Functional Modularity of Background Activities in Normal and Epileptic Brain Networks

We analyze the connectivity structure of weighted brain networks extracted from spontaneous magnetoencephalographic signals of healthy subjects and epileptic patients (suffering from absence seizures) recorded at rest. We find that, for the activities in the 5–14 Hz range, healthy brains exhibit a sparse connectivity, whereas the brain networks of patients display a rich connectivity with a clear modular structure. Our results suggest that modularity plays a key role in the functional organization of brain areas during normal and pathological neural activities at rest.

Figure 1

Topographic distribution of node strength $s_i$ (a), weighted clustering coefficient $c_i$ (b), and efficiency $E_i$ (c). Control subjects (CTL), patients (PAT), and difference maps ($p$ values) of their comparison are reported for real and equivalent random configurations.

Figure 2

(a) Brain sites belonging to each functional brain module were colored and superimposed onto an anatomical image (there is no color correspondence between the modules of patients and those of controls). For the sake of clarity, isolated nodes were colored in black. Topographic distribution and difference maps ($p$ values) of participation coefficient (b) and within-module degree (c) for real and equivalent random graphs.