Summary

A bioRxiv preprint reports that 20 MHz focused ultrasound activated auditory circuits and sharply reduced noise-induced hearing loss in anesthetized guinea pigs.

A bioRxiv preprint reports that high-frequency focused ultrasound (FUS) activated auditory pathways and protected guinea pigs from damage caused by loud sound. The researchers targeted the central nucleus of the inferior colliculus (CNIC), an auditory structure in the midbrain, with 20 MHz ultrasound while the animals were anesthetized.

The study found that FUS engaged both incoming auditory pathways and the efferent system, which sends signals from the brain back toward the cochlea. When given before acoustic trauma, the stimulation limited auditory brainstem response threshold shifts to less than 10 decibels, compared with approximately 60 dB in control animals.

Contents

How the study was set up

The researchers applied 20 MHz FUS to the CNIC and recorded electrical responses from the auditory pathway and cochlea. The cochlea is the inner-ear organ that converts sound vibrations into neural signals; the inferior colliculus is a major processing centre for those signals in the midbrain.

The experiment addressed whether FUS could directly activate central auditory neurons in a living animal. The recorded responses suggested a more complex route. FUS produced cortical activity through indirect cochlear activation rather than clear direct activation of the targeted inferior colliculus. The authors suggest that mechanical coupling through the skull may contribute to this effect. Ultrasound-evoked compound action potentials were strongest in the cochlea on the same side as the stimulation.

Auditory circuits responded to stimulation

The stimulation was also associated with c-Fos expression in neurons and glial cells in both the CNIC and auditory cortex. c-Fos is commonly used as a marker of recent cellular activation. These findings led the researchers to conclude that FUS engaged the incoming, or afferent, auditory pathway.

The stronger functional result involved the auditory efferent system. This network carries control signals from the brainstem toward the cochlea and includes medial olivocochlear neurons. FUS reduced compound action potential amplitudes while increasing cochlear microphonics, two electrical measures of cochlear and auditory-nerve activity. The physiological effects lasted for at least two hours, which the authors interpret as evidence of persistent efferent plasticity—the ability of the circuit to change its subsequent response after stimulation.

Protection was measured after noise exposure

The researchers administered FUS before exposing the animals to damaging acoustic stimulation. In the FUS-treated group, the resulting auditory brainstem response threshold shift remained below 10 dB, while control animals showed a shift of about 60 dB. An auditory brainstem response threshold shift represents how much louder a sound must become to produce a measurable response from the auditory pathway; a smaller shift indicates less functional impairment in that test.

The authors describe this as near-complete prevention of noise-induced hearing loss under the study conditions. Gentamicin abolished both the physiological effects of FUS and its protective effect against acoustic injury. That result supports the researchers’ interpretation that activation of medial olivocochlear pathways was central to the protection.

This is an animal study presented as a bioRxiv preprint, rather than a clinical treatment study. The findings identify a possible noninvasive way to engage auditory feedback circuits before noise exposure, but translation to human hearing protection will require further research. The supplied abstract does not report the animal sample size or detailed ultrasound and noise-exposure parameters.

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