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Hand, die mit gelbem Highlighter eine Publikation markiert. Daneben ein Charité-Kaffeebecher.

From the source: New findings on brain networks


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Charité researchers discover "complexome"

Researchers from Charité – Universitätsmedizin Berlin and the Max Planck UCL Centre for Computational Psychiatry and Ageing Research report new findings on the organizational principles of spontaneous brain activity. In this section, they answer questions about their research findings.

What was the research question or scientific inquiry behind your study?

Zwei Schemata einer Hirnhälfte mit gelben und unterschiedlich stark blau eingefärbten Bereichen.
Distribution of signal complexity, displayed here for the left hemisphere (upper row: lateral view, lower row: medial view). On average, the activity of yellow areas shows higher complexity. In contrast, regions colored in blue show lower signal complexity – here, the spontaneous episodes of low complexity (“complexity drops”) occur particularly often. © Charité | Stephan Krohn

The past 20 years of neuroscience have shown that the human brain operates in large-scale functional networks. Although the spatiotemporal organization of these networks has become increasingly clear, it is an open question what precisely gives rise to these organizational principles. Here we explored this question by linking the activity patterns of individual brain regions to the network architecture of the brain as a whole.

How did you approach the topic?

We studied the spontaneous brain activity of healthy adults in the resting state, whose brain signals were recorded with functional magnetic resonance imaging (MRI) as part of the Human Connectome Project. These brain signals were then subjected to a complexity analysis that rests on the information-theoretic concept of entropy. With this approach, we were able to detect patterns of brain activity that are not captured by alternative methods.

What did you discover?

The key observation is that the brain operates in distinct states of complexity that explain several important network properties. Specifically, we show that brain activity is highly irregular most of the time, which is reflected by a high degree of complexity. However, this “default state” is recurrently interrupted by spontaneous episodes of low complexity (“complexity drops”), in which brain activity becomes much more regular for a short moment in time.

Was there anything that surprised you?

It was surprising to find that this complexity pattern was present in every one of nearly 700 MRIs, which hints at a rather fundamental organizational principle that we summarize as a human “complexome”. We were also surprised by the pronounced effects of age on these activity patterns, even though the study cohort comprised young adults in their 20s and 30s.

What’s your takeaway?

Our findings reconcile several important insights into the functional organization of the human brain, offering an explanation for why brain areas act in functional networks and how activity patterns spread across the brain over time. Furthermore, our approach explains how brain networks change on the scale of seconds to minutes and creates a link between functional and anatomical network properties. Our work also shows a link between complexity and age as well as cognitive and motor performance in healthy individuals.


Krohn S et al. A spatiotemporal complexity architecture of human brain activity. Sci Adv 2023 Feb 01. doi: 10.1126/sciadv.abq3851