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Conscious decisions

Since modern anaesthesia was first employed 171 years ago to lessen the pain of surgery, the true nature of human consciousness and unconsciousness has remained a scientific mystery. Now, armed with one of the world’s most advanced diagnostic instruments and the rarest naturally occurring gas, a team of Australian scientists are proposing to reveal the way our brain activity is transformed when we descend into unconsciousness.

Impelled by media horror stories of patients ‘awake under the knife’ and by resulting insurance claims and psychological trauma, a 30-year global research effort has so far failed to disclose exactly how anaesthetic drugs act upon the brain, the mind and the state of consciousness – despite the millions of operations performed with them around the world every day.

Defining the nature of consciousness

For Swinburne’s Professor David Liley, the nature of consciousness has been a lifetime fascination, marked by an important milestone in 2012 when his Brain Anaesthesia Response (BAR) device entered clinical trials as a potential replacement for existing electroencephalogram techniques used the world over to monitor patients under anaesthetic. Now, in a world-first experiment in partnership with Melbourne’s St Vincent’s Hospital, Professor Liley and a talented team of intrepid ‘brain geographers’ are combining the power of magnetoencephalography (MEG) – reading minute electromagnetic signals within the brain – with the use of a rare and costly anaesthetic, the noble gas xenon, to try to define the process that takes place when a person passes from one state of consciousness to another.

“Despite all the monitoring of brain function that has gone on over the years, consciousness remains a black box,” he explains. “We have huge amounts of data about brain states, but little or no insight into the thing we are really trying to monitor: whether a person is conscious or unconscious. Whether they are aware of what is happening around them, or can feel pain.”

New technology and the volunteer study

Equipped with one of only two MEG machines in Australia, Professor Liley and his colleagues at Swinburne’s Brain and Psychological Sciences Research Centre are studying electromagnetic signals many millions of times weaker than the earth’s magnetic field. This is a task of such exquisite delicacy it must be carried out in a specially shielded chamber that excludes all extraneous magnetic signals. A special gantry holds a helmet with 306 sensors over the patient’s head, monitoring the tiny electromagnetic fluctuations produced by populations of neurons while they communicate with one another, to sensitively assay brain activity as the patient passes under the influence of the anaesthetic.

Twenty volunteers will take part in the study, equipped with a mask for administering the gas mixture and provided with a simple low-attention task – pushing a button in response to a tone – to compare their reactions with those revealed by the MEG machine as it monitors the changing signals in their brain.

“We are using xenon and nitrous oxide gases as our chosen anaesthetics as they are both widely believed to work by the same essential mechanism, reducing brain excitation, but so far have been reported to produce quite different effects on brain activity. However, we have good reasons to hypothesise they both impact a particular part of the brain – the parietal lobe – and that this represents the common pathway into unconsciousness. If this turns out not to be the case it might mean that there is no single route to unconsciousness,” Professor Liley explains. “Thus our experiment will provide important insights into the process by which consciousness is maintained or lost, and where in the brain this occurs. We will start with the patient fully awake and record the changes in brain electromagnetic activity as they become sedated and lose and regain consciousness.”

Multiple applications and lower risks

While Professor Liley’s research will not attempt to cast light on the nature of consciousness, it has every chance of revealing the actual physical steps and changes involved. The research outcomes could contribute to the development of new ways to monitor the brain state of anaesthetised surgical patients, people in comas and people suspected of early-onset mental diseases such as Alzheimer’s or Parkinson’s. The research will also provide insights that could assist in the design of new and better anaesthetics, avoiding the risk of ‘awakening’ or other side effects.

“In this research our ideal aim is to define the processes or steps which invariably occur, under all forms of anaesthesia, as the state of consciousness changes,” Professor Liley says.

“If we can better understand the mechanisms of consciousness, we can make sure patients are genuinely 100 per cent unconscious when they are supposed to be. We will also have a valuable new diagnostic tool for exploring other central nervous system conditions.”

Xenon: in its element

Xenon is a colourless, odourless noble gas, meaning it is so inert, it does not react with other chemicals to form compounds. It occurs in the earth’s atmosphere at a ratio of about one part in 11,500,000. Its main uses are in arc lamps, lasers and, since the 1950s, as a surgical anaesthetic.

Produced by filtering air, xenon is expensive – more than three times the price of standard chemical anaesthetics. Its high cost has limited its use in medicine but recent advances in recovery methods have increased its affordability. Currently it is only approved for routine anaesthetic use in Europe.

“Xenon is a remarkable element,” says Professor Liley. “It is completely unreactive with other chemicals in its surrounding environment, and yet it produces a profound anaesthesia. This makes it ideal for modelling the process of loss of consciousness.”