In science, there has been an uptick in the use of electrical stimulation to "biohack" our bodies and brains, whether it is to wake us up or for physical therapies. As a result, many new studies have emerged to understand the body's natural stimulation and create tech that mimics it to address a variety of issues. Currently, scientists are digging deeper to determine which frequencies are the best for humans to create devices specifically for nerve degeneration.
During our class, we heard from Dr. Vincent Chen, whose focus was Power Spectral Density (PSD). PSD describes the power of a time-domain signal, or how a random process can be distributed across different frequencies. Chen's hypothesis is as follows: we should manipulate the waveform shape to target NMDA and AMPA receptors, which act as switches that turn on nerve growth. His clinical success with "random noise" stimulation is due to the rich PSD. He also questions modern electrical stimulation methods, as square waves commonly used contain harmonics, echoes of higher frequencies hidden within the signal. With these higher frequencies, it makes it harder to determine which signal is most optimal for nerve regeneration actively. Just following the frequency to him is imprecise because the signal will degrade as soon as it passes through the skin and tissue. He notes that the nerve membrane acts as a capacitor, resisting sudden changes, so changing the type of wave could also affect the nerve differently. By controlling the voltage gradient, he can target very specific receptors. Chen's approach is highly specific, and with the future of implantable devices, it blows all past nerve studies out of the water.
A different study conducted by Dr. Lingmei Ni uses very traditional electrical stimulation approaches to alleviate the effects of nerve damage. Ni uses multiple types of electrical stimulation, including NMES (neuromuscular), and low-frequency pulses to contract the muscles, helping prevent muscle atrophy directly. TENS is transcutaneous, blocking the pain signals with varying high and low frequencies. FES is the functional frequency, which can help paralyzed limbs return to function. These therapies have been used for a long time, but Ni has clinical data on specific frequencies to support her statement. Her studies show that 1 hour of 20Hz stimulation is proficient to accelerate axon growth after carpal tunnel surgery. Electrical stimulation increases BDNF and cAMP, which act as fuel for a growing neuron. However, even Dr. Ni points out how there is no standard for electrical stimulation. It varies between patients, parts of the body, and at times can seem almost random.
These studies, when read together, can be seen as the future of electrical stimulation. Dr. Ni has a wide breadth of knowledge and clinical data on electrical stimulation, helping regenerate axons faster. Dr. Chen takes it one step further; no longer will the frequency or even type of wave vary from person to person. Rather, using PSD data, we can build stimulators that do not cause nerve fatigue or unwanted pain from high-frequency harmonies. With this amalgamation of information, other scientists can take this data to build more biohacking devices to help humans live more comfortable lives following nerve degeneration.
Chen, VincentC.-F., et al. "Accelerating Peripheral Nerve Regeneration Using Electrical Stimulation of Selected Power Spectral Densities." Neural Regeneration Research, vol. 17, no. 4, 2022, p. 781, https://doi.org/10.4103/1673-5374.322458.
Ni, Lingmei, et al. "Electrical Stimulation Therapy for Peripheral Nerve Injury." National Center for Biotechnology Information, U.S. National Library of Medicine, 23 Feb. 2023, pmc.ncbi.nlm.nih.gov/.
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