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  Effects of TMS on visual evoked potentials in a visual suppression task

Thielscher, A., Reichenbach, A., & Whittingstall, K. (2009). Effects of TMS on visual evoked potentials in a visual suppression task. Poster presented at 15th Annual Meeting of the Organization for Human Brain Mapping (HBM 2009), San Francisco, CA, USA.

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Item Permalink: http://hdl.handle.net/11858/00-001M-0000-0013-C40D-D Version Permalink: http://hdl.handle.net/21.11116/0000-0003-13F4-4
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Thielscher, A1, 2, Author              
Reichenbach, A1, 2, 3, Author              
Whittingstall, K2, 4, Author              
Affiliations:
1Former Department MRZ, Max Planck Institute for Biological Cybernetics, Max Planck Society, Spemannstrasse 38, 72076 Tübingen, DE, ou_2528700              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, Spemannstrasse 38, 72076 Tübingen, DE, ou_1497794              
3Department Human Perception, Cognition and Action, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497797              
4Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497798              

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 Abstract: Introduction It has been demonstrated that an occipital TMS pulse applied around the time of the P100 visual-evoked potential (VEP) component modifies the P100 and N150 components (Thut et al., 2003). We attempted to determine if these electrophysiological changes are linked to the behavioral visual suppression effect that occurs when occipital TMS is applied 80-100ms after onset of a briefly presented visual stimulus (Amassian et al., 1989). Methods A small checkerboard stimulus was briefly presented and subjects had to subsequently report which quadrant of the checkerboard was shown at reduced contrast (Fig. 1A). When TMS (MagVenture MagPro X100; MC-B70 coil) was applied to the left occipital pole at ∼100ms after checkerboard presentation, behavioral performance was reliably reduced (Fig. 1B). For each subject, the TMS timing and coil position resulting in the best suppression effect were determined in prior TMS-only experiments. Subsequently, using simultaneous EEG recordings, three conditions were tested: Combined “TMS&Visual” stimulation, “Visualonly” and “TMSonly”. A single experimental run lasted ∼4 min and contained trials of all conditions in a randomized order. 5 TMS intensities were tested, ranging from phosphene threshold to the intensity evoking chance level performance (or maximally 85% of max. stimulator output; Fig. 1B). The 5 intensities were tested in separate runs in a randomized order. Using several sessions, ∼120 trials were acquired for each condition at each intensity. EEG was recorded using a BrainAmp MR plus amplifier (Brain Products, Germany; 32 channels; impedances <5 kW) and analyzed using EEGLAB 6.01 (Delorme and Makeig, 2004). Pre-processing involved TMS artifact removal using polynomial interpolation, band-pass filtering (cutoff 0.1 & 50 Hz), baseline correction and eye blink rejection. The mean of the TMSonly trials was subtracted from the mean of the TMS&Visual trials to determine the TMS effect on the VEPs. Results Four subjects participated in the experiment. We analyzed EEG data within a left posterior region-of-interest (ROI). The checkerboard evoked reliable VEPs in all subjects (Fig. 2A). All subjects exhibited classical VEP patterns except for subject S4 whose P100 was absent. The timing of the TMS pulse with the strongest suppression corresponded to the N80 (S1 to S3) and the missing P100 (S4), respectively. In S1 to S3, the P100 increased monotonically for the 3 lower TMS intensities and leveled off for the 2 highest intensities, at which visual suppression occurred (Fig. 2B&C). The P100 exhibited the classical “paradoxical” lateralization over the right hemisphere (Fig. 3A; Towle et al., 1989). Interestingly, however, the modulation by TMS was consistently strongest for left posterior electrodes (Fig. 3B). In S4, the N150 increased for the first 4 intensities, and then decreased. Consistent to the results for S1 to S3, the modulation was strongest in left occipital electrodes. Conclusions The VEP modulation patterns hint towards a saturation effect taking place when TMS is strong enough to induce robust suppression. Future work involves dipole location to determine if the left-lateralized TMS effects on the P100 stem from a new source or from an orientation flip of the source underlying the classical P100 pattern.

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 Dates: 2009-07
 Publication Status: Published in print
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 Identifiers: DOI: 10.1016/S1053-8119(09)70313-1
BibTex Citekey: 6053
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Title: 15th Annual Meeting of the Organization for Human Brain Mapping (HBM 2009)
Place of Event: San Francisco, CA, USA
Start-/End Date: 2009-06-18 - 2009-06-23

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Title: NeuroImage
Source Genre: Journal
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Publ. Info: Orlando, FL : Academic Press
Pages: - Volume / Issue: 47 (Supplement 1) Sequence Number: - Start / End Page: S39 - S41 Identifier: ISSN: 1053-8119
CoNE: https://pure.mpg.de/cone/journals/resource/954922650166