Hemifield-dependent N1 and event-related theta/delta oscillations: An unbiased comparison of surface Laplacian and common EEG reference choices

Abstract

Surface Laplacian methodology has been used to reduce the impact of volume conduction and arbitrary choice of EEG recording reference for the analysis of surface potentials. However, the empirical implications of employing these different transformations to the same EEG data remain obscure. This study directly compared the statistical effects of four commonly-used (nose, linked mastoids, average) or recommended (reference electrode standardization technique [REST]) references and their spherical spline current source density (CSD) transformation for a large data set stemming from a well-understood experimental manipulation. ERPs (72 sites) recorded from 130 individuals during a visual half-field paradigm with highly-controlled emotional stimuli were characterized by mid-parietooccipital N1 (125 ms peak latency) and event-related synchronization (ERS) of theta/delta (160 ms), which were most robust over the contralateral hemisphere. All five data transformations were rescaled to the same covariance and submitted to a single temporal or time-frequency PCA (Varimax) to yield simplified estimates of N1 or theta/delta ERS. Unbiased nonparametric permutation tests revealed that these hemifield-dependent asymmetries were by far most focal and prominent for CSD data, despite all transformations showing maximum effects at mid-parietooccipital sites. Employing smaller subsamples (signal-to-noise) or window-based ERP/ERS amplitudes did not affect these comparisons. Furthermore, correlations between N1 and theta/delta ERS at these sites were strongest for CSD and weakest for nose-referenced data. Contrary to the common notion that the spatial high pass filter properties of a surface Laplacian reduce important contributions of neuronal generators to the EEG signal, the present findings demonstrate that instead volume conduction inherent in surface potentials weakens the representation of neuronal activation patterns at scalp that directly reflect regional brain activity.

Enhancement of brain event-related potentials to speech sounds is associated with compensated reading skills in dyslexic children with familial risk for dyslexia

“…However, a recent study comparing the reference schemes show that the reference used has not remarkable impact on results if brain area used in analyses corresponds the areas were the actual sources are (Kayser & Tenke, 2015b). In the case of the current research, it is assumed that primary sources of the activation to the auditory stimuli are bilaterally at the auditory cortices.…”

“…In theory, the sum of all recorded EEG activity approximates zero, and because no neutral reference location exists on the human body because of volume conduction, the average reference has been preferred to all other known reference schemes when using high denseelectrode arrays (e.g., Dien, 1998;Kayser & Tenke, 2015b;Nunez & Srinivasan, 2006). The data analyzed in Study III was collected with DSAMP data acquisition software in 1990's with a limited number of channels available in the system, which made the average-referencing infeasible solution.…”

Issues and considerations for using the scalp surface Laplacian in EEG/ERP research: A tutorial review

“…Using EEGs recorded from a large sample ( N = 130) during a visual half-field paradigm, we found that CSDs revealed by far a more accurate representation of hemifield-dependent asymmetries of the posterior contralateral N1, both in time and time-frequency domains, than their surface potentials counterparts, regardless of reference scheme (average, nose, linked mastoids, reference electrode standardization technique [REST]; Kayser and Tenke, 2015). In contrast, surface potentials also revealed significant hemifield-dependent asymmetries at more anterior locations, which were presumably caused by volume conduction.…”

“…After reducing the signal-to-noise ratio by limiting the number of trials to compute an error-related negativity, the surface Laplacian was found to render better results than its surface potential counterparts (Cohen, 2014). We manipulated noise levels by evaluating hemifield-dependent N1 asymmetries with nonparametric permutation tests using different sample sizes ( N = 130, 80, 40, 20, or 10), which did not affect the superior performance of CSD compared to ERP or EEG measures, although overall statistical significance progressively declined with smaller sample size across all data transformations (Kayser and Tenke, 2015). …”

Surface Laplacians (SL) and phase properties of EEG rhythms: Simulated generators in a volume-conduction model

“…In our previous work, obtained for a groups of subjects rather than a single individual, CSD topographies computed with intermediate spline flexibility (m = 4) were stable and interpretable, both for ERP and resting EEG (e.g., Kayser and Tenke, 2006a, b; Tenke and Kayser, 2005; Tenke et al, 2010, 2011), as well as for event-related sychronization/desychronization (Kayser et al, 2014; Kayser and Tenke, 2015a). The present findings extend these recommendations to the study of phase properties of neuronal oscillatory activity.…”