Spatial Resolution of Phosphenes within the Visual Field using Non-Invasive Transcranial Alternating Current Stimulation

Non-Invasive Transcranial Alternating Current Stimulation (NITACS) is a method that applies weak electrical currents to the scalp or face to modulate brain activity. A fascinating application of NITACS is the induction of phosphenes — visual phenomena where individuals perceive light without external stimuli. These phosphenes have been observed and generated through various techniques, including direct electrical stimulation of the visual cortex. However, NITACS provides a non-invasive way to create these visual effects. This research aimed to understand the spatial resolution of NITACS-induced phosphenes, vital for visual aid technology and neuroscience. Eight healthy participants underwent NITACS with a novel electrode configuration on the face. Findings indicated that NITACS could induce phosphenes that showed spatially defined patterns in the visual field. The phosphene locations differed among participants but were consistently within the visual field. These patterns remained stable across repeated stimulations. Optimal parameters were determined for inducing vibrant phosphenes without discomfort. The study also identified electrode positions that moved phosphenes to various visual field regions. Receiver Operating Characteristics (ROC) analysis estimated specificity and sensitivity at 70.7% and 73.9%, respectively, with a control trial effectiveness of 98.4%. Overall, NITACS holds promise as a reliable non-invasive means to modulate visual perception.