Physicists at the Universities of Bonn and Oldenburg have developed a model whose behavior – although based on strict rules – can apparently change spontaneously. There are also changes of this type in nature, for example, in the development of migraine attacks or epileptic seizures. The mechanism, described for the first time by the researchers, could help to better understand extreme events such as these. The work will be published soon in the professional journal "Physical Review X", and it is already available online.
Irregular fiery red rings move across the computer screen. They enlarge, merge together, dissipate, form offspring – a constant cycle of emergence and decay. But suddenly the screen grows dark; the rings have disappeared. For a few seconds, nothing happens.
Then the dark surface begins to pulsate. It rhythmically changes its color, almost imperceptibly at first but this becomes clearer. Shortly thereafter there is a second change: The entire surface suddenly flashes red. Finally, the rings reappear; the extreme event is over.
Something similar may appear in the brain when a migraine attack begins or an epileptic seizure develops: Suddenly, billions of neurons simultaneously enter an exceptional state. The rules which they normally obey appear to be overridden all at once.
The software depicting its results on the computer screen in the office of the Department of Epileptology at the University of Bonn Hospital shows very similar behavior: Seemingly out of nowhere, at completely unpredictable intervals, the underlying model changes its dynamics. What is astonishing is that it actually obeys simple rules which nonetheless create a kind of randomness.
This model is a network of many thousands of individual elements, the nodes. These are interconnected – they can thus communicate with and influence each other. In this process, they interact not only with their neighbors but also with some remote nodes. Scientists refer to a "small-world" network. Nerve cells in the brain communicate with each other in a very similar way.
Although the rules of communication are precisely determined, networks of this type demonstrate a very complex behavior. On the one hand, this is due to the multitude of nodes, and on the other hand due to the wiring connecting these nodes. "We have now been able to show that the behavior of such networks can spontaneously change," explains Gerrit Ansmann, lead author of the work and doctoral candidate in the Neurophysics group.
"However, these changes only occur under certain conditions," explains Prof. Dr. Klaus Lehnertz, head of the group. "We hope, with our model, to be able to better understand the conditions under which extreme events develop in the brain."
The switching between various patterns of activity including the generation and termination of extreme events is based on a fundamental mechanism, which can also be translated to other system, e.g. to patterns of excitation in the heart. “This generality allows for broad applications of our findings in other scientific fields”, underlines Prof. Dr. Ulrike Feudel, head of the group Theoretical Physics/Complex Systems at the Institute for Chemistry and Biology of the Marine Environment of the University of Oldenburg.
The work is part of a project funded by the Volkswagen foundation. In this project, the scientists investigate the mechanisms through which extreme events develop using the examples of epileptic seizures and toxic algal blooms.
Publication: Gerrit Ansmann, Klaus Lehnertz and Ulrike Feudel: Self-induced switchings between multiple space–time patterns on complex networks of excitable units
Media contact information:
Prof. Dr. Klaus Lehnertz
Department of Epileptology
University of Bonn Hospital
Prof. Dr. Ulrike Feudel
Theoretical Physics/Complex Systems
Institute for Chemistry and Biology of the Marine Environment
Carl von Ossietzky University Oldenburg
http://arxiv.org/abs/1602.02177 Publication online
Johannes Seiler | idw - Informationsdienst Wissenschaft
Gamma rays will reach beyond the limits of light
23.10.2017 | Chalmers University of Technology
Creation of coherent states in molecules by incoherent electrons
23.10.2017 | Tata Institute of Fundamental Research
Salmonellae are dangerous pathogens that enter the body via contaminated food and can cause severe infections. But these bacteria are also known to target...
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
23.10.2017 | Event News
17.10.2017 | Event News
10.10.2017 | Event News
23.10.2017 | Life Sciences
23.10.2017 | Physics and Astronomy
23.10.2017 | Health and Medicine