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Retinal and Cortical Contributions to Phosphenes During Transcranial Electrical Current Stimulation
Ian D Evans1,2,3,4, Stephen Palmisano1,2, Rodney J Croft1,2,3,4
1School of Psychology, University of Wollongong, Wollongong, Australia.
Bioelectromagnetics
|January 13, 2021
Summary
Transcranial electric current stimulation (tECS) can induce phosphenes, visual sensations perceived as light flashes. This study suggests that while retinal activation contributes, the visual cortex in the occipital lobe also plays a role in tECS-induced phosphene perception.
Area of Science:
- Neuroscience
- Bioelectromagnetics
- Sensory Perception
Background:
- Phosphenes induced by transcranial electric current stimulation (tECS) are often attributed to retinal activation.
- The precise origin of tECS-induced phosphenes, particularly concerning the visual cortex, remains undetermined.
Purpose of the Study:
- To investigate whether prefrontal regions (e.g., retina) contribute to tECS-induced phosphenes using an FPz-Oz montage compared to an Oz-Cz montage.
- To determine if the occipital lobe's visual cortex contributes to tECS-induced phosphenes by comparing FPz-Oz and FPz-Cz montages.
Main Methods:
- Phosphene detection thresholds were measured in 22 participants across various tECS frequencies (6–32 Hz) using different electrode montages (FPz-Oz, Oz-Cz, FPz-Cz).
- Current density at the retina and occipital lobe was modeled across 20 head models at phosphene thresholds for each montage.
Main Results:
- Increased current density near the retina (FPz-Oz vs. Oz-Cz) lowered phosphene thresholds, supporting retinal involvement.
- Increased current density near the occipital cortex (FPz-Oz vs. FPz-Cz) also lowered phosphene thresholds, indicating visual cortex contribution.
- Modeling suggested that occipital cortex stimulation required less retinal current density for phosphene perception.
Conclusions:
- tECS-induced phosphenes likely result from a combination of retinal and visual cortex activation.
- The findings challenge the sole reliance on retinal activation as the explanation for tECS-induced phosphenes.
- Stimulation of the occipital cortex appears to be a significant factor in the perception of tECS-induced phosphenes.
