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This supplementary dataset is supportive of the randomized sham-controlled, double-blind, crossover clinical trial investigating polarity- and intensity-dependent effects of high-definition transcranial electrical stimulation (HD-tDCS) applied over the right temporo-parietal junction on mean middle cerebral artery blood flow velocity (MCA-BFv) bilaterally. Data of eleven healthy right-handed adults (6 women, 5 men; mean age 31 ± 5.6 years old) were analyzed for MCA-BFv, assessed using transcranial doppler ultrasound on the stimulated and the contralateral hemisphere concomitantly, during and after 3 blocks of 2 min HD-tDCS at 1, 2, and 3 mA. Participants received three electrical stimulation conditions (anode center, cathode center, and sham) randomly ordered across different days. The collected data is publicly available at Mendeley Data. This article and the data will inform future related investigations and safety analysis of transcranial non-invasive brain stimulation.

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Since neuronal activity is coupled with neurovascular activity, we aimed to analyze the cerebral blood flow hemodynamics during and following high-definition transcranial direct current stimulation (HD-tDCS). We assessed the mean middle cerebral artery blood flow velocity (MCA-BFv) bilaterally using transcranial doppler ultrasound, during and after HD-tDCS, in eleven right-handed healthy adult participants (6 women, 5 men; mean age 31 ± 5.6 years old), with no evidence of brain or cardiovascular dysfunction. The HD-tDCS electrode montage was centered over the right temporo-parietal junction. The stimulation protocol comprised 3 blocks of 2 min at each current intensity (1, 2, and 3 mA) and an inter-stimulus interval of 5 min between blocks. Participants received three electrical stimulation conditions (anode center, cathode center, and sham) on three different days, with an interval of at least 24 h. Stimulation was well tolerated across HD-tDCS conditions tested, and the volunteers reported no significant discomfort related to stimulation. There was no significant difference in the right or the left MCA-BFv during or after the stimulation protocol across all stimulation conditions. We conclude that at a range of intensities, vascular reaction assessed using middle cerebral artery blood flow is not significantly altered during or after HD-tDCS both locally and remotely, which provides further evidence for the safety of HD-tDCS.

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PURPOSE: We show a systematic review of known complications during intraoperative neuromonitoring (IONM) using transcranial electric stimulation motor evoked potentials (TES-MEP) on cervical spine surgery, which provides a summary of the main findings. A rare complication during this procedure, cardiac arrest by cardioinhibitory reflex, is also described. METHODS: Findings of 523 scientific papers published from 1995 onwards were reviewed in the following databases: CENTRAL, Cochrane Library, Embase, Google Scholar, Ovid, LILACS, PubMed, and Web of Science. This study evaluated only complications on cervical spine surgery undergoing TES-MEP IONM. RESULTS: The review of the literature yielded 13 studies on the complications of TES-MEP IONM, from which three were excluded. Five studies are case series; the rest are case reports. Overall, 169 complications on 167 patients were reported in a total of 38,915 patients, a global prevalence of 0.43%. The most common complication was tongue-bite in 129 cases, (76.3% of all complication events). Tongue-bite had a prevalence of 0.33% (CI 95%, 0.28-0.39%) in all patients on TES-MEP IONM. A relatively low prevalence of severe complications was found: cardiac-arrhythmia, bradycardia and seizure, the prevalence of this complications represents only one case in all the sample. Alongside, we report the occurrence of cardiac arrest attributable to TES-MEP IONM. CONCLUSIONS: This systematic review shows that TES-MEP is a safe procedure with a very low prevalence of complications. To our best knowledge, asystole is reported for the first time as a complication during TES-MEP IONM.

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Transcranial direct current stimulation (tDCS) is a re-emerging non-invasive brain stimulation technique that has been used in animal models and human trials aimed to elucidate neurophysiology and behavior interactions. It delivers subthreshold electrical currents to neuronal populations that shift resting membrane potential either toward depolarization or hyperpolarization, depending on stimulation parameters and neuronal orientation in relation to the induced electric field (EF). Although the resulting cerebral EFs are not strong enough to induce action potentials, spontaneous neuronal firing in response to inputs from other brain areas is influenced by tDCS. Additionally, tDCS induces plastic synaptic changes resembling long-term potentiation (LTP) or long-term depression (LTD) that outlast the period of stimulation. Such properties place tDCS as an appealing intervention for the treatment of diverse neuropsychiatric disorders. Although findings of clinical trials are preliminary for most studied conditions, there is already convincing evidence regarding its efficacy for unipolar depression. The main advantages of tDCS are the absence of serious or intolerable side effects and the portability of the devices, which might lead in the future to home-use applications and improved patient care. This chapter provides an up-to-date overview of a number tDCS relevant topics such as mechanisms of action, contemporary applications and safety. Furthermore, we propose ways to further develop tDCS research.

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