Towards assessing patient eligibility for optical neural interfaces: a simulation approach

Optical neural interfaces (ONIs) offer a promising, non-invasive alternative to electrical neural interfaces, especially those based on functional near-infrared spectroscopy (fNIRS), but their performance is affected by biological factors such as skin pigmentation and hair texture, leading to potential exclusion of diverse populations. This project aimed to investigate how varying wavelengths, melanin concentrations, and incidence angles affect light penetration in tissues of the head, using Monte Carlo simulations. Monte Carlo simulations were done on a six-layer slab mode (epidermis, dermis, skull, Cerebral Spinal fluid, grey matter and white matter), across six concentrations of melanin on the Fitzpatrick scale, across wavelengths spanning 500- 1000 nm and angles 90°, 60°, 45°, 30°. Results demonstrated that higher melanin concentrations significantly attenuate photon penetration, particularly at lower wavelengths, and that oblique incidence angles further limit light delivery to deeper tissues. Wavelengths in the longer NIR range improved penetration depth across all melanin types. This study highlights the importance of wavelength selection, angle of incidence when developing ONIs to ensure equitable performance across diverse patient populations. The framework developed here could inform better eligibility assessments and promote equitable neurotechnology applications across diverse populations.