
sounds. We then used
these groups to
examine whether the
brain of a patient can
discriminate standard
from deviant sounds. Figure 1

Tzovara and De Lucia Comatose Patients’ Reactions to Sounds
February 2019 | Volume 7 | Article 19 | 4kids.frontiersin.org
times, in the first and second day of coma. The first time we measured,
the body temperature of the patients was lowered. The second time, the
temperature was back to normal [5]. We then computed how the ability
of the patients’ brains to tell apart dierent types of sounds changed
from the first to the second day.
EEG AS A WINDOW INTO THE BRAIN OF COMA PATIENTS
All the patients we included in this study were fully unconscious. Their
bodies could not react to most of the things happening around them.
What about their brains? Very interestingly, the brains of several patients
reacted to the sounds that we played to them. Most patients’ brains
exhibited maps with dierent colors, depending on whether the sound
played was standard or deviant. This suggests that the patients’ brains
could tell apart the sounds they heard. This ability to tell dierent sounds
apart was almost as accurate as for healthy and awake people, at least
for the first day of coma. In the second day, the ability to discriminate
sounds was decreased for those patients who later died. This means
that their brains could not easily tell whether a sound was standard or
deviant. Our next question was whether this decreased ability to tell
sounds apart was related to the patient’s outcome.
For each patient, we measured how much the ability of the brain to tell
sounds apart changed, from the first to the second day of coma. Only
patients who later awoke from their comas showed an improvement in
their brains’ ability to discriminate sounds over the 2 days. In Figure 2,
you can see the EEG responses to standard and deviant sounds for
a patient who later awoke. On the second day of coma, the patient’s
Figure 2
We recorded brain
responses from a
patient on the first and
second day of coma.
For each day of coma
you can see the maps
of EEG responses to
standard and deviant
sounds. Each map
shows the
measurement
performed across the
electrodes located on
the head of the patient
in order to uniformly
cover the scalp surface.
Dierent colors
correspond to dierent
values of the electric
activity produced by
the brain and measured
by the EEG. You can
see that, on the first day
of coma, the brain
responses to standard
and deviant sounds
were almost identical to
each other, as they
have similar colors
(blue to the top, red to
the bottom). One the
second day, you can
see that the responses
to standard and deviant
sounds are very
dierent from each
other, and the maps do
not look similar any
more. This means that
the ability of the
patient’s brain to tease
the sounds apart
improved from the first
to the second day of
coma. In our
experiments, we found
that this improvement
means that the patient
is likely to awake from
the coma. Indeed,
some days after our
recordings this patient
awoke. Figure 2

Tzovara and De Lucia Comatose Patients’ Reactions to Sounds
February 2019 | Volume 7 | Article 19 | 5kids.frontiersin.org
brain was able to better discriminate the two types of sounds than on
the first day. A few days later, this patient awoke from the coma. The
patient could communicate with friends and family again.
CONCLUSIONS AND FUTURE WORK
EEG is an exciting tool that gives a window into a person’s brain func-
tions, even when a person cannot communicate with us. Using this
fascinating technique, we found that the brains of coma patients can
react to sounds. Patients themselves were deeply unconscious and
could not perceive what was happening around them. In our study, we
used very simple and artificial sounds. In the future, we could repeat the
experiment using speech or music. We could then examine whether
the brain’s ability to react to speech predicted the chances of a patient
regaining consciousness.
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2. Cossy, N., Tzovara, A., Simonin, A., Rossetti, A. O., and De Lucia, M. 2014.
Robust discrimination between EEG responses to categories of environmental
sounds in early coma.
Front. Psychol
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SUBMITTED: 02 January 2019; ACCEPTED: 28 January 2019;
PUBLISHED ONLINE: 15 February 2019.
EDITED BY: Robert T. Knight, University of California, Berkeley, United States
CITATION: Tzovara A and De Lucia M (2019) Can the Brain of a Patient in a Coma
React to Sounds? Front. Young Minds 7:19. doi: 10.3389/frym.2019.00019

Tzovara and De Lucia Comatose Patients’ Reactions to Sounds
February 2019 | Volume 7 | Article 19 | 6kids.frontiersin.org
CONFLICT OF INTEREST STATEMENT: AT and MD are listed as inventors in a US
patent entitled: “Method for predicting awakening in a comatose patient and com-
puter-implemented method thereof” (application number: 14/383165). The patent
is owned by Lausanne University Hospital and is currently not licensed.
COPYRIGHT © 2019 Tzovara and De Lucia. This is an open-access article distrib-
uted under the terms of the Creative Commons Attribution License (CC BY). The
use, distribution or reproduction in other forums is permitted, provided the original
author(s) and the copyright owner(s) are credited and that the original publication
in this journal is cited, in accordance with accepted academic practice. No use,
distribution or reproduction is permitted which does not comply with these terms.
YOUNG REVIEWERS
FLORIMONT, AGES: 15-16
In our group of reviewers, we had a great atmosphere. Everyone worked well together.
We laughed a lot during the review on the article on comas.
AUTHORS
ATHINA TZOVARA
I am a Neuroscientist using computational techniques to study functions of the human
brain. I am interested in consciousness and how the brain processes stimuli from
the environment according to our levels of attention or awareness. I am currently
working at the University of California, Berkeley, in the USA. *athina.tz@gmail.com
MARZIA DE LUCIA
I am a Researcher interested in brain functions that remain preserved when con-
sciousness fades away, such as during coma or disorders of consciousness. I work
at the University Hospital in Lausanne and I collaborate closely with other hospitals
in Switzerland, in order to gather datasets from dierent clinical settings.