How does complex behavior spontaneously emerge in the brain?

August 26, 2013 by Lisa Zyga, feature

A spatial representation of the background avalanche activity in a circular culture with a 2.5-mm radius and density of 300 neurons per mm. Only the top 1% of the most active connections is shown. Different colors correspond to different neuron communities, according to a community detection algorithm. Credit: Javier G. Orlandi, et al. ©2013 Macmillan Publishers Limited
( —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 can be explained as a noise-driven phenomenon that is controlled by the interplay between network topology and intrinsic . 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 "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 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."

The researchers arrived at this explanation by combining high-resolution calcium imaging experiments of rat with simulations. The experiments revealed that bursts of neuronal pulses are controlled by waves that originate at small areas called nucleation sites.

Although previous research has hinted at the existence of such waves, this study is the first that provides sufficiently high resolution to measure the wave velocity for the first time. The random nature of the wave initiation from spontaneous neuronal firing also supports the idea that it is a noise-driven phenomenon, in which the waves are later amplified to become global bursts.

The view of emergence in neural networks as a noise-driven phenomenon differs from the common view in which the bursts of neuronal pulses are controlled by specific leader neurons assisted by the network architecture. In the noise-driven explanation, the nucleation sites do not actively initiate the firing process, but collect and amplify the firing activity that originated elsewhere.

As the researchers explain, understanding the full implications of noise focusing in the brain remains a question for future research.

"The mechanism of noise focusing emerges naturally in any system with interconnected integrate-and-fire units (like neurons), so its effect should also be present in the brain," Orlandi said. "If this effect is important in the brain, or by contrast, if the brain has other mechanisms to counter its effect, is still an open question. It could be that noise focusing is responsible for the generation of waves of activity during development, like in the retina, and that it helps the maturation of specific neuronal pathways."

In the future, the researchers plan to further investigate neuronal activity through more in-depth investigations.

"We want to see what happens in more complex neuronal systems, like slices or electrode recordings from anaesthetized animals, and see if we find the same effect in there," Orlandi said. "We know that activity waves are present in these systems, but we still need to see how these waves form exactly, if it is also due to noise focusing or due to something else. It would also be extremely interesting to check what role noise focusing plays in social networks, for example in rumor spreading."

In this analogy, the points of a rumor's origins can be compared to the nucleation sites where waves originate, and the spreading of a rumor to the brain's collective neuronal firing.

Explore further: Coherence activity in neuronal cultures from noise focusing

More information: Javier G. Orlandi, et al. "Noise focusing and the emergence of coherent activity in neuronal cultures." Nature Physics. DOI: 10.1038/NPHYS2686

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1.4 / 5 (9) Aug 26, 2013
In my model for the adaptive evolution of the brain and behavior, epigenetic effects of sensory input alter intracellular signaling and internuclear interactions that enable seemingly futile thermodynamically controlled cycles of nutrient-dependent protein biosynthesis, and protein degradation to species-specific pheromones that control reproduction in species from microbes to man. For example, in mammals the epigenetic effects of food odors and pheromones are not random, but are instead pulsed through interactive vertebrate neuronal systems that feedback on the gonadotropin releasing hormone-neuronal (GnRH) system, which is directly effected by food odors and pheromones. Thus, the required reciprocity to get from genes to hormone-driven behaviors and back to gene activation (e.g., in GnRH secreting nerve cells of tissue in the brain) represents the ultimate in non-random cause and effect, since it is driven by nutrients and controlled by their metabolism to pheromones.
1 / 5 (4) Aug 26, 2013
The form of noise is unspecified in the article. Chaotic bifurcation can generate pink noise which is observed in nervous systems. The gain can vary to control bifurcation from zero to infinite, which in turn opens the sensitivity of the neural circuit from localized to open, or some would say 'extraverted'
1.8 / 5 (10) Aug 26, 2013
The stone in the pond scenario does nothing to address the requirement that information be pulsed through networks so that greater complexity can arise. Sir Paul Nurse noted that Morse Code can be used to transmit the works of Shakespeare through interconnected networks. Ripples in a pond seem comparatively linear and lack the interconnectivity.
3.7 / 5 (3) Aug 31, 2013
Oh, "epigenetics" crackpottery now? Wasn't 'everything is pheromones' enough buzz words?

It is annoying that this science news site wants to amp its web activity by not prohibiting pseudoscience personal theories, antiscience trolling et cetera. Sort of "science, but not only science". :-/
1.5 / 5 (8) Sep 01, 2013
The structure of the GnRH molecule is thermodynamically stable and conserved across species to the degree that nutrient-dependent pheromone-controlled adaptive evolution is epigenetically effected via the same molecular mechanisms in species from microbes to man. Is that what you are inferring is "epigenetics" crackpottery you under-informed scientific illiterate?
1 / 5 (12) Sep 01, 2013
Is that what you are inferring is "epigenetics" crackpottery you under-informed scientific illiterate?

I do believe that the proper word for your assertion is imply.

So much for your personal level of literacy...
2.3 / 5 (3) Sep 01, 2013
Your last sentence should not have ended with an ellipsis. Nice try Noumenon, but you'd think you would have realized by now you are in no position to criticize people on their use of language. You think "racists" is an adjective for Christ's sake.
0.6 / 5 (19) Sep 01, 2013
Your last sentence should not have ended with an ellipsis. Nice try Noumenon, but you'd think you would have realized by now you are in no position to criticize people on their use of language. You think "racists" is an adjective for Christ's sake.

I didn't make that post. I post under the name "Noumenon", so what are you talking about? I think 'racists' is an adjective? What?

Why would you spend time trying to guess who is who when everyone uses a pseudonym and is therefore anonymous in any case?
not rated yet Sep 12, 2013
How does complex behavior spontaneously emerge in the brain?

in asswipes like Kiwini, it doesn't.

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