title: Identifying Granger causal relationships between neural power dynamics and variables of interest.
abstract: Power modulations of oscillations in electro- and magnetoencephalographic (EEG/MEG) signals have been linked to a wide range of brain functions. To date, most of the evidence is obtained by correlating bandpower fluctuations to specific target variables such as reaction times or task ratings, while the causal links between oscillatory activity and behavior remain less clear. Here, we propose to identify causal relationships by the statistical concept of Granger causality, and we investigate which methods are bests suited to reveal Granger causal links between the power of brain oscillations and experimental variables. As an alternative to testing such causal links on the sensor level, we propose to linearly combine the information contained in each sensor in order to create virtual channels, corresponding to estimates of underlying brain oscillations, the Granger-causal relations of which may be assessed. Such linear combinations of sensor can be given by source separation methods such as, for example, Independent Component Analysis (ICA) or by the recently developed Source Power Correlation (SPoC) method. Here we compare Granger causal analysis on power dynamics obtained from i) sensor directly, ii) spatial filtering methods that do not optimize for Granger causality (ICA and SPoC), and iii) a method that directly optimizes spatial filters to extract sources the power dynamics of which maximally Granger causes a given target variable. We refer to this method as Granger Causal Power Analysis (GrangerCPA). Using both simulated and real EEG recordings, we find that computing Granger causality on channel-wise spectral power suffers from a poor signal-to-noise ratio due to volume conduction, while all three multivariate approaches alleviate this issue. In real EEG recordings from subjects performing self-paced foot movements, all three multivariate methods identify neural oscillations with motor-related patterns at a similar performance level. In an auditory perception task, the application of GrangerCPA reveals significant Granger-causal links between alpha oscillations and reaction times in more subjects compared to conventional methods.
authors.affiliation: Machine Learning Laboratory, Berlin Institute of Technology, Marchstr. 23, 10587 Berlin, Germany. Electronic address: irene.winkler@tu-berlin.de.
authors.forename: Irene
authors.initials: I
authors.lastname: Winkler
authors.affiliation: Machine Learning Laboratory, Berlin Institute of Technology, Marchstr. 23, 10587 Berlin, Germany; Neural Engineering Group, Department of Biomedical Engineering, The City College of New York, New York City, NY, USA; Bernstein Focus Neurotechnology, Berlin, Germany. Electronic address: shaufe@ccny.cuny.edu.
authors.forename: Stefan
authors.initials: S
authors.lastname: Haufe
authors.affiliation: Machine Learning Laboratory, Berlin Institute of Technology, Marchstr. 23, 10587 Berlin, Germany; Bernstein Focus Neurotechnology, Berlin, Germany; Bernstein Center for Computational Neuroscience, Berlin, Germany.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Porbadnigk
authors.affiliation: Machine Learning Laboratory, Berlin Institute of Technology, Marchstr. 23, 10587 Berlin, Germany; Bernstein Focus Neurotechnology, Berlin, Germany; Bernstein Center for Computational Neuroscience, Berlin, Germany; Department of Brain and Cognitive Engineering, Korea University, Anam-dong, Seongbuk-gu, Seoul 136-713, Republic of Korea. Electronic address: klaus-robert.mueller@tu-berlin.de.
authors.forename: Klaus-Robert
authors.initials: KR
authors.lastname: Müller
authors.affiliation: Machine Learning Laboratory, Berlin Institute of Technology, Marchstr. 23, 10587 Berlin, Germany; Bernstein Center for Computational Neuroscience, Berlin, Germany. Electronic address: sven.daehne@tu-berlin.de.
authors.forename: Sven
authors.initials: S
authors.lastname: Dähne
mesh_terms: D000328:Adult; D000513:Alpha Rhythm / Q000502:physiology; D001307:Auditory Perception / Q000502:physiology; D002540:Cerebral Cortex / Q000502:physiology*; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D004569:Electroencephalography / Q000379:methods*; D055724:Electrophysiological Phenomena / Q000502:physiology*; D006801:Humans; D015225:Magnetoencephalography / Q000379:methods*; D008959:Models, Neurological; D009043:Motor Activity / Q000502:physiology
keywords: EEG; Granger causality; MEG; Oscillations