TMS Poster OnlyEffects of TMS on visual evoked potentials in a visual suppression task
Section snippets
Method:
In 3 subjects, VEPs were reliably induced by a small checkerboard stimulus briefly presented in the parafoveal lower right quadrant (Fig. 1B). Subjects S1 and S2 had classical VEP patterns, in S3 the P100 was missing. A random quadrant of the checkerboard was shown at reduced contrast. Subjects had to identify and report it by a button-press. TMS was applied to the left occ. pole (MagVenture MagPro X100; MC-B70 coil). The best TMS timing and coil position were determined in pretests. The timing
Result:
In S1 and S2, the P100 increased monotonically for the 3 lower TMS intensities (Fig. 1C&D) and leveled off for the 2 highest intensities, at which visual suppression occurred (Fig. 1A). In S3, the N150 increased for the first 4 intensities, and then decreased. Similar modulations occured for the N150 in S1 and S2 and the “P200” in S3 (data not shown).
Conclusion:
The VEP modulation patterns hint towards a saturation effect taking place when TMS is strong enough to induce robust suppression. Future work involves testing a further subject to confirm the modulation effects, and the systematic variation of the TMS SOA.