30In this paper we have reconstructed electroencephalography (EEG) sources using weighted 31 Minimum Norm Estimator (wMNE) for visual oddball experiment to estimate brain functional 32 networks. Secondly we have evaluated the impact of time-frequency decomposition algorithms 33 and scout functions on brain functional networks estimation using phase-locked value (PLV). 34 Lastly, we compared the difference between target stimuli with response (TR) and non-target 35 with no response (NTNR) cases in terms of brain functional connectivity (FC). We acquired 36 the EEG data from 20 healthy participants using 129 channels EEG sensor array for visual 37 oddball experiment. Three scout functions: i) MEAN, ii) MAX and iii) PCA were used to 38 extract the regional time series signals. We transformed the regional time series signals into 39 complex form using two methods: i) Wavelet Transform (WT) and ii) Hilbert Transform (HT).
40The instantaneous phases were extracted from the complex form of the regional time series 41 signals. The FC was estimated using PLV. The joint capacity of the time-frequency 42 decomposition algorithms/scout functions applied to reconstructed EEG sources was evaluated 43 using two criteria: i) localization index (LI) and ii) R. The difference in FC between TR and 44 NTNR cases was evaluated using these two criteria. Our results show that the WT has higher 45 impact on LI values and it is better than HT in terms of consistency of the results as the standard 46 deviation (SD) of WT is lower. In addition, WT/PCA pair is better than other pairs in terms of 47 consistency as the SD of the pair is lower. This pair is able to estimate the connectivity within 48 parietal region which corresponds to P300 response; although WT/MEAN is also able to do 49 that, However, WT/PCA has lower SD than WT/MEAN. Lastly, the differences in connectivity 50 between TR and NTNR cases over parietal, central, right temporal and limbic regions which 51 correspond to target detection, P300 response and motor response were observed. Therefore, 52 we conclude that the output of the connectivity estimation might be affected by time-frequency 53 decomposition algorithms/scout functions pairs. Among the pairs, WT/PCA yields best results 54 for the visual oddball task. Moreover, TR and NTNR cases are different in terms of estimated 55 functional networks. 56 57 and non-linear methods are widely used for FC estimations in the sensor space [50-52] as well 102 as source space [53-56]. 103 Based on the literature review it is observed that the estimated FC depends on the 104 algorithms to solve the EEG ill-posed inverse problem and the methods for connectivity 105 estimation. Hassan et al. reported that the use of wMNE in conjunction with the phase-locking 106 value (PLV) provides better results as compared to the other combinations in the sensor space 107 [26,57]. This combination has been adapted for FC analysis in the source space [25,58-60]. 108 In this research, we planned to utilized wMNE to reconstruct the dipolar so...