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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.

Modulatory effects of transcranial magnetic stimulation (TMS) strongly depend on the stimulation parameters. Here, we compared the immediate, task-locked inhibitory effects on speech-related muscles and the tolerability of different TMS protocols during a language production task. Repetitive TMS (rTMS) and paired-pulse TMS (PP) were applied in 13 healthy subjects over the primary motor cortex (M1) during a finger-tapping/tongue-twisting tasks. The lowest subject-specific TMS intensity leading to movement disruptions wasused for TMS over left-sided speech-related areas during picture naming. Here, time-locked PP and rTMS (10/30/50Hz; randomized sequence) were applied. Cortical silent periods (cSPs) were analyzed from electromyography obtained from various face muscles. 30Hz- and 50Hz-rTMS reliably evoked tongue movement disruption (ICC=0.65) at lower rTMS intensities compared to 10Hz-rTMS or PP. CSPs were elicited from the left hemisphere by all TMS protocols, most reliably by PP (p<0.001). Also, cSPs with longest durations were induced by PP. Exploratory analyses of PP suggest that the trials with strongest motor inhibitory effects (presence of cSP) were associated with more articulatory naming errors, hence hinting at the utility of TMS-elicited, facial cSP for mapping of language production areas. Higher-frequency rTMS and PP evoked stronger inhibitory effects as compared to 10Hz-rTMS during a language task, thus enabling a probably more efficient and tolerable routine for language mapping. The spatial distribution of cranial muscle cSPs implies that TMS might affect not only M1, but also distant parts of the language network.

Yhdistämällä transkraniaalinen magneettistimulaatio (TMS) ja aivosähkökäyrä (EEG) voidaan aivokuoren reaktiivisuutta ja konnektivisuutta tutkia ei-invasiivisesti. Menetelmä on vielä melko vähän sovellettu, sillä TMS aiheuttaa EEG:hen suuria artefaktoja, joita on vaikea poistaa nykyisillä signaalinkäsittelymenetelmillä. Tässä diplomityössä EEG:n mittaus ja primäärisen näköaivokuoren TMS-stimulointi (TMS-EEG) suoritettiin samanaikaisesti. Tavoitteena oli käyttää riippumattomien komponenttien analyysiä (ICA) artefaktojen poistoon ja tarkastella stimulaation aiheuttamia EEG-vasteita ja keinotekoisia näköhavaintoja eli fosfiineja. Diplomityö käsitti TMS-EEG- ja TMS-mittaukset, joissa molemmissa käytettiin viittä eri paripulssi-, yhtä yksittäispulssi- sekä yhtä kontrolliprotokollaa. Työssä ICA:ta sovellettiin primääriseltä näköaivokuorelta mitattuun EEG:hen ja tutkittiin paripulssiprotokollien aiheuttamia primäärisen näköaivokuoren vasteita ihmisillä ensimmäistä kertaa. Työssä havaittiin, että ICA soveltui artefaktojen poistoon primäärisen näköaivokuoren EEG:stä. Lisäksi paripulssiprotokollien aiheuttamista vasteista ei löydetty eroavaisuuksia verrattaessa niitä yksittäispulssiprotokollan vasteisiin. Vain vasteiden spatiaalinen leviäminen erosi merkittävästi. Data-analyysi paljasti kuitenkin mittausasetelmassa lukuisia ongelmia, jotka tulisi korjata ennen kuin luotettavia johtopäätöksiä voidaan tehdä., By combining transcranial magnetic stimulation (TMS) and electroencephalography (EEG) cortical excitability and connectivity can be studied non-invasively. However, the method is still at an early stage as TMS causes large muscle artefacts to the EEG that are difficult to remove with the existing signal processing methods. In this master's thesis the combination of simultaneous TMS and EEG (TMSEEG) was applied to the primary visual cortex. The aim was to use independent component analysis (ICA) to clean the data from artefacts and to explore the neural EEG responses and artificial visual percepts, phosphenes, evoked by the stimulation. The thesis covered a TMS-EEG and a TMS study, which both had five different paired-pulse protocols, a single pulse protocol, and a control protocol. This was the first time ICA was applied to the primary visual cortex EEG, as well as the first time the human primary visual cortex neural responses to paired-pulse TMS were studied. It was found that ICA removed the TMS-evoked artefacts from the primary visual cortex EEG. In addition, the responses to the paired-pulse stimulation showed no significant differences when compared with the single pulse protocol. Only the spatial spreading of the responses differed significantly. However, the data analysis revealed several problems in the experimental design that need to be fixed before reliable conclusions can be drawn.