On the Mechanisms of Transcranial Magnetic Stimulation (TMS): How Brain State and Baseline Performance Level Determine Behavioral Effects of TMS.

Juha Silvanto,Marco Marelli,Silvia Bona,Zaira Cattaneo

doi:10.3389/fpsyg.2018.00741

Abstract

The behavioral effects of Transcranial Magnetic Stimulation (TMS) can change qualitatively when stimulation is preceded by initial state manipulations such as priming or adaptation. In addition, baseline performance level of the participant has been shown to play a role in modulating the impact of TMS. Here we examined the link between these two factors. This was done using data from a previous study using a TMS-priming paradigm, in which, at group level, TMS selectively facilitated targets incongruent with the prime while having no statistically significant effects on other prime-target congruencies. Correlation and linear mixed-effects analyses indicated that, for all prime-target congruencies, a significant linear relationship between baseline performance and the magnitude of the induced TMS effect was present: low levels of baseline performance were associated with TMS-induced facilitations and high baseline performance with impairments. Thus as performance level increased, TMS effects turned from facilitation to impairment. The key finding was that priming shifted the transition from facilitatory to disruptive effects for targets incongruent with the prime, such that TMS-induced facilitations were obtained until a higher level of performance than for other prime-target congruencies. Given that brain state manipulations such as priming operate via modulations of neural excitability, this result is consistent with the view that neural excitability, coupled with non-linear neural effects, underlie behavioral effects of TMS.

Highlights

Single pulses of Transcranial Magnetic Stimulation (TMS) applied concurrently with a visual target can either facilitate or impair detection performance, depending on factors such as stimulation intensity and brain state (Silvanto et al, 2008, 2017)
For all prime-target congruencies, correlation (Pearson’s r) between baseline performance and the TMS effect was significant (Fully congruent: r = −0.741, p = 0.001; fully incongruent: r = −0.814; p < 0.001; color congruent: r = −0.772; p < 0.001; orientation congruent: r = −0.703; p = 0.002). These indicate a negative relationship between baseline level of performance and the TMS effect, such that low baseline performance is associated with a facilitatory effect of TMS and high baseline performance with impairments
Our findings indicate that baseline performance level and initial brain state combine to produce behavioral effects of TMS

Summary

Introduction

Single pulses of Transcranial Magnetic Stimulation (TMS) applied concurrently with a visual target can either facilitate or impair detection performance, depending on factors such as stimulation intensity and brain state (Silvanto et al, 2008, 2017). Whereas TMS intensities above phosphene threshold have been found to mask visual perception when applied over the early. Non-linear effects are observed when TMS is applied during a behavioral task following an initial state manipulation such as adaptation or priming. In a study using orientation-contingent color priming, suprathreshold TMS (applied within the TMS-masking time window) was found to induce a facilitatory effect on items incongruent with the prime, with no effects on other prime-target congruencies (Silvanto et al, 2017). Manipulations of initial activation state qualitatively change the nature of behavioral TMS effects

Methods

Results

Conclusion