13 June 2011

Consciousness and Frontiers in Brain Imaging:

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 second.

An "electronic scan" is thus 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, thus tracking the brain's processing activity. _SD
EIT Images in Six Subjects

Researchers at the University of Manchester have created 3-D images of the brain in the act of losing consciousness. They were using a relatively new brain imaging technique called functional Electrical Impedance Tomography (fEIT). fEIT can measure brain electrical activity directly with a rapid time resolution in milliseconds.

More on the study from U. of Manchester:
Brian Pollard, Professor of Anaesthesia at The University of Manchester (UK), will tell the European Anaesthesiology Congress in Amsterdam 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.
"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," said Prof Pollard.

..."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. 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 teams investigating electrical impedance tomography (EIT), but this is its first application to anaesthesia. Prof 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. 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 _SD

This new functional brain imaging technology has the potential for scaling to rather small, portable machines, suitable for use in a wide range of locations and situations. While temporal resolution is excellent, spatial resolution will require a lot of improvement if the tool is to be used as a diagnostic or screening device, beyond the current role in research.

From Wellcome.ac.uk: "Functional brain imaging is now an essential tool, and is well established in medicine.

The need for brain imaging is increasing with growing concern over neurodegenerative diseases, such as Alzheimer's; hence there are larger numbers of patients to be routinely scanned than ever before. Current scanners are not available in every hospital due to their high cost. Where they are available they are large, noisy, fixed installations that are not portable. Professor Hugh McCann and Dr Chris Pomfrett from the University of Manchester have been awarded translational funding to develop a newly discovered technique called 'functional electrical impedance tomography of evoked responses' (fEITER), which is directly sensitive to the brains electrical operation. This tool will enable screening of large populations, and prompt action to be taken in emergencies. The scans could be performed wherever the patient is, even at home. _Wellcome.ac.uk"

With the rapid aging of populations in the more developed world and in emerging nations, the need for such a portable screening tool for dementia and other neurodegenerative diseases should be obvious. In the lab, it is very likely that exciting new research tools of this type will make large numbers of startling discoveries about what makes our brains tick. In the ICU and Emergency Department, rapid screening for acute catastrophic brain events will prove life-saving. Once perfected, even ambulance crews may carry future generations of such devices.

As for the main story above: the brain being caught in the act of losing consciousness by fEIT? To make the most of such research, better spatial resolution will be needed.


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