Motor cortex rTMS modulates adult ocular dominance plasticity

Well-established evidence supports cross-modal interactions of sensory brain plasticity. Here, we extend cross-modality beyond the boundaries of sensory regions and provide first-time evidence in adult healthy humans that motor plasticity influences homeostatic visual plasticity. To this end, we employed repetitive transcranial magnetic stimulation (rTMS), known to modulate the excitation/inhibition balance in the primary motor cortex (M1), while examining the impact of this intervention on ocular dominance plasticity induced by short-term monocular deprivation (MD). Specifically, participants completed, in counterbalanced order, two neuromodulation sessions delivering either Active or Sham rTMS (10 Hz, 1600 pulses), during a 90-min MD period. We show that Active but not Sham rTMS significantly increased amplitudes of peak-to-peak motor evoked potentials, confirming facilitatory cortico-spinal after-effects driven by M1 stimulation. While robust ocular dominance shifts were observed for both rTMS conditions, greater increases of cortico-spinal excitability scaled with smaller ocular dominance shifts, suggesting interference of primary visual cortex plasticity ensuing a modulation of M1 excitability and competitive interactions between motor and visual plasticity. These results hint at global homeostatic mechanisms governing adult cortical plasticity across distant networks and highlight the need to consider cross-modal interactions between motor and visual systems when designing learning and rehabilitation strategies for adults.