In a nutshell: Previously unidentified class of electrical activity found in the unconscious brain.

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The Big Picture:

Brain states such as sleep and anaesthesia are characterised by slow changes in brain electrical activity. These slow waves were thought to indicate low levels of activity, like the slow rise and fall of the ocean on a calm day.

Now CIBF investigators Pulin Gong and Paul Martin, and colleagues at University of Sydney and University College London, have shown that even unconscious brains may be very active indeed.

When they measured the fine detail of electrical activity of the brain’s visual centres in anaesthetised monkeys, they found the slow waves actually hide a previously unidentified class of brain electrical activity: a rich variety of micro-patterns, just 4 mm across, that evolve continuously in space and time.

“These micro-patterns were not at all like a calm sea,” says Martin. “In fact the pictures we got were more like a series of tropical storms.” According to Martin, the micro-patterns morph and move rapidly, at rates similar to those seen in electrical activity associated with conscious processing of vision, touch and hearing, and physical activity, not with anaesthesia or sleep.

To make sense of the patterns, physicists in the team applied methods for analysing turbulent flow in gas and fluids. When you experience air turbulence on a bumpy flight it can feel that the bumps are random. In fact, there are hidden patterns in turbulence, and physics has special mathematical tools to analyse them.

“We modified the equations and applied them to the micro-patterns, and the fit was excellent,” says lead author Rory Townsend, a CIBF graduate student.

The team speculate that information may be encoded in the micro-patterns, communicated by their movement, and processed when they interact.

Next steps:
A first step will be to eliminate the possibility that the micro-patterns are an artificial byproduct of anaesthesia. This team and others will also investigate what influence the micro-patterns have on “spiking activity” in nerve cells, which is already known to encode information for communication between brain regions, and to control physical movement and other functions.

Townsend, R. G., Solomon, S. S., Chen, S. C., Pietersen, A. N., Martin, P. R., Solomon, S. G., & Gong, P. (2015). Emergence of complex wave patterns in primate cerebral cortex. The Journal of Neuroscience, 35(11), 4657-4662.

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