Structural-Effective Connectivity Atlas of Human Brain

Romanian Government UEFISCDI
research grant PN-III-P4-ID-PCE-2016-0588

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    SUMMARY

The scientific interest in the astounding brain complexity has significantly increase during the recent years. The technological advancements allowed for new imaging methods to emerge, methods that combined with advanced statistical tools gave birth to new ways of studying brain connectivity. However, none of these methods allow the study of effective brain connectivity, which refers to the causal relationships between various brain structures, in a deterministic fashion. Current effective connectivity methods, based on Granger causality [Granger, 19691], can only infer causality in a probabilistic way [Friston, 20112]. Knowing the effective brain connectivity is crucial in understanding the propagation of pathological activity in patients suffering from focal epilepsy.

In brain research, the term "connectivity" can refer to structural, functional or effective connectivity [Guye et al., 20083; Keller et al., 20144]. The state-of-the-art of structural connectivity studies is based on Diffusion Tensor Imaging (DTI) and Diffusion Spectrum Imaging (DSI) that are able to identify complex white matter tracts within the brain [Wedeen et al., 20055; Wedeen et al., 20086]. The functional connectivity studies the patterns of non-causal statistical dependencies between cortical areas. These patterns are often revealed by fMRI or using EEG. The effective connectivity reflects the causal interactions between different brain regions, referring to the influence one brain region exerts over another [Friston, 19947; Friston, 20118]. One of the most unambiguous way to study the effective connectivity may be represented by the analysis of responses to intracranial electrical stimulation. The electrical stimulation is the analogue of the DSI seeding process: electrical pulses are applied and their propagation is observed by recording EEG changes in remote regions of the brain. However, due to the invasive nature of the direct electrical stimulation, the possibility of using it to study the effective connectivity is restricted to the patients with drug-resistant epilepsy, undergoing the invasive pre-surgical evaluation for the localization of the seizure onset zone using subdural or depth electrodes.




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