3-D movie shows what happens in the brain as it loses consciousness
Brian Pollard, Consultant at the MRI and Professor of
Anaesthesia at Manchester Medical School, told the European
Anaesthesiology Congress in Amsterdam last week that the real-time
3-D images seemed to show that losing consciousness involves a
change in electrical activity deep within the brain, changing the
activity of certain groups of nerve cells (neurons) and hindering
communication between different parts of the brain.
He said the findings appear to support a hypothesis put forward
by Professor Susan Greenfield, of the University of Oxford, about
the nature of consciousness itself. Prof Greenfield suggests
consciousness is formed by different groups of brain cells (neural
assemblies), which work efficiently together, or not, depending on
the available sensory stimulations, and that consciousness is not
an all-or-none state but more like a dimmer switch, changing
according to growth, mood or drugs. When someone is anaesthetised
it appears that small neural assemblies either work less well
together or inhibit communication with other neural assemblies.
Professor Pollard said: "Our findings suggest that
unconsciousness may be the increase of inhibitory assemblies across
the brain's cortex. These findings lend support to Greenfield's
hypothesis of neural assemblies forming consciousness."
The team use an entirely new imaging method called "functional
electrical impedance tomography by evoked response" (fEITER), which
enables high-speed imaging and monitoring of electrical activity
deep within the brain and is designed to enable researchers to
measure brain function.
The new device was developed by a multidisciplinary team drawn
from the Schools of Medicine and Electrical and Electronic
Engineering at The University of Manchester, led by Professor Hugh
McCann and with support from a Wellcome Trust Translation
The machine itself is a portable, light-weight monitor, which
can fit on a small trolley. It has 32 electrodes that are fitted
around the patient's head. A small, high-frequency electric current
(too small to be felt or have any effect) is passed between two of
the electrodes, and the voltages between other pairs of electrodes
are measured in a process that takes less than one-thousandth of a
An 'electronic scan' is therefore carried out and the machine
does this whole procedure 100 times a second. By measuring the
resistance to current flow (electrical impedance), a
cross-sectional image of the changing electrical conductivity
within the brain is constructed. This is thought to reflect the
amount of electrical activity in different parts of the brain. The
speed of the response of fEITER is such that the evoked response of
the brain to external stimuli, such as an anaesthetic drug, can be
captured in rapid succession as different parts of the brain
respond, so tracking the brain's processing activity.
"We have looked at 20 healthy volunteers and are now looking at
20 anaesthetised patients scheduled for surgery," said Professor
Pollard. "We are able to see 3-D images of the brain's conductivity
change, and those where the patient is becoming anaesthetised are
"We have been able to see a real time loss of consciousness in
anatomically distinct regions of the brain for the first time. We
are currently working on trying to interpret the changes that we
have observed, as we still do not know exactly what happens within
the brain as unconsciousness occurs, but this is another step in
the direction of understanding the brain and its functions."
The team at Manchester is one of many worldwide investigating
electrical impedance tomography (EIT), but this is its first
application to anaesthesia. Professor Pollard said that a huge
amount of research still needed to be done to fully understand the
role EIT could play in medicine.
"If its power can be harnessed, then it has the potential to
make a huge impact on many areas of imaging in medicine," he said.
"It should help us to better understand anaesthesia, sedation and
unconsciousness, although its place in medicine is more likely to
be in diagnosing changes to the brain that occur as a result of,
for example, head injury, stroke and dementia.
"The biggest hurdle is working out what we are seeing and
exactly what it means, and this will be an ongoing challenge."
Notes for editors
Professor Pollard's presentation at the European Anaesthesiology
Congress took place on Saturday, June 11, at 15:15 hrs (CEST),
abstract no: 7AP1-6.
Pictures of the images produced by fEITER are available for
journalists to use.
Euroanaesthesia 2011, the European Anaesthesiology Congress, is
taking place from June 11-14 at the Amsterdam RAI Convention Centre
(Amsterdam, The Netherlands). A total of 847 abstracts will be
presented at the Congress, and 5,500-6,000 delegates from more than
90 countries around the world will be attending.
For further information contact:
Central Manchester University Hospitals NHS Foundation Trust
Tel: 0161 276 6937
Or Aeron Haworth
Faculty of Medical and Human Sciences
The University of Manchester
Tel: 0161 275 8383
Mob: 07717 881563