Université Bourgogne Franche-Comté, INSERM UMR1093-CAPS, UFR des Sciences du Sport, F-21078, Dijon, France.
Université Claude Bernard Lyon 1, CNRS, INSERM, Centre de Recherche en Neurosciences de Lyon CRNL U1028 UMR5292, PsyR2 Team, F-69500, Bron, France.
Cereb Cortex. 2023 Nov 27;33(23):11339-11353. doi: 10.1093/cercor/bhad370.
Dual-site transcranial magnetic stimulation has been widely employed to investigate the influence of cortical structures on the primary motor cortex. Here, we leveraged this technique to probe the causal influence of two key areas of the medial frontal cortex, namely the supplementary motor area and the medial orbitofrontal cortex, on primary motor cortex. We show that supplementary motor area stimulation facilitates primary motor cortex activity across short (6 and 8 ms) and long (12 ms) inter-stimulation intervals, putatively recruiting cortico-cortical and cortico-subcortico-cortical circuits, respectively. Crucially, magnetic resonance imaging revealed that this facilitatory effect depended on a key morphometric feature of supplementary motor area: individuals with larger supplementary motor area volumes exhibited more facilitation from supplementary motor area to primary motor cortex for both short and long inter-stimulation intervals. Notably, we also provide evidence that the facilitatory effect of supplementary motor area stimulation at short intervals is unlikely to arise from spinal interactions of volleys descending simultaneously from supplementary motor area and primary motor cortex. On the other hand, medial orbitofrontal cortex stimulation moderately suppressed primary motor cortex activity at both short and long intervals, irrespective of medial orbitofrontal cortex volume. These results suggest that dual-site transcranial magnetic stimulation is a fruitful approach to investigate the differential influence of supplementary motor area and medial orbitofrontal cortex on primary motor cortex activity, paving the way for the multimodal assessment of these fronto-motor circuits in health and disease.
双部位经颅磁刺激已被广泛用于研究皮质结构对初级运动皮质的影响。在这里，我们利用这项技术来探究内侧前额叶皮质的两个关键区域（辅助运动区和内侧眶额皮质）对初级运动皮质的因果影响。我们发现，辅助运动区刺激在短（6 和 8 毫秒）和长（12 毫秒）刺激间隔内促进初级运动皮质的活动，分别推测涉及皮质间和皮质下皮质间回路。至关重要的是，磁共振成像显示，这种促进作用取决于辅助运动区的一个关键形态特征：辅助运动区体积较大的个体，在短和长刺激间隔内，从辅助运动区到初级运动皮质的促进作用更大。值得注意的是，我们还提供了证据表明，短刺激间隔内辅助运动区刺激的促进作用不太可能来自同时来自辅助运动区和初级运动皮质的冲动的脊髓相互作用。另一方面，内侧眶额皮质刺激在短和长间隔内均适度抑制初级运动皮质的活动，而与内侧眶额皮质的体积无关。这些结果表明，双部位经颅磁刺激是一种研究辅助运动区和内侧眶额皮质对初级运动皮质活动的不同影响的有效方法，为健康和疾病中这些额运动回路的多模态评估铺平了道路。
