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      EEG Artifact Removal in TMS Studies of Cortical Speech Areas

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          Abstract

          The combination of transcranial magnetic stimulation (TMS) and electroencephalography (EEG) is commonly applied for studying the effective connectivity of neuronal circuits. The stimulation excites neurons, and the resulting TMS-evoked potentials (TEPs) are recorded with EEG. A serious obstacle in this method is the generation of large muscle artifacts from scalp muscles, especially when frontolateral and temporoparietal, such as speech, areas are stimulated. Here, TMS–EEG data were processed with the signal-space projection and source-informed reconstruction (SSP–SIR) artifact-removal methods to suppress these artifacts. SSP–SIR suppressed muscle artifacts according to the difference in frequency contents of neuronal signals and muscle activity. The effectiveness of SSP–SIR in rejecting muscle artifacts and the degree of excessive attenuation of brain EEG signals were investigated by comparing the processed versions of the recorded TMS–EEG data with simulated data. The calculated individual lead-field matrix describing how the brain signals spread on the cortex were used as simulated data. We conclude that SSP–SIR was effective in suppressing artifacts also when frontolateral and temporoparietal cortical sites were stimulated, but it may have suppressed also the brain signals near the stimulation site. Effective connectivity originating from the speech-related areas may be studied even when speech areas are stimulated at least on the contralateral hemisphere where the signals were not suppressed that much.

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          Most cited references31

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          NON-INVASIVE MAGNETIC STIMULATION OF HUMAN MOTOR CORTEX

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            Breakdown of cortical effective connectivity during sleep.

            When we fall asleep, consciousness fades yet the brain remains active. Why is this so? To investigate whether changes in cortical information transmission play a role, we used transcranial magnetic stimulation together with high-density electroencephalography and asked how the activation of one cortical area (the premotor area) is transmitted to the rest of the brain. During quiet wakefulness, an initial response (approximately 15 milliseconds) at the stimulation site was followed by a sequence of waves that moved to connected cortical areas several centimeters away. During non-rapid eye movement sleep, the initial response was stronger but was rapidly extinguished and did not propagate beyond the stimulation site. Thus, the fading of consciousness during certain stages of sleep may be related to a breakdown in cortical effective connectivity.
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              Interpreting magnetic fields of the brain: minimum norm estimates.

              The authors have applied estimation theory to the problem of determining primary current distributions from measured neuromagnetic fields. In this procedure, essentially nothing is assumed about the source currents, except that they are spatially restricted to a certain region. Simulation experiments show that the results can describe the structure of the current flow fairly well. By increasing the number of measurements, the estimate can be made more localised. The current distributions may be also used as an interpolation and an extrapolation for the measured field patterns.
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                Author and article information

                Contributors
                karita.salo@aalto.fi
                tuomas.mutanen@gmail.com
                selja.vaalto@aalto.fi
                risto.ilmoniemi@aalto.fi
                Journal
                Brain Topogr
                Brain Topogr
                Brain Topography
                Springer US (New York )
                0896-0267
                1573-6792
                9 July 2019
                9 July 2019
                2020
                : 33
                : 1
                : 1-9
                Affiliations
                [1 ]GRID grid.5373.2, ISNI 0000000108389418, Department of Neuroscience and Biomedical Engineering, , Aalto University School of Science, ; P.O. Box 12200, 00076 AALTO Espoo, Finland
                [2 ]GRID grid.15485.3d, ISNI 0000 0000 9950 5666, BioMag Laboratory, HUS Medical Imaging Center, , Helsinki University Hospital and University of Helsinki, ; P.O. Box 340, 00029 HUS Helsinki, Finland
                [3 ]GRID grid.8756.c, ISNI 0000 0001 2193 314X, Centre for Cognitive Neuroimaging, , Institute of Neuroscience and Psychology, University of Glasgow, ; Glasgow, G12 8QB UK
                [4 ]GRID grid.15485.3d, ISNI 0000 0000 9950 5666, Department of Clinical Neurophysiology, HUS Medical Imaging Center, , Helsinki University Hospital and University of Helsinki, ; P.O. Box 340, 00029 HUS Helsinki, Finland
                Author notes

                Communicated by Gregor Thut.

                Author information
                http://orcid.org/0000-0001-8872-7009
                Article
                724
                10.1007/s10548-019-00724-w
                6943412
                31290050
                35431d00-936f-4e49-8b5f-50171a338f25
                © The Author(s) 2019

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

                History
                : 24 January 2019
                : 1 July 2019
                Categories
                Original Paper
                Custom metadata
                © Springer Science+Business Media, LLC, part of Springer Nature 2020

                Neurology
                transcranial magnetic stimulation,electroencephalography,signal-space projection,source-informed reconstruction,broca’s area,wernicke’s area

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