title: 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.
authors.affiliation: Division of Cognitive Neuroscience, New York State Psychiatric Institute, New York, NY, USA; Department of Psychiatry, Columbia University College of Physicians & Surgeons, New York, NY, USA. Electronic address: kayserj@nyspi.columbia.edu.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Kayser
authors.affiliation: Division of Cognitive Neuroscience, New York State Psychiatric Institute, New York, NY, USA; Department of Psychiatry, Columbia University College of Physicians & Surgeons, New York, NY, USA.
authors.forename: Craig E
authors.initials: CE
authors.lastname: Tenke
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D002755:Choice Behavior / Q000502:physiology*; D003863:Depression / Q000503:physiopathology; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D010775:Photic Stimulation; D025341:Principal Component Analysis; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors; D014794:Visual Fields; D058067:Wavelet Analysis; D055815:Young Adult
keywords: Current source density (CSD); EEG recording reference; ERS/ERD; Event-related potentials (ERPs); Event-related spectral perturbations (ERSPs); N1pc; Permutation tests; Principal components analysis (PCA); Reference electrode standardization technique (REST); Sample size; Signal-to-noise; Surface Laplacian; Time-frequency analysis; Visual half-field (VHF) paradigm; Volume conduction