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Transcranial magnetic stimulation (TMS) evokes neuronal activity in the targeted cortex and connected brain regions. The evoked brain response can be measured with electroencephalography (EEG). TMS combined with simultaneous EEG (TMS−EEG) is widely used for studying cortical reactivity and connectivity at high spatiotemporal resolution. Methodologically, the combination of TMS with EEG is challenging, and there are many open questions in the field. Different TMS−EEG equipment and approaches for data collection and analysis are used. The lack of standardization may affect reproducibility and limit the comparability of results produced in different research laboratories. In addition, there is controversy about the extent to which auditory and somatosensory inputs contribute to transcranially evoked EEG. This review provides a guide for researchers who wish to use TMS−EEG to study the reactivity of the human cortex. A worldwide panel of experts working on TMS−EEG covered all aspects that should be considered in TMS−EEG experiments, providing methodological recommendations (when possible) for effective TMS−EEG recordings and analysis. The panel identified and discussed the challenges of the technique, particularly regarding recording procedures, artifact correction, analysis, and interpretation of the transcranial evoked potentials (TEPs). Therefore, this work offers an extensive overview of TMS−EEG methodology and thus may promote standardization of experimental and computational procedures across groups., Transcranial magnetic stimulation (TMS) evokes neuronal activity in the targeted cortex and connected brain regions. The evoked brain response can be measured with electroencephalography (EEG). TMS combined with simultaneous EEG (TMS−EEG) is widely used for studying cortical reactivity and connectivity at high spatiotemporal resolution. Methodologically, the combination of TMS with EEG is challenging, and there are many open questions in the field. Different TMS−EEG equipment and approaches for data collection and analysis are used. The lack of standardization may affect reproducibility and limit the comparability of results produced in different research laboratories. In addition, there is controversy about the extent to which auditory and somatosensory inputs contribute to transcranially evoked EEG. This review provides a guide for researchers who wish to use TMS−EEG to study the reactivity of the human cortex. A worldwide panel of experts working on TMS−EEG covered all aspects that should be considered in TMS−EEG experiments, providing methodological recommendations (when possible) for effective TMS−EEG recordings and analysis. The panel identified and discussed the challenges of the technique, particularly regarding recording procedures, artifact correction, analysis, and interpretation of the transcranial evoked potentials (TEPs). Therefore, this work offers an extensive overview of TMS−EEG methodology and thus may promote standardization of experimental and computational procedures across groups.

Transcranial magnetic stimulation (TMS) can non-invasively excite cortical neurons. The evoked neuronal activation shows in the extracranial electroencephalogram (EEG). Tracking down the activation cascade is called the EEG inverse problem. The problem has no unique solution, and even small changes in the EEG data, such as measurement noise, can elicit large changes in the solutions. TMS also gives rise to high-amplitude artifacts in EEG, which further complicates the analysis. In this work, the aim was to model a multitude of distributed sources in the cortex. Bayesian framework was adopted, which involves modeling uncertain quantities with probability distributions. Noise, source strengths and their variances were chosen as the uncertain quantities. Adjusting the variances during the estimation has the advantage of allowing some of the sources to become signicantly larger than the others and easily distinguishable. TMS-induced artifacts were also modeled during the inverse estimations. The simulation results show that a few supercial sources and one large artifact are quite well estimated. Two measured data sets were also analyzed., Transkraniaalisen magneettistimulaation (TMS) avulla voidaan aktivoida aivokuoren neuroneita ja elektroenkefalografialla (EEC) voidaan mitata syntyvää neuronaalista toimintaa, molempia kallon ulkopuolelta. Aktivaatiokaskadin jäljittämistä kutsutaan EEG-käänteisongelmaksi. Tällä ongelmalla ei ole yksikäsitteistä ratkaisua, ja pienetkin häiriöt signaalissa voivat aiheuttaa suuria vääristymiä ratkaisuihin. TMS aiheuttaa EEG-signaaliin myös suuria artefaktoja, mikä hankaloittaa ongelmaa. Tässä työssä pyrittiin mallintamaan useita korteksille sijoitettuja lähteitä. Estimointiin käytettiin bayesilaista lähestymistapaa, jossa mallin epävarmoja suureita kuvataan todennäköisyysjakaumin. Tässä työssä nämä suureet olivat kohina, lähdevoimakkuudet ja lähdevarianssit. Kun varianssit sovitetaan datasta, saavat jotkin lähdevoimakkuudet kasvaa huomattavasti muita suuremmiksi, ja tärkeät lähteet on helpompi havaita. Lähteiden lisäksi työssä estimoitiin TMS:n synnyttämiä artefaktoja. Tuloksista käy ilmi, että pinnallisesti sijaitsevat lähteet sekä suuri yksittäinen artefakta ovat melko hyvin estimoitavissa simuloidulle datalle. Myös kaksi mittausta analysoitiin.