Neurons in the brain are wired like a social network, researchers from the University of Basel say. Each nerve cell has links with many others, but the strongest bonds form between the few cells most similar to each other - like friends on Facebook.
"Like-minded neurons are strongly coupled while neurons that behave very differently from each other connect weakly or not at all," said professor Thomas Mrsic-Flogel, the leader of the research team from the University of Basel and University College London.
Nerve cells form a bewildering meshwork of connections called synapses - up to several thousand per cell. Yet not all synaptic connections are equal. The overwhelming majority of connections are weak, and cells make only a few strong links.
For the study, the team focused on the visual area of the cerebral cortex, which receives information from the eye and gives rise to visual perception. Neurons in this part of the brain respond to particular visual patterns but it is difficult to untangle which cells are synaptically connected because there are many thousands of them densely packed.
Using a combination of high resolution imaging and sensitive electrical measurements, the researchers found that connections between nearby neurons are organised like a social network.
Sites like Facebook keep us in contact with large numbers of acquaintances, but most people have a much smaller circle of close friends. These are usually the friends with which we have most in common, and their opinions can be more important to us than the views of the rest.
"Weak contacts in the brain have little impact, despite being in the majority," Mrsic-Flogel added. But why do neurons share such large numbers of weak connections? "We think this might have to do with learning.
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If neurons need to change their behaviour, weak connections are already in place to be strengthened, perhaps ensuring rapid plasticity in the brain," explained Lee Cossell, one of the lead authors of the study.
As a result, the brain could quickly adapt to changes in the environment. The research that explores how neurons connect will also be important for understanding neurological diseases, the authors concluded in a paper published in the journal Nature.