Department of Medicine, University of Toronto, Toronto, Ontario, Canada.
School of Kinesiology, Brain Behavior Laboratory, University of Michigan, Ann Arbor, Michigan.
J Neurophysiol. 2021 Apr 1;125(4):1236-1250. doi: 10.1152/jn.00642.2020. Epub 2021 Feb 24.
The interconnection of the angular gyrus of right posterior parietal cortex (PPC) and the left motor cortex (LM1) is essential for goal-directed hand movements. Previous work with transcranial magnetic stimulation (TMS) showed that right PPC stimulation increases LM1 excitability, but right PPC followed by left PPC-LM1 stimulation (LPPC-LM1) inhibits LM1 corticospinal output compared with LPPC-LM1 alone. It is not clear if right PPC-mediated inhibition of LPPC-LM1 is due to inhibition of left PPC or to combined effects of right and left PPC stimulation on LM1 excitability. We used paired-pulse TMS to study the extent to which combined right and left PPC stimulation, targeting the angular gyri, influences LM1 excitability. We tested 16 healthy subjects in five paired-pulsed TMS experiments using MRI-guided neuronavigation to target the angular gyri within PPC. We tested the effects of different right angular gyrus (RAG) and LM1 stimulation intensities on the influence of RAG on LM1 and on influence of left angular gyrus (LAG) on LM1 (LAG-LM1). We then tested the effects of RAG and LAG stimulation on LM1 short-interval intracortical facilitation (SICF), short-interval intracortical inhibition (SICI), and long-interval intracortical inhibition (LICI). The results revealed that RAG facilitated LM1, inhibited SICF, and inhibited LAG-LM1. Combined RAG-LAG stimulation did not affect SICI but increased LICI. These experiments suggest that RAG-mediated inhibition of LAG-LM1 is related to inhibition of early indirect (I)-wave activity and enhancement of GABA receptor-mediated inhibition in LM1. The influence of RAG on LM1 likely involves ipsilateral connections from LAG to LM1 and heterotopic connections from RAG to LM1. Goal-directed hand movements rely on the right and left angular gyri (RAG and LAG) and motor cortex (M1), yet how these brain areas functionally interact is unclear. Here, we show that RAG stimulation facilitated right hand motor output from the left M1 but inhibited indirect (I)-waves in M1. Combined RAG and LAG stimulation increased GABA, but not GABA, receptor-mediated inhibition in left M1. These findings highlight unique brain interactions between the RAG and left M1.
右侧顶后叶角回（PPC）与左侧运动皮层（LM1）的连接对于目标导向的手部运动至关重要。先前使用经颅磁刺激（TMS）的研究表明，右侧 PPC 刺激会增加 LM1 的兴奋性，但与单独的 PPC-LM1 刺激相比，右侧 PPC 后紧接着左侧 PPC-LM1 刺激（LPPC-LM1）会抑制 LM1 皮质脊髓输出。目前尚不清楚右侧 PPC 介导的 LPPC-LM1 抑制是否是由于对左侧 PPC 的抑制，还是由于右侧和左侧 PPC 对 LM1 兴奋性的联合作用。我们使用成对脉冲 TMS 研究了针对角回的双侧 PPC 刺激在多大程度上影响 LM1 的兴奋性。我们使用 MRI 引导的神经导航在五个配对脉冲 TMS 实验中测试了 16 名健康受试者，以靶向 PPC 内的角回。我们测试了不同右侧角回（RAG）和 LM1 刺激强度对 RAG 对 LM1 的影响，以及左侧角回（LAG）对 LM1（LAG-LM1）的影响。然后，我们测试了 RAG 和 LAG 刺激对 LM1 短间隔内皮质内易化（SICF）、短间隔内皮质内抑制（SICI）和长间隔内皮质内抑制（LICI）的影响。结果表明，RAG 促进了 LM1，抑制了 SICF，并抑制了 LAG-LM1。联合 RAG-LAG 刺激并未影响 SICI，但增加了 LICI。这些实验表明，RAG 介导的 LAG-LM1 抑制与抑制早期间接（I）波活动和增强 LM1 中 GABA 受体介导的抑制有关。RAG 对 LM1 的影响可能涉及来自 LAG 的同侧连接到 LM1 和来自 RAG 的异位连接到 LM1。目标导向的手部运动依赖于右侧和左侧角回（RAG 和 LAG）和运动皮层（M1），但这些脑区如何相互作用尚不清楚。在这里，我们表明 RAG 刺激促进了左手 M1 的右手运动输出，但抑制了 M1 中的间接（I）波。联合 RAG 和 LAG 刺激增加了 GABA，但没有增加 GABA，受体介导的抑制在左侧 M1。这些发现强调了 RAG 和左侧 M1 之间独特的大脑相互作用。
