Monitoring Cortical Response and Electrode-Retina Impedance Under Epiretinal Stimulation in Rats

Liquid-metal-based three-dimensional microelectrode arrays integrated with implantable ultrathin retinal prosthesis for vision restoration

Electronic retinal prostheses for stimulating retinal neurons are promising for vision restoration. However, the rigid electrodes of conventional retinal implants can inflict damage on the soft retina tissue. They also have limited selectivity due to their poor proximity to target cells in the degenerative retina. Here we present a soft artificial retina (thickness, 10 μm) where flexible ultrathin photosensitive transistors are integrated with three-dimensional stimulation electrodes of eutectic gallium-indium alloy. Platinum nanoclusters locally coated only on the tip of these three-dimensional liquid-metal electrodes show advantages in reducing the impedance of the stimulation electrodes. These microelectrodes can enhance the proximity to the target retinal ganglion cells and provide effective charge injections (72.84 mC cm-2) to elicit neural responses in the retina. Their low Young's modulus (234 kPa), owing to their liquid form, can minimize damage to the retina. Furthermore, we used an unsupervised machine learning approach to effectively identify the evoked spikes to grade neural activities within the retinal ganglion cells. Results from in vivo experiments on a retinal degeneration mouse model reveal that the spatiotemporal distribution of neural responses on their retina can be mapped under selective localized illumination areas of light, suggesting the restoration of their vision.

Effect of the Aperiodic Electrical Stimulation on the Visual Cortical Neuronal Response. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2023;2023:1-4. [PMID: 38083157 DOI: 10.1109/embc40787.2023.10341193] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In patients with retinal degenerative illnesses such as retinitis pigmentosa and age-related macular degeneration, retinal prosthesis shows the potential to restore partial vision. The natural stimuli are the aperiodic events distributed across a short time span. However, most studies commonly used periodic stimulation. Even though some in vitro studies explored the effect of aperiodic retinal stimulation on the retina ganglion cells' membrane potential, it still needs to understand how the aperiodic electrical stimulation on the retina affects the response in visual cortex. This study investigated how aperiodic retinal stimulation affects the electrically evoked cortical response compared with periodic stimulation in Sprague Dawley (SD) rats. We found that the aperiodic retinal stimulation evoked a significantly higher spike rate than the periodic pattern, especially at high frequencies (10 and 20 Hz). The spike rates showed a more significant difference between the periodic and 10% noise stimulation (P = 0.0013 at 20 Hz, two-tailed paired t-test) at 20 Hz stimulation. Regarding the temporal precision of responses, the responses to aperiodic stimulation showed higher temporal precision compared to periodic stimulation. The response to some stimulation pulse numbers under 10 and 20 Hz 50% noise and Poisson pattern stimulation was higher than the response to the first pulse. However, at the same frequency, the response to some stimulation pulse numbers under periodic stimulation was lower than the response to the first pulse. These findings raised a possible way to increase the response level and the temporal precision of the electrically evoked response.Clinical Relevance- This suggests that using aperiodic stimulation in retinal prostheses can increase electrically evoked response levels and temporal precision.