Computational analysis shows why transcranial alternating current stimulation induces retinal phosphenes

Area of Science:

• Neuroscience
• Computational Biology
• Biophysics

Background:

• Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation technique.
• tACS modulates cortical oscillations and can induce subjective visual sensations known as phosphenes.
• The origin of tACS-induced phosphenes has been debated, with a need to understand their retinal or cortical basis.

Purpose of the Study:

• To computationally investigate the current flow from tACS electrodes to the eyes.
• To determine if tACS-induced phosphenes are of retinal origin.
• To analyze the sensitivity of the eye to electrical stimulation during tACS.

Main Methods:

• Utilized the finite-element method for head modeling.
• Created an anatomically realistic head model to simulate current pathways.
• Investigated various electrode montages for tACS.

Main Results:

• A portion of the tACS current flows through the eyes, depending on electrode placement.
• The retina is sensitive to electrical stimulation, leading to phosphenes even with distant electrodes.
• Computational modeling confirmed the retinal origin of tACS-induced phosphenes.

Conclusions:

• Retinal phosphene interference must be considered in tACS experimental design.
• Optimizing electrode locations, potentially using multiple reference electrodes, can minimize phosphenes.
• Computational modeling is valuable for guiding tACS electrode positioning to mitigate visual artifacts.