The fractal properties of brain activity are part of a bigger picture


In a nutshell: In the primate visual system, fractal-like patterns of activity are found in brain cells that help to detect danger.

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The fractal properties of brain activity are part of a bigger picture

The brain processes information by sending electrical signals between cells. The patterns of electrical activity – also called spike patterns – change depending on the type of brain cells involved and what function the brain is performing at the time.

It is now known that the spike patterns of individual cells can have a fractal quality – that is, they have similar properties whether you zoom in to look at a specific detail or zoom out to look at a much larger scale. Fractal patterns are common in nature – just think of the patterns in snowflakes, clouds, or Romanesco broccoli – and recent discoveries show that they might also be an important part of brain activity.

To understand why fractal-like patterns are important, Brain Function CoE researchers, led by Pulin Gong and Paul Martin at the University of Sydney, analysed cells in the early visual system – the parts of the brain involved in processing visual information.

They measured the spike patterns of single cells from two vision-related areas of the brain in marmoset monkeys: the lateral geniculate nucleus (LGN) and the medial temporal visual cortex (MT). Then, they analysed the patterns using methods that they had developed to detect the statistical fingerprints of fractal activity.

The LGN is made up of three cell types. M-cells are involved in perceiving movement and depth. P-cells have a role in sharp vision. There are different kinds of K-cells; some respond to flashing or moving stimuli, possibly helping us to respond rapidly to nearby threats.

The researchers’ analysis showed that K-cells had more fractal-like spike patterns than P-cells or M-cells. And the spike patterns of MT cells were even more fractal-like than those of K-cells.

“Fractal brain activity is more flexible than constant brain activity, especially in an unpredictable environment”, explains Pulin Gong. The researchers believe that the fractal quality of spike patterns may enable brain activity to change efficiently in response to irregular threats in the animal’s environment, such as the sudden appearance of predators.

Next steps:
The researchers will investigate whether cells in the brains of conscious humans have spike patterns with the same fractal properties.

Munn, B., Zeater, N., Pietersen, A. N., Solomon, S. G., Cheong, S. K., Paul R. Martin, P. R., & Gong, P. (2020). Fractal spike dynamics and neuronal coupling in the primate visual system. Journal of Physiology 598(8), 1551–1571. doi: 10.1113/JP278935

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