Transcranial Electrical Stimulation (tES)*

Transcranial Electrical Stimulation (tES) is a scientifically validated, non-invasive neuromodulation technique employing low-intensity electrical currents delivered via scalp electrodes. It is extensively researched for its therapeutic potential and cognitive enhancement capabilities, grounded in established neurophysiological principles. tES provides targeted modulation of neuronal activity, facilitating exploration into cortical dynamics and the treatment of various neurological conditions.

Main Types of tES:

1. Transcranial Direct Current Stimulation (tDCS)
   • Current Type: Constant, direct current.
   • Mechanism: Anodal (positive) stimulation increases neuronal excitability via depolarization, while cathodal (negative) stimulation decreases excitability via hyperpolarization (Nitsche & Paulus, 2000).
   • Applications: Depression treatment, cognitive enhancement, motor rehabilitation (Nitsche & Paulus, 2000; Lefaucheur et al., 2017).
2. Transcranial Random Noise Stimulation (tRNS)
   • Current Type: Randomized electrical frequencies (0.1–640 Hz).
   • Mechanism: Enhances cortical excitability through stochastic resonance, enabling diffuse cortical modulation without significant lateralization (Terney et al., 2008; Kadosh et al., 2010).
   • Applications: Motor learning enhancement, improvements in numerical cognition, and memory consolidation (Kadosh et al., 2010; Snowball et al., 2013).
3. Transcranial Alternating Current Stimulation (tACS)
   • Current Type: Sinusoidal alternating current.
   • Mechanism: Frequency-specific cortical modulation through entrainment of endogenous brain oscillations, influencing neuronal synchronization patterns (Antal & Herrmann, 2018).
   • Applications: Memory consolidation, attentional enhancement, decision-making improvements (Antal & Herrmann, 2018; Herrmann et al., 2013).
4. Temporal Interference (TI)
   • Current Type: Multiple high-frequency currents creating interference patterns at lower frequencies within deep brain structures.
   • Mechanism: Noninvasive, focal stimulation of deeper cortical and subcortical regions without significantly activating superficial tissues (Grossman et al., 2017).
   • Applications: Experimental studies focused on deep brain modulation and disorders requiring deep cortical targeting (Grossman et al., 2017).
5. Electrical Vestibular Stimulation (EVS)
   • Current Type: Alternating or direct currents applied to vestibular nerves.
   • Mechanism: Activation of vestibular pathways that modulate balance, spatial orientation, and posture through vestibulo-cortical networks (Fitzpatrick & Day, 2004).
   • Applications: Vestibular disorders treatment, balance enhancement, posture correction (Fitzpatrick & Day, 2004).

Safety and Considerations:

• Generally considered safe when guidelines for intensity (typically ≤2 mA) and stimulation duration (usually ≤30 min) are strictly followed.
• Potential side effects are typically mild and transient, including temporary skin irritation, dizziness, mild headaches, or phosphene phenomena.
• Contraindicated for individuals with epilepsy or implanted electronic medical devices (Brunoni et al., 2011).

Key Benefits of tES:

• Non-invasive and painless application.
• Demonstrated efficacy in enhancing cognitive, motor, and perceptual functions.
• Established therapeutic utility in neurological and psychiatric conditions, supported by rigorous scientific research.

References:

• Nitsche, M. A., & Paulus, W. (2000). Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation. Journal of Physiology, 527(3), 633–639.
• Lefaucheur, J. P., et al. (2017). Evidence-based guidelines on the therapeutic use of transcranial direct current stimulation (tDCS). Clinical Neurophysiology, 128(1), 56–92.
• Terney, D., Chaieb, L., Moliadze, V., Antal, A., & Paulus, W. (2008). Increasing human brain excitability by transcranial high-frequency random noise stimulation. Journal of Neuroscience, 28(52), 14147–14155.
• Kadosh, R. C., Soskic, S., Iuculano, T., Kanai, R., & Walsh, V. (2010). Modulating neuronal activity produces specific and long-lasting changes in numerical competence. Current Biology, 20(22), 2016–2020.
• Snowball, A., et al. (2013). Long-term enhancement of brain function and cognition using cognitive training and brain stimulation. Current Biology, 23(11), 987–992.
• Antal, A., & Herrmann, C. S. (2018). Transcranial Alternating Current and Random Noise Stimulation: Possible Mechanisms. Neural Plasticity, 2018, Article ID 3616809.
• Herrmann, C. S., Rach, S., Neuling, T., & Strüber, D. (2013). Transcranial alternating current stimulation: a review of the underlying mechanisms and modulation of cognitive processes. Frontiers in Human Neuroscience, 7, 279.
• Grossman, N., Bono, D., Dedic, N., Kodandaramaiah, S. B., Rudenko, A., Suk, H. J., Cassara, A. M., Neufeld, E., Kuster, N., Tsai, L. H., Pascual-Leone, A., & Boyden, E. S. (2017). Noninvasive Deep Brain Stimulation via Temporally Interfering Electric Fields. Cell, 169(6), 1029–1041.e16.
• Fitzpatrick, R. C., & Day, B. L. (2004). Probing the human vestibular system with galvanic stimulation. Journal of Applied Physiology, 96(6), 2301–2316.
• Brunoni, A. R., et al. (2011). Clinical research with transcranial direct current stimulation (tDCS): challenges and future directions. Brain Stimulation, 5(3), 175–195.

It's crucial for researchers to understand the regulatory requirements associated with tES devices and to follow the guidelines for their appropriate use. This is particularly relevant in the United States, where such devices are regulated by the FDA. Compliance ensures ethical and safe use aligned with current regulatory standards.

Research Use Only: Researchers must recognize that tES devices are strictly intended for research applications unless explicitly cleared or approved by the FDA for clinical or diagnostic purposes.

Ethical and Safety Considerations: tES-related research must comply with rigorous ethical and safety standards, including securing Institutional Review Board (IRB) approval and obtaining informed consent from participants. Researchers should clearly inform participants about the experimental nature of the devices used.