Parametric study of transcranial alternating current stimulation for brain alpha power modulation.

Area of Science:

• Neuroscience
• Neurostimulation
• Brain Oscillations

Background:

• Transcranial alternating current stimulation (tACS) aims to modulate brain activity, specifically alpha power (8-12 Hz), linked to cognitive functions.
• Inconsistent stimulation parameters across studies hinder the establishment of reliable tACS protocols for alpha rhythm modulation.
• Optimizing tACS parameters is crucial for its effective application in research and clinical settings.

Purpose of the Study:

• To investigate the differential impact of tACS intensity, frequency, and stimulation site on alpha power modulation.
• To determine optimal parameters for reliable and persistent modulation of alpha oscillations using tACS.
• To compare the aftereffects of low versus high intensity tACS on alpha power.

Main Methods:

• Phase 1: 20 healthy participants received 20-minute tACS at either posterior (PO7-PO8) or anterior (F3-F4) sites, at individual alpha or theta frequency, or sham.
• Stimulation intensity was participant-dependent (≤ 6 mA) based on comfort.
• Phase 2: Participants tolerating higher intensities (4-6 mA) underwent 1 mA posterior alpha-frequency tACS to assess intensity-dependent modulation.

Main Results:

• Alpha-frequency tACS, particularly over posterior sites, increased alpha power more than theta-frequency or sham stimulation.
• Low-intensity (1 mA) posterior alpha-tACS showed similar immediate effects but superior sustained alpha power increase compared to high-intensity (4-6 mA) tACS up to 120 minutes post-stimulation.
• Posterior alpha-tACS preferentially modulated endogenous alpha oscillations in frontal and occipito-parietal regions.

Conclusions:

• Low-intensity (1 mA) posterior alpha-frequency tACS is a reliable and precise method for sustained modulation of alpha power.
• Higher tACS intensities are well-tolerated but less effective for inducing lasting changes in alpha oscillations.
• Posterior alpha-tACS offers a promising non-invasive approach for persistent modulation of frontal and occipito-parietal alpha activity.