Division of Functional and Restorative Neurosurgery, and Centre for Integrative Neuroscience, Eberhard Karls University Tuebingen, 72076 Tuebingen, Germany.
Cereb Cortex. 2018 Apr 1;28(4):1502-1515. doi: 10.1093/cercor/bhy016.
Rhythmic synchronization of neurons is known to affect neuronal interactions. In the motor system, oscillatory power fluctuations modulate corticospinal excitability. However, previous research addressing phase-specific gain modulation in the motor system has resulted in contradictory findings. It remains unclear how many time windows of increased responsiveness each oscillatory cycle provides. Moreover, we still lack conclusive evidence as to whether the motor cortex entails an intrinsic response modulation along the rhythm cycle, as shown for spinal neurons. We investigated this question with single-pulse transcranial magnetic stimulation over the primary motor cortex at rest. Application of near-motor threshold stimuli revealed a frequency- and phase-specific gain modulation at both cortical and spinal level, independent of the spontaneous oscillatory power fluctuations at each level. We detected bilateral sensorimotor circuits in the lower beta-band (14-17 Hz) and unilateral corticospinal circuits in the upper beta-band (20-24 Hz). These findings provide novel evidence that intrinsic activity in the human motor cortex modulates input gain along the beta oscillatory cycle within distinct circuits. In accordance with periodic alternations of synchronous hyper- and depolarization, increased neuronal responsiveness occurred once per oscillatory beta cycle. This information may lead to new brain state-dependent and circuit-specific interventions for targeted neuromodulation.
神经元的节律同步已知会影响神经元的相互作用。在运动系统中，振荡功率波动调节皮质脊髓兴奋性。然而，以前针对运动系统中特定相位增益调制的研究得出了相互矛盾的发现。目前尚不清楚每个振荡周期提供多少个响应增强的时间窗口。此外，我们仍然缺乏确凿的证据表明运动皮层是否沿着节律周期进行内在的响应调制，就像脊髓神经元那样。我们使用单脉冲经颅磁刺激在静息状态下对初级运动皮层进行了研究。应用接近运动阈值的刺激在皮层和脊髓水平均显示出频率和相位特异性的增益调制，而不受每个水平的自发振荡功率波动的影响。我们在较低的β波段（14-17 Hz）检测到双侧感觉运动回路，在上部β波段（20-24 Hz）检测到单侧皮质脊髓回路。这些发现提供了新的证据，表明人类运动皮层的固有活动在特定回路中沿着β振荡周期调节输入增益。与同步超极化和去极化的周期性交替一致，神经元的响应性增强每振荡β周期发生一次。这些信息可能会为有针对性的神经调节提供新的基于大脑状态和回路特异性的干预措施。
