The human brain has evolved over eons of time to develop the most complex and unique network to support the strong brain functions. So far, it is well known that the brain network has characteristic features such as small world, scale-free, community, and rich-club etc. However, we know little about how these features ensure strong brain functions or what are the mechanisms of brain functions. Recently, a team from East China Normal University and Hong Kong Baptist University (S. Huo, C. Tian, M. Zheng, S. Guan, C.S. Zhou, and Z. Liu) published a paper in National Science Review, which revealed that the real brain network has a new chimera state----spatial multi-scaled chimera state, and its formation is closely related the local symmetry of connections (see figure 1).
Different from artificial complex networks, the team considered a real network of cerebral cortex and let each node be represented by a neural mass model describing the mean field activity of a neuronal population. They paid attention to the collective behaviors of two brain networks with different sizes (one has 989 nodes and the other has 64 nodes) and found that the brain network may have a surprising behavior, i.e. global trivial but with local chimera state, depending on coupling strengths and time-delays. Further, the authors revealed that it is possible to have chimera states on both global and local levels, and thus call it spatial multi-scaled chimera state (see figure 2).
To understand the mechanism of spatial multi-scaled chimera state, the team further studied the topological symmetry of each cortical region and found that there is a positive correlation between the degree of symmetry and synchronization, i.e. the regions with higher symmetry take the role of relay nodes. Moreover, the team also studied both the structural and functional bifurcation trees of clusters and discovered the close relationship between network structure and functions. That is, for different network status, no matter it is normal or abnormal, the activation of different clusters or their combinations can result in different dynamical brain modes and thus implement the different rhythms such as the δ, θ, α, β and γ waves.
The discovery of spatial multi-scaled chimera state may be used to explain the experiments of brain rhythms and the diversity of chimera states may be used to explain the cognitive patterns of brain network. Thus, the new idea to study the formation of dynamical patterns from symmetry may provide a new approach to understand the mechanism of brain functions.
See the article:
Spatial multi-scaled chimera states of cerebral cortex network and its inherent structure-dynamics relationship in human brain