Non-invasive Brain Stimulation Unit, Department of Behavioral and Clinical Neurology, Santa Lucia Foundation IRCCS, Rome, Italy.
Centre for Medical Image Computing, University College London, London, UK.
Neuroimage. 2018 Jul 15;175:365-378. doi: 10.1016/j.neuroimage.2018.04.011. Epub 2018 Apr 7.
Since early days after stroke, the brain undergoes a complex reorganization to allow compensatory mechanisms that promote functional recovery. However, these mechanisms are still poorly understood and there is urgent need to identify neurophysiological markers of functional recovery after stroke. Here we aimed to track longitudinally the time-course of cortical reorganization by measuring for the first time EEG cortical activity evoked by TMS pulses in patients with subcortical stroke. Thirteen patients in the sub-acute phase of ischemic subcortical stroke with motor symptoms completed the longitudinal study, being evaluated within 20 days and after 40, 60 and 180 days after stroke onset. For each time-point, EEG cortical activity evoked by single TMS pulses was assessed over the motor and parietal cortex of the affected and unaffected hemisphere. We evaluated global TMS-evoked activity and TMS-evoked oscillations in different frequency bands. These measurements were paralleled with clinical and behavioral assessment. We found that motor cortical activity measured by TMS-EEG varied across time in the affected hemisphere. An increase of TMS-evoked activity was evident at 40 days after stroke onset. Moreover, stroke patients showed a significant increase in TMS-evoked alpha oscillations, as highlighted performing analysis in the time-frequency domain. Notably, these changes indicated that crucial mechanisms of cortical reorganization occur in this short-time window. These changes coincided with the clinical improvement. TMS-evoked alpha oscillatory activity recorded at baseline was associated to better functional recovery at 40 and 60 days' follow-up evaluations, suggesting that the power of the alpha rhythm can be considered a good predictor of motor recovery. This study demonstrates that cortical activity increases dynamically in the early phases of recovery after stroke in the affected hemisphere. These findings point to TMS-evoked alpha oscillatory activity as a potential neurophysiological markers of stroke recovery and could be helpful to determine the temporal window in which neuromodulation should be potentially able to drive neuroplasticity in an effective functional direction.
自中风后早期开始，大脑经历了一个复杂的重组过程，以促进功能恢复的代偿机制。然而，这些机制仍然知之甚少，迫切需要确定中风后功能恢复的神经生理标志物。在这里，我们旨在通过首次测量皮质下中风患者经颅磁刺激脉冲诱发的 EEG 皮质活动来跟踪皮质重组的时间过程。13 名处于缺血性皮质下中风亚急性期且有运动症状的患者完成了纵向研究，在中风发作后 20 天内以及 40、60 和 180 天内进行了评估。对于每个时间点，评估了受影响和未受影响半球的单个 TMS 脉冲诱发的 EEG 皮质活动。我们评估了全局 TMS 诱发的活动和不同频段的 TMS 诱发的振荡。这些测量与临床和行为评估并行进行。我们发现，TMS-EEG 测量的运动皮质活动在受影响的半球随时间变化。在中风发作后 40 天，TMS 诱发的活动明显增加。此外，中风患者在 TMS 诱发的α振荡中表现出显著增加，如在时频域中进行分析所强调的那样。值得注意的是，这些变化表明皮质重组的关键机制发生在这个短时间窗口内。这些变化与临床改善相吻合。在基线记录的 TMS 诱发的α振荡活动与 40 和 60 天随访评估时的更好功能恢复相关，表明α节律的功率可以被认为是运动恢复的良好预测指标。这项研究表明，在受影响的半球中，中风后恢复的早期阶段皮质活动动态增加。这些发现指向 TMS 诱发的α振荡活动作为中风恢复的潜在神经生理标志物，并可能有助于确定潜在的神经调节能够以有效的功能方向驱动神经可塑性的时间窗口。
