A new study using Mongolian gerbils as an animal model demonstrates for the first time that transtympanic infrared laser stimulation of the cochlea elicits reliable auditory-guided behavior in awake animals without the need for genetic modification or invasive surgical implantation. The research was led by Dr. Yuta Tamai, a researcher at Doshisha University’s Acoustic Navigation Research Center (also a Japan Society for the Promotion of Science Research Fellow at Keio University and a researcher at Eberhard Karls University Tübingen), Professor Kohta I. Kobayasi of the University’s Faculty of Biomedical Sciences, and Associate Professor Koji Toda of the Keio University Department of Psychology. The findings were published in an online journal iscience June 30, 2026.
“My research motivation came from observing families with age-related hearing loss who struggled to communicate due to the limitations of traditional hearing aids. Their experience highlighted the need for more effective solutions, as traditional cochlear implants require invasive procedures and have technical shortcomings. It inspired me to investigate non-invasive optical alternatives that provide a natural hearing experience. My goal is to bridge the gap between neuroscience and technology by developing a contactless device that restores the joy of communication to people with hearing loss. Dr. Tamai said while talking about the motivation behind this study.
The researchers used a classical conditioning procedure to make the gerbils learn that the cue and reward, in this experiment, involved water. For one group, the cue was a traditional acoustic stimulus, while for another it was an infrared laser stimulus sent through the eardrum and toward the cochlea.
After training, the laser-stimulated gerbils began licking in anticipation of a water reward, indicating that the laser cue was behaviorally meaningful. Their learning patterns were comparable to those of the sound-trained animals, but the sound-trained animals showed stronger responses overall. This highlighted that transtympanic laser stimulation could serve as a conditioned stimulus to support auditory-guided behavior.
The researchers introduced white noise masking to test whether the laser-induced responses were indeed auditory-related, which reduced responses to normal sounds. Laser-evoked behavioral responses were also significantly reduced, whereas visual cue responses were not significantly affected. This suggests that the laser-induced percepts were processed through the auditory pathway rather than a general sensory disruption.
The study also found that the perception evoked by the laser could be controlled by changing the radiated energy, reflecting how stronger sound pressure levels produce stronger auditory responses. This shows that laser stimulation can modulate the intensity of a percept similar to hearing.
In another test, animals trained with acoustic cues only responded the first time a laser stimulus was presented. This “stimulus generalization” suggests that the laser stimulus produced perceptual features that overlap with the sound. However, the response was weaker than the response to the trained acoustic cue, indicating that the laser-evoked percept is similar to, but not identical to, the click sound.
“In the next five to 10 years, this technology has the potential to revolutionize the treatment of hearing loss. By perfecting optical stimulation across the eardrum, we aim to provide a clinical alternative that minimizes the risks and complications of surgery. It also opens up new avenues for sensory replacement devices, with the potential to improve the quality of life for millions of people who suffer from communication impairments due to hearing loss.” Professor Kobayashi said, emphasizing the practical applications of this technology.
Overall, this study demonstrates that non-contact optical stimulation of the cochlea can be a useful platform to study hearing and indicates that it may be useful for the future development of non- or minimally invasive auditory prosthesis technologies.
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Reference magazines:
Yuya Tamai others. (2026). Optical guidance of auditory perception by cochlear stimulation in non-genetically modified Mongolian gerbils. iScience. DOI: 10.1016/j.isci.2026.116588. https://www.cell.com/iscience/fulltext/S2589-0042(26)01963-2
