16.10.2025 New research conducted by a collaboration of ICTER scientists reveals how significantly the brain’s responses to light and electrical stimuli differ. These findings could contribute to developing more precise vision-restoring therapies, including transcorneal alternating current stimulation (tACS).
Can the eye be “tricked” with electric current into making the brain react as if it were seeing light? Can electrical impulses actually stimulate the visual system in a way comparable to natural visual stimulation? These are questions have guided the development of neurostimulation techniques used to treat eye diseases for years. Now, thanks to research conducted by a team of scientists from the International Centre for Eye Research (ICTER) and the Nencki Institute, it has been possible for the first time to compare the physiological responses of the brain to light and electrical stimulation in intricate detail, down to the layers of individual structures of the visual system.
The research, published in the journal Investigative Ophthalmology & Visual Science, was led by a team comprised of Dr. Katarzyna Kordecka and Dr. Andrzej T. Foik from ICTER, and Dr. Ewa Kublik from the Nencki Institute of Experimental Biology. The project was carried out as part of the international TRIO-Vi CoE project, funded by the European Commission Teaming for Excellence Program, the Foundation for Polish Science, and the National Science Centre.
“Until now, there has been much discussion about how electrical stimulation could enhance vision, but there has been a lack of concrete data showing what actually happens in the brain. Our study provides the first such detailed picture of how the visual system responds to electrical impulses – and shows that these are not random responses, but rather coherent and repetitive patterns of activity,” says Dr. Katarzyna Kordecka from ICTER.
What was the experiment like? Details from the lab
The aim of the study was to gain in-depth insight into how the visual system responds to two different types of stimulation: induced by light, or generated by electric current flowing through the cornea. The researchers constructed a comparative experimental model that enabled the recording and comparison of neural responses evoked by visual (VEP) or electrical (EEP) stimuli, within two anatomical structures crucial for visual processing: the superior colliculus (SC) and the primary visual cortex (V1).
The experiment was conducted on adult Wistar rats from the Medical University of Białystok, maintained under strictly controlled conditions at the Nencki Institute of Experimental Biology. Modern multichannel microelectrodes were used, enabling simultaneous recording of signals from different neural layers. For the superior colliculus, the superficial gray layer (SGS) and the visual layer (SO) were analyzed; and for the visual cortex, the supragranular (SG) and infragranular (IG) layers were analyzed. Using advanced current source density (CSD) analysis, the researchers were able to track current flow in the brain with high spatial and temporal precision.
Electrical stimulation was performed in two configurations: with electrodes placed on both eyes (eye-to-eye, E-E), and on both eyes and neck (eye-to-neck, E-N). Each configuration employed six pulse types: rectangular biphasic pulses (positive or negative onset), monophasic positive and negative pulses, and sinusoidal positive and negative pulses. Each stimulus type was repeated 300 times with random intervals between pulses, and all signals were recorded in parallel using a CED Power 1401 system and Spike2 software.
All collected data were standardized and analyzed comparatively, using the coefficient of determination R2 and analysis of response-peak latency and amplitude, among other methods, to assess the similarity of EEP and VEP waveforms. This parallel analysis allowed for comparisons not only of response strength and dynamics but also of their shape, spatial distribution, and repeatability. Finally, to verify that the electrodes were positioned precisely as planned, brain dissection and histological analysis were performed after the experiment using Nissl staining and DiI tracer, which allowed for the reconstruction of electrode paths and confirmed the reliability of the recording locations.
The brain reacts to light and electricity differently, but equally strongly
One of the most interesting findings was the observation that electrical impulses elicited responses of similar amplitude to light impulses, but with a much shorter time delay. This is because electrical stimulation bypasses phototransduction in the rods and cones, directly activating retinal ganglion cells, which send signals directly to subcortical structures and the visual cortex.
Although the electrical responses were strong and rapid, their shape differed significantly from light-evoked signals. Only in the E-E (eye-to-eye) configuration did EEP responses show partial similarity to VEPs, suggesting that electrode placement is fundamental to the spatial and functional distribution of brain activation. The greatest similarity between electrical and light responses was observed in the deep layers of the visual cortex, indicating that these areas may best replicate the “natural” signal-processing pathway.
The coefficient of determination R2 showed that in most cases, the waves induced by electrical stimulation are only partially similar to those induced by light, which is not necessarily a disadvantage. In the context of therapy, the goal is not always to perfectly replicate visual physiology, but rather to effectively activate the appropriate structures while maintaining safety and repeatability.
The study authors emphasize that their goal was not to create a substitute for vision but to understand the basic physiological mechanisms of brain activation using electrical current. Although previous clinical studies have suggested that transcorneal-alternating-current stimulation (tACS) can improve visual function in patients with glaucoma, retinitis pigmentosa, or optic nerve damage, it was unclear how exactly this stimulation works at the level of brain structures.
The results of the current study fill this gap. They show that even single electrical pulses – with appropriately selected shape and direction of flow – can activate the superior colliculus and the visual cortex in a repeatable manner, and with specific dynamics. The current not only affects the retina but also induces responses in central structures, which may be of great importance in the design of personalized neurostimulation therapies.
An impulse with therapeutic potential
Understanding how electricity affects different layers of the visual system can inspire new approaches to neurorehabilitation. This knowledge can be useful not only to guide treatment for retinal disorders, but also for damage to the visual cortex or visual pathways resulting from stroke, trauma, or neurodegenerative diseases.
Current stimulation – delivered in a precise manner based on knowledge of brain physiology – can support neuroplasticity, improve retinal blood flow, increase levels of neurotrophic growth factors, and even restore neural connections. But to make this possible, it is necessary to know which impulses work, how they work, where they act, and how long they last – precisely the aims of this study.
“Our research shows that the brain can process visual information not only through light. A properly selected electrical impulse can activate the same areas in a predictable and precise manner. This finding lays the foundation for future neuromodulation therapies that restore visual function,” explains Dr. Andrzej T. Foik, Group Leader of the OBI Group at ICTER.
In the future, such experiments could become the foundation for the development of intelligent therapeutic devices – implants, neurostimulation glasses, or personalized neuromodulation therapies – that will be both effective and precise.
Source: Katarzyna Kordecka, Ewa Kublik, Andrzej T. Foik (2025). Comparison of Physiological Brain Responses Evoked by Visual and Electrical Stimulation. Investigative Ophthalmology & Visual Science. DOI: https://doi.org/10.1167/iovs.66.5.1
Author: scientific editor Marcin Powęska
