Neurostimulation devices to treat Alzheimer’s disease

" In brief, the main shortcoming of the EMF experimental results regarding the biological effects of radiofrequency exposures is the consistency and inconsistencies between the results of the animal and human studies. This is explained by the difference in frequencies, penetration depth, tissue’s dielectric properties, mass density, and complex 3-D E-field distribution, all of which affect the energy absorbed or power deposition on the tissues [206, 207]. The SAR measures the energy absorbed or power deposition in the tissues relevant to specific biological effects. Therefore, it is a central consideration for EMF therapy simulations [208–211]. We cannot determine the SAR only via input power-based estimation due to its dependence on these factors. A crucial factor in the EMF and biological interaction in humans is penetration depth; the penetration depth decreases when frequency increases, which gives the skin depth within which 63% of the energy is deposited. Other important factors are the conductivity and permittivity of the tissues, as they determine how much electromagnetic radiation is absorbed by the body, with higher conductivity and permittivity leading to greater absorption; essentially, these properties dictate how readily electric fields can penetrate and interact with tissue at different frequencies, depending on the tissue type and its composition, particularly water content and ion concentration. For example, the cell phone frequency of 915 MHz has a penetration depth of 3.9 cm [199], unable to reach deep brain areas, on the other hand, the MRI frequency of 64 MHz has a penetration depth of 13.5 cm [199], able to get to important deep memory areas of the human brain. Therefore, we should consider the penetration depth of the EMF frequency before we apply it to a human brain because lower radiofrequency (10–200 MHz) have deeper penetration in a human head. Also, we should consider all the tissue layers of the human head that the EMF penetrates because most of the absorbed energy occurs in the superficial tissues. We chose 64 MHz for our studies for several reasons: A) ideal penetration depth (13.5 cm) [199] and homogeneous field distribution, B) previous studies with human cells and mouse cultures did not find toxicity [132], C) it is in the range 30–200 MHz [212] at whole human body resonance, so less power is needed to obtain SAR with a lower TR [213], and D) it has been used by MRI systems for 40 years, thus, providing an established and safe framework for human exposure." {Credits 1}

{Credits 1} 🎪 Perez FP, Walker B, Morisaki J, Kanakri H, Rizkalla M. Neurostimulation devices to treat Alzheimer’s disease. Explor Neurosci. 2025;4:100674. © 2025 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0.