How does complex behavior spontaneously emerge in the brain?

The idea of emergence, in which complex behavior spontaneously emerges out of simple interactions, exists in a wide variety of areas, such as economics, the Internet, and urban development. But perhaps the ultimate example of emergence is in the brain, where thousands of randomly firing neurons spontaneously reach a coherent state of collective, periodic firing that underlies all brain functions. Despite significant progress, the mechanisms responsible for the origin and maintenance of spontaneous neuronal activity are still poorly understood.

In a new study published in Nature Physics, a team of researchers from Spain has shown that emergence in neuronal networks can be explained as a noise-driven phenomenon that is controlled by the interplay between network topology and intrinsic neuronal dynamics. In this scenario, a randomly fired pulse propagates through the network and is amplified by noise focusing, which the researchers describe as an implosive concentration of spontaneous activity.

"From the experimental point of view, we show that in neuronal cultures, the emergence early in the development of collective spontaneous activity is dominated by the presence of activity waves that initiate in specific regions of the culture, in a similar way as it happens in vivo," lead author Javier G. Orlandi at the University of Barcelona told Phys.org. "And with the help of simulations, we also show that you don't need any special mechanism to explain this behavior, just the right combination of network structure and dynamics. These waves emerge naturally from the noise focusing effect, in which individual firings propagate and concentrate in specific regions to later generate these activity waves."