Mansouri Farrokh, Fettes Peter, Schulze Laura, Giacobbe Peter, Zariffa Jose, Downar Jonathan
Institute of Biomaterial and Biomedical Engineering, University of Toronto, Toronto, ON, Canada.
Institute of Medical Science, University of Toronto, Toronto, ON, Canada.
Front Neurosci. 2018 Dec 3;12:877. doi: 10.3389/fnins.2018.00877. eCollection 2018.
Non-invasive brain stimulation techniques are entering widespread use for the investigation and treatment of a range of neurological and neuropsychiatric disorders. However, most current techniques are 'open-loop', without feedback from target brain region activity; this limitation could contribute to heterogeneous effects seen for nominally 'inhibitory' and 'excitatory' protocols across individuals. More potent and consistent effects may ensue from closed-loop and, in particular, phase-locked brain stimulation. In this work, a closed-loop brain stimulation system is introduced that can analyze EEG data in real-time, provide a forecast of the phase of an underlying brain rhythm of interest, and control pulsed transcranial electromagnetic stimulation to deliver pulses at a specific phase of the target frequency band. The technique was implemented using readily available equipment such as a basic EEG system, a low-cost Arduino board and MATLAB scripts. The phase-locked brain stimulation method was tested in 5 healthy volunteers and its phase-locking performance evaluated at 0, 90, 180, and 270 degree phases in theta and alpha frequency bands. On average phase locking values of 0.55° ± 0.11° and 0.52° ± 0.14° and error angles of 11° ± 11° and 3.3° ± 18° were achieved for theta and alpha stimulation, respectively. Despite the low-cost hardware implementation, signal processing time generated a phase delay of only 3.8° for theta and 57° for alpha stimulation, both readily accommodated in the pulse trigger algorithm. This work lays the methodological steps for achieving phase-locked brain stimulation for brief-pulse transcranial electrical stimulation (tES) and repetitive transcranial magnetic stimulation (rTMS), facilitating further research on the effect of stimulation phase for these techniques.
非侵入性脑刺激技术正广泛应用于一系列神经和神经精神疾病的研究与治疗。然而，目前大多数技术都是“开环”的，没有来自目标脑区活动的反馈；这一局限性可能导致在个体间名义上的“抑制性”和“兴奋性”方案出现异质性效应。闭环，尤其是锁相脑刺激可能会产生更强且更一致的效果。在这项工作中，引入了一种闭环脑刺激系统，该系统可以实时分析脑电图（EEG）数据，预测感兴趣的潜在脑节律的相位，并控制脉冲经颅电磁刺激，在目标频段的特定相位发送脉冲。该技术使用诸如基本EEG系统、低成本的Arduino板和MATLAB脚本等现成设备来实现。在5名健康志愿者中测试了锁相脑刺激方法，并在θ和α频段的0、90、180和270度相位评估了其锁相性能。对于θ和α刺激，平均锁相值分别为0.55°±0.11°和0.52°±0.14°，误差角度分别为11°±11°和3.3°±18°。尽管硬件实现成本低，但信号处理时间仅为θ刺激产生了3.8°的相位延迟，为α刺激产生了57°的相位延迟，这两者都很容易被脉冲触发算法所接受。这项工作为实现用于短脉冲经颅电刺激（tES）和重复经颅磁刺激（rTMS）的锁相脑刺激奠定了方法学步骤，有助于进一步研究这些技术的刺激相位效应。
