Abstract
ObjectivesFunctional connectivity (FC) is increasingly used as target for neuromodulation and enhancement of performance. A reliable assessment of FC with electroencephalography (EEG) currently requires a laboratory environment with high-density montages and a long preparation time. This study investigated the feasibility of reconstructing source FC with a low-density EEG montage towards a usage in real life applications.MethodsSource FC was reconstructed with inverse solutions and quantified as node degree of absolute imaginary coherence in alpha frequencies. We used simulated coherent point sources as well as two real datasets to investigate the impact of electrode density (19 vs. 128 electrodes) and usage of template vs. individual MRI-based head models on localization accuracy. In addition, we checked whether low-density EEG is able to capture inter-individual variations in coherence strength.ResultsIn numerical simulations as well as real data, a reduction of the number of electrodes led to less reliable reconstructions of coherent sources and of coupling strength. Yet, when comparing different approaches to reconstructing FC from 19 electrodes, source FC obtained with beamformers outperformed sensor FC, FC computed after independent component analysis, and source FC obtained with sLORETA. In particular, only source FC based on beamformers was able to capture neural correlates of motor behavior.ConclusionReconstructions of FC from low-density EEG is challenging, but may be feasible when using source reconstructions with beamformers.
Highlights
Interregional neural communication is thought to be accompanied by a synchronization of oscillations between different brain regions (Aertsen et al 1989; Varela et al 2001)
We observed that the localization accuracy was significantly better when using minimum variance beamformer (MVBF) than standardized low-resolution electromagnetic tomography (sLORETA) at all signal-to-noise ratio (SNR) (F1,911 = 351, p < 0.0001), in accordance with previous findings from high-density settings (Guggisberg et al 2011)
Localization error was significantly influenced by the montage and head model (F2,911 = 85, p < 0.0001) with a rapid drop in localization accuracy when using a template head model and low density montages in MVBF
Summary
Interregional neural communication is thought to be accompanied by a synchronization of oscillations between different brain regions (Aertsen et al 1989; Varela et al 2001). FC is increasingly used as marker to probe for novel disease biomarkers (Fox and Greicius 2010) or predictors of outcome (Westlake et al 2012; Nicolo et al 2015). It has become a target for new treatment approaches aiming at enhancing performance or reducing neurological deficits. The setup of a neurofeedback as performed in a laboratory is time-consuming and tiring for the patients It requires individual head models based on magnetic resonance imaging (MRI), and high-density electroencephalography (hd-EEG). Such installation is hardly feasible in routine clinical practice or at a larger scale
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