X-Message-Number: 12906
Date: Mon, 06 Dec 1999 21:01:49 -0500
From: Jan Coetzee <>
Subject: Determining PVS
Determining a Diagnosis
for Persistent Vegetative
State
by Pete Moore
Determining whether someone is truly in a
persistent vegetative state (PVS) can be a life
or death issue. The UK court s landmark
decision to allow food and water to be
withdrawn from football supporter Tony Bland
who was in PVS for three years after being
crushed in the 1989 Hillsborough football
disaster, highlights the need for accurate
diagnosis. However, there is no agreement
about a definition of PVS.
At the Society for Neuroscience meeting in
Miami, USA, researchers from the UK presented
new functional imaging data from three patients
who had been diagnosed as being in PVS, which
showed that two of them had residual cognitive
function. These two patients went on to make
fairly successful recoveries. The third patient
showed no cognitive responses and has never
recovered consciousness.
Watching a relative or friend lie in a hospital
bed
day after day making no discernable response to
any stimulation is traumatic. But the situation is
exacerbated because current measures of brain
function are still so crude that no-one can say
definitely whether the patient has any residual
consciousness or whether they are effectively
dead.
Neuroscientist, Adrian Owen, together with
consultant Anesthetist David Menon and
colleagues from the University of Cambridge, UK,
have set out to see whether functional imaging
of the brain can be used to detect
consciousness. Their hope is that if so, this
could become a valuable tool in diagnosing a
patient s true condition.
Owen presented data from three patients. One
was a female who fell into a coma after having a
severe fever. We set out to see whether her
cortex could respond to faces of people that she
knew, in much the same way that would occur in
a normal healthy awake individual, explains
Owen.
To do this, they used photographs of faces of her
friends and family and a set of controlled images
where the faces were scrambled so that they had
the same color content and brightness as the
photos, but no facial information. The patient
was shown the photos six times, for 12 seconds
on each occasion, while having her brain scanned
using a 15-oxygen PET scanning technique. She
was also shown the control images on six
occasions.
Using standard subtraction analyses the team
found that seeing the photographs caused a very
specific activation of the right fusiform gyrus
(BA
37), an area commonly referred to as the face
area. The patient appeared to be recognizing the
image, even though she was incapable of making
any response.
The second patient they looked at had suffered
from a traffic accident and appeared to be
cortically blind, as giving visual stimuli failed
to
elicit any electroencephalograhic response. So
this time the team played recordings of voices or
white noise while she was having her brain
scanned. This time we saw activation of the
superior temporal gyrus in both hemispheres, a
response that we also found in normal healthy
volunteers, says Owen.
Both of these patients went on to make an
almost complete cognitive recovery but
unfortunately the third patient, who was in a
coma following a high fever, failed to show any
functional responses to stimuli and has never
shown any signs of regaining consciousness.
Owen explains that for these tests to be
significant one needs to use stimulus that is
known to affect a specific area of the brain;
Contrary to popular perception there are only a
few well mapped-out regions of the brain -- face
perception is one and speech recognition is
another . He adds that interpreting the
information can be quite difficult if the brain is
physically distorted: you just can t make sense
of the scan information.
The Cambridge team are currently repeating this
work using Magnetic Resonance Imaging, in order
to avoid the radiation burden caused by PET.
This will enable them to perform multiple studies
on an individual and look for responses from
more than one stimulus. They are also planing to
look to see whether anaesthetized people show
any speech recognition.
Our goal would be to be able to use functional
imaging to predict outcome. I would certainly
like to see fMRI applied to patients in PVS as
well as patients in related conditions, such as
locked in syndrome, says Owen.
Editor's choice links
Evidence for a two-stage model of spatial
working memory processing within the lateral
frontal cortex: a positron emission tomography
study.
Owen AM, Evans AC, Petrides M
Cereb Cortex 1996 Jan-Feb 6:1 31-8 [MEDLINE],
[full MEDLINE], [related records], [cited by]
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