The effect of TMS over hMT+ during a visual adaptation task

Abstract TMS effects depend on the state of underlying neuronal populations: e.g. MEPs are easier to evoke during active contraction than during rest (Siebner, 2022). This state dependence was also reported for sensory priming and adaptation, where TMS cancels their effects. For instance, in a motion detection task, participants fail to detect direction more often for the adapted direction (seen during 60seconds pre-test). Cattaneo and Silvanto (2008) reported that single-pulse TMS over the hMT+ visual area reversed the adaptation effect, demonstrating TMS state dependence and that neuronal populations in hMT+ code the attribute ‘direction’. Here, we used the same design to probe state dependency. Eight participants reported direction (left/right) of moving dots. Before test trials, participants adapted to one direction (left/right) during 60seconds. Each adaptation block was followed by 24 test trials (83ms). This was repeated four times for both TMS and no-TMS conditions. Single-pulse TMS (intensity: 61.0±6.2%MSO) was applied over left hMT+ at the beginning of each trial (Magventure X100, butterfly-coil). hMT+ was localized via fMRI-neuronavigation (n=3) or phosphenes. The adaptation phenomenon using this stimulus was proven before the TMS experiment (n=11, paired t-test, p=0.006). Here, participants’ performance was also lower for the adapted direction (hit-rate 0.64±0.13) than for the non-adapted (hit-rate 0.80±0.14). However, TMS failed to cancel the adaptation effect: hit-rate for the adapted direction without TMS (0.64±0.13) was kept similar in the TMS condition (0.64±0.12) (Wilcoxon z=-0.169, p=0.866). The state dependency feature for TMS over hMT+ was not observed when participants adapted to a given direction. However, TMS effects depend not only on the physiological state but also on the neurons geometry in relation to the TMS-induced electric field. Future work considering functional data and anatomical arrangement may elucidate how coil orientation influences the targeting of adapted neural populations. Research Category and Technology and Methods Basic Research: 10. Transcranial Magnetic Stimulation (TMS) Keywords: state-dependecy, TMS, hMT, adaptation