Neurons are not randomly arranged in the human brain. In the cortex, they are organized in interconnected clusters with high intrinsic connectivity. This modular connectivity structure, in which clusters eventually serve as functional units, is formed in early phases of development.
The underlying self-organization process is regulated by neuronal activity but the detailed mechanisms are still poorly understood. Based on in vitro studies and computational modeling, neuroscientists Dr. Samora Okujeni and Prof. Dr. Ulrich Egert from the Bernstein Center Freiburg now made an important contribution to the understanding of brain networks and their development: in their current study, they show how neuronal outgrowth and migration interact in shaping network architecture and the degree of modularity in mature networks. Their findings have now been published in the open access online journal eLife.
Neurons are sociable cells that, on the long run, die in isolation. During development, they therefore grow out cellular processes, termed neurites, to establish synaptic connections with other neurons. Once they receive sufficient or too much synaptic input, however, they stop growing or shrink. By this, neurons avoid long-term over-excitation. It is widely assumed among researchers that neuronal growth is hereby controlled to stabilize neuronal activity at a specific target level.
Yet, to increase the probability of connections, neurons cannot only grow out their neurites but are also able to migrate towards other neurons. "In computer simulations we show that migration and neurite outgrowth may interact to shape specific mesoscale network architectures" says Samora Okujeni.
The interaction regulates the relation between local connectivity within clusters and long-range inter-cluster connectivity and thereby the degree of network modularity. "This, in turn, influences the generation and spatiotemporal patterns of spontaneous activity." Such interdependencies may be crucial for the proper development of the cortex.
The scientists tested the model predictions experimentally by investigating how cell migration, neurite outgrowth and activity interact in developing networks of cultured rat cortical neurons. To modulate cell migration in these networks they manipulated an enzyme that is centrally involved in the regulation of the neuronal cytoskeleton. As in their simulations, cell migration and clustering likewise promoted modular connectivity in vitro.
Yet, in addition, clustering promoted activity generation and led to higher activity levels. This was inconsistent with the assumed regulation of growth to establish a common target activity level.
The scientists could resolve this discrepancy: "Cytoskeletal dynamics are not directly controlled by action potential activity but indirectly through an associated calcium influx that influences the balance between growth and degradation." Okujeni explains.
"Modularity increased the overall rate of action potentials but decreased their synchronization across the network that effectively determines the calcium influx per action potential. Given this dependence, we estimated that all network structures attain a similar target level of calcium influx during development."
Okujeni, S., Egert, U. (2019). Self-organization of modular network architecture by activity-dependent neuronal migration and outgrowth.
Elife 8. DOI: 10.7554/eLife.47996
Learn more about Samora Okujeni's work
Bernstein Center Freiburg
Phone: +49 (0)761/203 - 7523
Dr. Samora Okujeni | EurekAlert!
Research against the corona virus - tissue models for rapid drug testing
08.04.2020 | Fraunhofer-Institut für Silicatforschung ISC
Impulse for Research on Fungi
08.04.2020 | Julius-Maximilians-Universität Würzburg
Published by Marc Tudela, Laura Becerra-Fajardo, Aracelys García-Moreno, Jesus Minguillon and Antoni Ivorra, in Access, the journal of the Institute of Electrical and Electronics Engineers
The project Electronic AXONs: wireless microstimulators based on electronic rectification of epidermically applied currents (eAXON, 2017-2022), funded by a...
The Belle II experiment has been collecting data from physical measurements for about one year. After several years of rebuilding work, both the SuperKEKB electron–positron accelerator and the Belle II detector have been improved compared with their predecessors in order to achieve a 40-fold higher data rate.
Scientists at 12 institutes in Germany are involved in constructing and operating the detector, developing evaluation algorithms, and analyzing the data.
Electrolytes play a key role in many areas: They are crucial for the storage of energy in our body as well as in batteries. In order to release energy, ions - charged atoms - must move in a liquid such as water. Until now the precise mechanism by which they move through the atoms and molecules of the electrolyte has, however, remained largely unknown. Scientists at the Max Planck Institute for Polymer Research have now shown that the electrical resistance of an electrolyte, which is determined by the motion of ions, can be traced back to microscopic vibrations of these dissolved ions.
In chemistry, common table salt is also known as sodium chloride. If this salt is dissolved in water, sodium and chloride atoms dissolve as positively or...
Drops of water falling on or sliding over surfaces may leave behind traces of electrical charge, causing the drops to charge themselves. Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz have now begun a detailed investigation into this phenomenon that accompanies us in every-day life. They developed a method to quantify the charge generation and additionally created a theoretical model to aid understanding. According to the scientists, the observed effect could be a source of generated power and an important building block for understanding frictional electricity.
Water drops sliding over non-conducting surfaces can be found everywhere in our lives: From the dripping of a coffee machine, to a rinse in the shower, to an...
90 million-year-old forest soil provides unexpected evidence for exceptionally warm climate near the South Pole in the Cretaceous
An international team of researchers led by geoscientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have now...
07.04.2020 | Event News
06.04.2020 | Event News
02.04.2020 | Event News
08.04.2020 | Interdisciplinary Research
08.04.2020 | Physics and Astronomy
08.04.2020 | Life Sciences