PT  - JOURNAL ARTICLE
AU  - Mana Biabani
AU  - Alex Fornito
AU  - Tuomas P. Mutanen
AU  - James Morrow
AU  - Nigel C. Rogasch
TI  - Characterizing and minimizing the contribution of sensory inputs to TMS-evoked potentials
AID  - 10.1101/489864
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 489864
4099  - http://biorxiv.org/content/early/2018/12/09/489864.short
4100  - http://biorxiv.org/content/early/2018/12/09/489864.full
AB  - Background Transcranial magnetic stimulation (TMS) evokes voltage deflections in electroencephalographic (EEG) recordings, known as TMS-evoked potentials (TEPs), which are increasingly used to study brain dynamics. However, the extent to which TEPs reflect activity directly evoked by magnetic rather than sensory stimulation is unclear.Objective To characterize and minimize the contribution of sensory inputs to TEPs.Methods Twenty-four healthy participants received TMS over the motor cortex using two different intensities (subthreshold, supra-threshold) and waveforms (monophasic, biphasic). TMS was also applied over the shoulder as a multisensory control condition. Common sensory attenuation measures, including coil padding and noise masking, were adopted. We examined spatiotemporal relationships between the EEG responses to the scalp and shoulder stimulations at sensor and source levels. Furthermore, we compared three different filters (independent component analysis, signal-space projection with source-informed reconstruction (SSP-SIR) and linear regression) designed to attenuate the impact of sensory inputs on TEPs.Results The responses to the scalp and shoulder stimulations were correlated in both temporal and spatial domains, especially after ~60 ms, regardless of the intensity and stimuli waveform. However, the outputs of all filtering methods confirmed that TEPs cannot be entirely explained by sensory potentials. Among the three filters, SSP-SIR showed a good trade-off between preserving early TEPs, while correcting sensory-contaminated late components.Conclusions The findings demonstrate that motor TEPs reflect a combination of TMS-evoked and sensory-evoked neural activity, highlighting the importance of adopting sensory control conditions in TMS-EEG studies. Offline filters show promise for isolating TMS-evoked neural activity from sensory-evoked potentials.HighlightsEEG responses to TMS over M1 (TEPs) and shoulder (SEPs) were comparedLong latency components (> ~60ms) were correlated between TEPs and SEPsChanging TMS intensities and waveforms did not alter TEP-SEP relationshipsHowever, TEPs cannot be entirely explained by SEPsOffline filters showed promise for isolating TMS-evoked neural activity