Identifying electrode bridging from electrical distance distributions: A survey of publicly-available EEG data using a new method

·An algorithm was developed to identify bridged electrodes using characteristics of electrical distance frequency distributions.·Using this tool on five publically-available datasets, electrode bridges were detected in 54% of sessions.·If used routinely, this automated approach offers feedback required to protect against spatial distortion and smoothing that might contaminate an EEG or ERP topography.

ObjectiveEEG topographies may be distorted by electrode bridges, typically caused by electrolyte spreading between adjacent electrodes. We therefore sought to determine the prevalence of electrode bridging and its potential impact on the EEG literature.MethodsFive publicly-available EEG datasets were evaluated for evidence of bridging using a new screening method that employs the temporal variance of pairwise difference waveforms (electrical distance). Distinctive characteristics of electrical distance frequency distributions were used to develop an algorithm to identify electrode bridges in datasets with different montages (22–64 channels) and noise properties.ResultsThe extent of bridging varied substantially across datasets: 54% of EEG recording sessions contained an electrode bridge, and the mean percentage of bridged electrodes in a montage was as high as 18% in one of the datasets. Furthermore, over 40% of the recording channels were bridged in 9 of 203 sessions. These findings were independently validated by visual inspection.ConclusionsThe new algorithm conveniently, efficiently, and reliably identified electrode bridges across different datasets and recording conditions. Electrode bridging may constitute a substantial problem for some datasets.SignificanceGiven the extent of the electrode bridging across datasets, this problem may be more widespread than commonly thought. However, when used as an automatic screening routine, the new algorithm will prevent pitfalls stemming from unrecognized electrode bridges.