Machetanz Kathrin, Berelidze Levan, Guggenberger Robert, Gharabaghi Alireza
Institute for Neuromodulation and Neurotechnology, University of Tübingen, Tübingen, Germany.
Front Neurosci. 2021 Mar 15;15:632697. doi: 10.3389/fnins.2021.632697. eCollection 2021.
Transcutaneous auricular vagus nerve stimulation (taVNS) modulates brain activity and heart function. The induced parasympathetic predominance leads to an increase of heart rate variability (HRV). Knowledge on the corresponding cortical activation pattern is, however, scarce. We hypothesized taVNS-induced HRV increases to be related to modulation of cortical activity that regulates the autonomic outflow to the heart.
In thirteen healthy subjects, we simultaneously recorded 64-channel electroencephalography and electrocardiography during taVNS. Two taVNS stimulation targets were investigated, i.e., the cymba conchae and inner tragus, and compared to active control stimulation in the anatomical vicinity, i.e., at the crus helicis and outer tragus. We used intermitted stimulation bursts of 25 Hz applied at a periodicity of 1 Hz. HRV was estimated with different time-domain methodologies: standard deviation of RR (SDNN), the root mean squares of successive differences (RMSSD), the percentage of RR-intervals with at least 50 ms deviation from the preceding RR-interval (pNN50), and the difference of consecutive RR intervals weighted by their mean (rrHRV).
The stimulation-induced HRV increases corresponded to frequency-specific oscillatory modulation of different cortical areas. All stimulation targets induced power modulations that were proportional to the HRV elevation. The most prominent changes that corresponded to HRV increases across all parameters and stimulation locations were frontal elevations in the theta-band. In the delta-band, there were frontal increases (RMSSD, pNN50, rrHRV, SDNN) and decreases (SDNN) across stimulation sites. In higher frequencies, there was a more divers activity pattern: Outer tragus/crus helicis stimulation increased oscillatory activity with the most prominent changes for the SDNN in frontal (alpha-band, beta-band) and fronto-parietal (gamma-band) areas. During inner tragus/cymba conchae stimulation the predominant pattern was a distributed power decrease, particularly in the fronto-parietal gamma-band.
Neuro-cardiac interactions can be modulated by electrical stimulation at different auricular locations. Increased HRV during stimulation is correlated with frequency-specific increases and decreases of oscillatory activity in different brain areas. When applying specific HRV measures, cortical patterns related to parasympathetic (RMSSD, pNN50, rrHRV) and sympathetic (SDNN) modulation can be identified. Thus, cortical oscillations may be used to define stimulation locations and parameters for research and therapeutic purposes.
经皮耳迷走神经刺激（taVNS）可调节脑活动和心脏功能。所诱导的副交感神经优势导致心率变异性（HRV）增加。然而，关于相应的皮质激活模式的知识却很匮乏。我们假设taVNS诱导的HRV增加与调节心脏自主神经输出的皮质活动调节有关。
在13名健康受试者中，我们在taVNS期间同时记录了64通道脑电图和心电图。研究了两个taVNS刺激靶点，即耳甲艇和耳屏内侧，并与解剖学邻近部位的主动对照刺激进行比较，即耳轮脚和耳屏外侧。我们使用了以1Hz的周期施加的25Hz间歇性刺激脉冲串。用不同的时域方法估计HRV：RR间期的标准差（SDNN）、连续差值的均方根（RMSSD）、与前一个RR间期至少有50ms偏差的RR间期的百分比（pNN50）以及由其平均值加权的连续RR间期的差值（rrHRV）。
刺激诱导的HRV增加对应于不同皮质区域的频率特异性振荡调制。所有刺激靶点均诱导了与HRV升高成比例的功率调制。在所有参数和刺激部位中，与HRV增加相对应的最显著变化是θ波段的额叶功率升高。在δ波段，刺激部位的额叶功率有增加（RMSSD、pNN50、rrHRV、SDNN）和降低（SDNN）。在较高频率下，活动模式更为多样：耳屏外侧/耳轮脚刺激增加了振荡活动，在额叶（α波段、β波段）和额顶叶（γ波段）区域，对SDNN的变化最为显著。在耳屏内侧/耳甲艇刺激期间，主要模式是分布式功率降低，特别是在额顶叶γ波段。
神经 - 心脏相互作用可通过不同耳部位置的电刺激进行调节。刺激期间HRV的增加与不同脑区振荡活动的频率特异性增加和降低相关。当应用特定的HRV测量方法时，可以识别与副交感神经（RMSSD、pNN50、rrHRV）和交感神经（SDNN）调制相关的皮质模式。因此，皮质振荡可用于确定研究和治疗目的的刺激位置和参数。
