Noninvasive Optical Stimulation Induces Auditory Perception

A team from Doshisha University (Japan), working with collaborators at Keio University, reports that trans-tympanic infrared laser stimulation can drive reliable, auditory-guided behavior in awake Mongolian gerbils—without genetic modification and without invasive cochlear implantation. The results, published online in iScience on June 30, 2026, suggest a contactless route to generate “sound-like” percepts from the cochlea.

In classical conditioning experiments, gerbils learned that a predictive cue preceded a water reward. One group received a conventional sound cue, while another group received infrared laser energy delivered through the eardrum and aimed at the cochlea. After training, animals began licking in anticipation when the laser cue was presented, indicating the stimulation carried behavioral value comparable to an auditory signal.

Learning dynamics showed that laser-evoked conditioning supported anticipatory responses with a similar overall pattern to sound-based training, though sound produced stronger effects. To test whether the response was truly auditory-related rather than a general distraction, the researchers introduced white-noise masking during laser-associated tests.

When masking was applied, responses tied to ordinary sound were reduced, confirming the masking manipulation worked. Importantly, masking also significantly weakened laser-evoked behavioral responses, while visual cue responses remained largely unchanged. This pattern supports the interpretation that the laser-induced percept is processed through auditory pathways.

The study also examined dose dependence by varying radiant energy. Stronger laser output produced stronger behavioral responses, paralleling how higher sound pressure levels yield more robust auditory perception. This tight mapping between stimulus intensity and percept strength strengthens the case for laser stimulation acting as a controlled sensory input.

Finally, animals trained only with acoustic cues responded when laser stimulation was introduced, demonstrating stimulus generalization. The response was weaker than that elicited by the trained sound, suggesting the laser condition activates perceptual features overlapping with a clicking-like stimulus, but not identical to the original auditory cue.

Overall, the work provides an experimentally validated foundation for contactless optical cochlear stimulation as a platform for studying auditory perception and as a potential stepping-stone toward less invasive auditory prosthetic technologies.