Electromagnetic stimulation of the auditory system: effects and side-effects

Area of Science:

• Neuroscience
• Audiology
• Biomedical Engineering

Background:

• Extracranial electromagnetic stimulation (EMS) is a non-invasive technique for activating nervous systems.
• EMS is utilized in neurology and otolaryngology for brain and facial nerve stimulation.
• The auditory system's response and potential risks of EMS require investigation.

Purpose of the Study:

• To evaluate the efficacy of EMS in eliciting auditory sensations in profoundly hearing-impaired individuals.
• To assess the safety and side effects of EMS on the auditory system in humans and animals.
• To characterize the acoustic artifact generated by EMS and its potential for causing hearing damage.

Main Methods:

• Non-invasive EMS was applied to 18 deaf or severely hard-of-hearing patients using a magnetic coil at various cranial positions.
• Auditory sensations were recorded, and thresholds of auditory sensation (TAS) were determined.
• Acoustic measurements of the magnetic coil acoustic artifact (MCAA) were performed in animal models and human cranial models.

Main Results:

• EMS successfully elicited auditory sensations in 14 out of 18 patients across different coil placements.
• Thresholds of auditory sensation (TAS) ranged from 20-50% of the maximum EMS level (2.0 Tesla).
• The MCAA generated by EMS reached levels up to 160 dB SPL, with significant energy in the 2-5 kHz range, posing a risk for hearing loss.

Conclusions:

• EMS can stimulate residual auditory pathways and evoke sensations in deaf individuals.
• The high-intensity acoustic artifact produced by EMS is a significant side effect, capable of causing permanent sensorineural hearing loss.
• Further research is needed to mitigate the risks associated with the MCAA during EMS application.