Biology subjects

Silvanto, J.

Publications and source records attributed to Silvanto, J..

2 recordsLinked to original sources

bioRxiv2017

On mechanisms of Transcranial Magnetic Stimulation (TMS): How brain state and baseline performance level determine behavioral effects of TMS

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. 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 nonlinear neural effects, underlie behavioral effects of TMS.

neuroscience↗

bioRxiv2017

Common framework for virtual lesion and state-dependent TMS: the facilitatory/suppressive range model of online TMS effects on behavior

The behavioral effects of Transcranial Magnetic Stimulation (TMS) are often nonlinear; factors such as stimulation intensity and brain state can modulate the impact of TMS on observable behavior in qualitatively different manner. Here we propose a theoretical framework to account for these effects. In this model, there are distinct intensity ranges for facilitatory and suppressive effects of TMS: low intensities facilitate neural activity and behavior whereas high intensities induce suppression. The key feature of the model is that these ranges are shifted by changes in neural excitability: consequently, a TMS intensity, which normally induces suppression, can have a facilitatory effect if the stimulated neurons are being inhibited. For example, adaptation reduces excitability of adapted neurons; the outcome is that TMS intensities which inhibit non-adapted neurons induce a facilitation on adapted neural representations, leading to reversal of adaptation effects. In conventional virtual lesion paradigms, similar effects occur because neurons not tuned to the target stimulus are inhibited. The resulting reduction in excitability can turn high intensity inhibitory TMS to low intensity facilitatory TMS for these neurons (whereas neurons tuned to the target stimulus are inhibited), leading to a reduction in signal-to-noise ratio. Thus differential excitability levels of neural populations contributing to behavior, combined with nonlinear neural effects, can explain how TMS modulates behavior.

neuroscience↗