Exp ORL, Department of Neurosciences, The Leuven Brain Institute, KU Leuven, Belgium.
Experimental Neurosurgery and Neuroanatomy, Department of Neurosciences, KU Leuven, Belgium.
Brain Stimul. 2024 May-Jun;17(3):648-659. doi: 10.1016/j.brs.2024.05.005. Epub 2024 May 11.
Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation method that can modulate many brain functions including learning and memory. Recent evidence suggests that tDCS memory effects may be caused by co-stimulation of scalp nerves such as the trigeminal nerve (TN), and not the electric field in the brain. The TN gives input to brainstem nuclei, including the locus coeruleus that controls noradrenaline release across brain regions, including hippocampus. However, the effects of TN direct current stimulation (TN-DCS) are currently not well understood.
In this study we tested the hypothesis that stimulation of the trigeminal nerve with direct current manipulates hippocampal activity via an LC pathway.
We recorded neural activity in rat hippocampus using multichannel silicon probes. We applied 3 min of 0.25 mA or 1 mA TN-DCS, monitored hippocampal activity for up to 1 h and calculated spikes-rate and spike-field coherence metrics. Subcutaneous injections of xylocaine were used to block TN, while intraperitoneal and intracerebral injection of clonidine were used to block the LC pathway.
We found that 1 mA TN-DCS caused a significant increase in hippocampal spike-rate lasting 45 min in addition to significant changes in spike-field coherence, while 0.25 mA TN-DCS did not. TN blockage prevented spike-rate increases, confirming effects were not caused by the electric field in the brain. When 1 mA TN-DCS was delivered during clonidine blockage no increase in spike-rate was observed, suggesting an important role for the LC-noradrenergic pathway.
These results support our hypothesis and provide a neural basis to understand the tDCS TN co-stimulation mechanism. TN-DCS emerges as an important tool to potentially modulate learning and memory.
经颅直流电刺激（tDCS）是一种非侵入性的神经调节方法，可以调节包括学习和记忆在内的许多大脑功能。最近的证据表明，tDCS 的记忆效应可能是由于三叉神经（TN）等头皮神经的共同刺激引起的，而不是大脑中的电场。TN 向包括蓝斑核在内的脑干核团提供输入，蓝斑核控制包括海马体在内的大脑区域的去甲肾上腺素释放。然而，目前对 TN 直流电刺激（TN-DCS）的影响还不太了解。
在这项研究中，我们测试了以下假设：用直流电刺激三叉神经通过 LC 通路来调节海马体的活动。
我们使用多通道硅探针记录大鼠海马体的神经活动。我们施加 3 分钟的 0.25mA 或 1mA 的 TN-DCS，监测海马体活动长达 1 小时，并计算出尖峰率和尖峰场相干性指标。皮下注射盐酸利多卡因用于阻断 TN，而腹腔内和脑内注射可乐定用于阻断 LC 通路。
我们发现，1mA 的 TN-DCS 导致海马体尖峰率显著增加，持续 45 分钟，此外尖峰场相干性也发生显著变化，而 0.25mA 的 TN-DCS 则没有。TN 阻断防止了尖峰率的增加，证实这些影响不是由大脑中的电场引起的。当在可乐定阻断期间施加 1mA 的 TN-DCS 时，没有观察到尖峰率的增加，这表明 LC-去甲肾上腺素能通路起着重要作用。
这些结果支持我们的假设，并为理解 tDCS-TN 共同刺激机制提供了神经基础。TN-DCS 作为一种潜在调节学习和记忆的重要工具出现。
