Optimising Transcranial Electrical Stimulation for Visual Excitability
Transcranial electrical stimulation (tES) has garnered significant attention for its potential to modulate brain functions and alleviate symptoms in various psychiatric disorders. Specifically, tES targeting the occipital region (Oz) has shown promise in enhancing visual functions.
In a recent study, Wang et al. (2024) aimed to compare the effects of two tACS montages on occipital excitability, with a focus on optimising stimulation parameters using the Nurostym. They hypothesised that the Oz-Cz montage would result in better excitability and entrainment effects compared to the Oz-cheek montage.
The study, conducted using a single-blind sham-controlled crossover design, involved 10 healthy adult participants with normal or corrected-to-normal vision. The researchers measured pattern-reversal visual evoked potentials (VEP) to assess occipital responses before and after tACS stimulation. Two tACS montages—Oz-Cz and Oz-cheek—were compared, with sham stimulation included as a control.
Results indicated an immediate inhibitory effect of tACS on P100 amplitude, with the effect sustained for 20 minutes after stimulation in the Oz-Cz montage. However, tACS did not significantly affect N75 amplitude or P100 latency. Additionally, the entrainment effect, as measured by power spectral density (PSD) analysis, was inconclusive.
Wang et al. (2024) also evaluated subjective sensations and blinding effectiveness. Participants reported mild sensations such as stinging during active stimulation sessions, with no significant difference between montages. The blinding procedure was effective, ensuring unbiased participant responses.
While both montages produced similar effects on occipital excitability, they differed in terms of side effects and onset of action. The Oz-Cz montage resulted in fewer and milder side effects, while the Oz-cheek montage exhibited a faster onset of action and lower impedances.
Overall, the study highlights the importance of optimising stimulation parameters and electrode montages in tES interventions. The Nurostym provided a safe and non-invasive means of delivering tACS, offering insights into the potential of tES for enhancing visual excitability. Further research with larger sample sizes and double-blind designs is warranted to confirm these findings and explore the efficacy of tES in clinical populations.
References
Wang, J., Choi, K.Y. and Thompson, B. et al. (2024). The effect of montages of transcranial alternating current stimulation on occipital responses – a sham-controlled pilot study. Frontiers in Psychiatry 14. DOI: https://doi.org/10.3389/fpsyt.2023.1273044
