New model brings astrocytes into large-scale brain simulations

Astrocytes are a subtype of glial cells and estimated to be the most numerous types of glial cells in the brain. These star-shaped cells perform several complex functions in the brain and interact with neurons, synapses, other glial cell types and blood vessels. However, they are often overlooked. 

In this study, published on PLOS Computational Biology and carried out in collaboration between teams at Tampere University (Finland), Forschungszentrum Jülich (Germany) and the Norwegian University of Life Sciences (Norway), the researchers proposed a new, flexible, and scalable connectivity concept to represent how neurons and astrocytes interact in networks. 

While traditional brain network models focus on neuron-to-neuron interactions (or “bipartite synapses”), astrocytes often form so called “tripartite synapses” that connect two neurons and an astrocyte. The team formalised this pattern as a new connection rule, offering a more realistic way to capture how astrocytes influence neural communication. 

“We developed a method that creates such tripartite connectivity flexibly and efficiently, even when simulations are spread across a large supercomputer,” explained Hans Ekkehard Plesser, one of the senior contributors. 

The new technology extends the NEST for spiking neural network models simulator and made it possible to simulate up to one million interconnected cells, while earlier studies comprised at best a few thousand cells. Such large-scale simulations promise to offer new insights into how local neuron–astrocyte interactions can shape global brain dynamics. 

The authors have also published online tutorials to help users get started with the new technology, which is openly available on EBRAINS. 

A collaborative effort 

The work originated during the Human Brain Project, continued as an HBP Voucher Project implementing the new connectivity concept in NEST, and later progressed under EBRAINS 2.0, exemplifying how EBRAINS fosters collaborative development of advanced computational tools for neuroscience. 

“This experience perfectly illustrates the importance of the HBP as a network”, says Marja-Leena Linne, head of Computational Neuroscience Group at Tampere University and study lead.  

“It provided a truly open and collaborative environment where researchers could exchange ideas freely without fear of losing ownership of their work. This collaborative spirit was very valuable and played a decisive role in the success of this study”, she adds. 

“Additionally, the formalised description of neuron-astrocyte connectivity that we have devised facilitates the precise specification of complex network models involving astrocytes and thus the reproducibility of scientific results” adds co-author Markus Diesmann, director at the Institute for Advance Simulation in Jülich. 

It also integrates experimental data to a greater extent than existing studies. “A key strength of this work is the extensive use of experimental data to fine-tune the astrocyte model implementation in NEST,” says Marja-Leena Linne. “The model builds on experimental findings that I have collected and analysed over three decades, complemented by results from the broader literature, making it one of the most biologically grounded implementations of neuron–astrocyte interactions.” 

By making astrocytes part of large-scale brain simulations, the study opens the door to more realistic models of how brain circuits organise and function.