Thursday, December 8, 2011

Tilt The Head To Pick Up Brainwaves

Getting a more accurate picture of someone's brainwaves could simply be a case of lying them down. The boost this gives to the electrical signals that can be read from the brain could improve diagnosis of brain disorders and enhance control of brain-machine interfaces.
 Electroencephalography, or EEG, is a relatively cheap, non-invasive way to measure brain activity using a cap of electrodes. But the signal it picks up can be weak, as it must pass through a layer of cerebrospinal fluid (CSF) and the skull before it reaches the scalp and electrodes. It was assumed that the skull was the biggest obstacle in the signal's path. But Justin Rice at The City College of New York wondered whether the depth of the CSF might also be a problem. To investigate, one member of his team took 16 MRI images of his own brain. For half of the scans, he lay on his back, while in the other half he lay on his stomach. As suspected, the brain shifted slightly with gravity.
"The brain is heavy — it's going to move up and down," says Rice. What's more, the depth of the CSF layer changed depending on the researcher's position. "There was an average 1.55 millimetre difference in the thickness" between facing up and down, says Rice. The group then used EEG to monitor the brain activity of 14 volunteers as they carried out five visual tasks. Each repeated the task three times — once sitting down, once lying on their back and once lying on their front. Because the visual cortex is at the back of the brain, Rice's group expected to see a stronger signal when each person was lying on their back — allowing the brain to drop towards the back of the skull, thinning the CSF layer here. Sure enough, in four of the five tasks, this position boosted the EEG signal by around 30 per cent. In the fifth task, the signal was up to 200 per cent stronger. Rice presented the work at the Society for Neuroscience annual meeting in Washington DC in November.
CSF appears to have an impact on the signal because of its conductivity. "The current takes the path of least resistance, [moving laterally] through the CSF rather than the skull," says Rice. A thinner CSF layer means that more current reaches the skull, creating a stronger signal. The simplicity of head-tilting is likely to make it an attractive option. "People buy huge copper rooms to limit interference with the signal, and they cost hundreds of thousands of dollars," Rice says. This is much more cost effective." The discovery should be taken into account by clinicians, too, says Rice.
"With neurodegeneration or just normal ageing, the brain shrinks, resulting in a thicker layer of CSF," he says. "This could result in a weaker EEG signal!' Enhanced signals could also be useful in brain-machine interfaces that allow people to move robotic limbs or wheelchairs by thought alone. The same is true for thought-controlled computer games. Jonas Obleser, a neuroscientist at the Max Planck Institute for Human and Cognitive Brain Sciences in Leipzig, Germany, says the findings are a "worthwhile and creative demonstration".



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