title: Revealing time-unlocked brain activity from MEG measurements by common waveform estimation.
abstract: Brain activities related to cognitive functions, such as attention, occur with unknown and variable delays after stimulus onsets. Recently, we proposed a method (Common Waveform Estimation, CWE) that could extract such brain activities from magnetoencephalography (MEG) or electroencephalography (EEG) measurements. CWE estimates spatiotemporal MEG/EEG patterns occurring with unknown and variable delays, referred to here as unlocked waveforms, without hypotheses about their shapes. The purpose of this study is to demonstrate the usefulness of CWE for cognitive neuroscience. For this purpose, we show procedures to estimate unlocked waveforms using CWE and to examine their role. We applied CWE to the MEG epochs during Go trials of a visual Go/NoGo task. This revealed unlocked waveforms with interesting properties, specifically large alpha oscillations around the temporal areas. To examine the role of the unlocked waveform, we attempted to estimate the strength of the brain activity of the unlocked waveform in various conditions. We made a spatial filter to extract the component reflecting the brain activity of the unlocked waveform, applied this spatial filter to MEG data under different conditions (a passive viewing, a simple reaction time, and Go/NoGo tasks), and calculated the powers of the extracted components. Comparing the powers across these conditions suggests that the unlocked waveforms may reflect the inhibition of the task-irrelevant activities in the temporal regions while the subject attends to the visual stimulus. Our results demonstrate that CWE is a potential tool for revealing new findings of cognitive brain functions without any hypothesis in advance.
authors.affiliation: Department of Computational Brain Imaging, ATR Neural Information Analysis Laboratories, Kyoto, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Takeda
authors.affiliation: Graduate School of Human Life Sciences, Showa Women's University, Tokyo, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yamanaka
authors.affiliation: Department of Cognitive Neuroscience, ATR Cognitive Mechanisms Laboratories, Kyoto, Japan; Brain Networks and Communication Laboratory, Center for Information and Neural Networks, National Institute of Information and Communications Technology, Osaka, Japan; Japan Science and Technology Agency, PRESTO, Saitama, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Yamagishi
authors.affiliation: Department of Computational Brain Imaging, ATR Neural Information Analysis Laboratories, Kyoto, Japan.
authors.forename: Masa-aki
authors.initials: MA
authors.lastname: Sato
mesh_terms: D000328:Adult; D001288:Attention / Q000502:physiology; D001307:Auditory Perception / Q000502:physiology; D001921:Brain / Q000502:physiology*; D058256:Brain Waves; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D011930:Reaction Time / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors