Oyster toadfish (Opsanus tau) are commonly used in research on vestibular physiology, the study of balance. Recent research has examined hair cells from the toadfish's crista ampullaris, a structure in the inner ear that senses and responds to movement of the head. The hair cells convert mechanical vibrations produced by sound, gravity or motion into signals that are transmitted to the brain by adjacent nerve cells.

Credit: Mark Strozier

The new research showed that hair cells could be stimulated by pulses of infrared radiation to send signals to the brain. This type of optical, rather than electrical, stimulation had been previously shown to activate nerve and heart cells in various animal models. In a press release, Richard Rabbitt (University of Utah, Salt Lake City), who led the research, summarized, “[We] talk to the brain with optical infrared pulses instead of electrical pulses.” The results have potential therapeutic applications for hearing loss and for certain balance and movement disorders (such as Parkinson's disease) in humans.

The toadfish study was published in the Journal of Physiology (589, 1283–1294; 2011) alongside a companion paper reporting on the mechanism of the cellular response to infrared radiation (J. Physiol. 589, 1295–1306; 2011). The latter study used neonatal rat cardiomyocytes. Taken together, the two reports suggest that infrared radiation stimulates hair or heart cells by triggering uptake and subsequent slow release of intracellular calcium ions ([Ca2]) by mitochondria. This [Ca2] cycle is a normal cellular process, but “it's normally controlled by the cell, not by us,” said Rabbitt in a press release, continuing, “the infrared radiation gives us a tool to control the cell.”

These results may someday lead to the development of improved cochlear implants to treat deafness. Currently available cochlear implants convert sound into electrical signals that are typically transmitted to a number of electrodes (8–24). The number of electrodes is limited, and these implants provide a limited range of hearing. Optical stimulation, instead of electric, may enable a wider range of sound sensitivity, more realistically representing natural hearing. Such implants would probably not be available for at least 5–10 years, according to Rabbitt.

Similarly, optical stimulation may also enable the development of devices to preserve vision in certain types of vision loss and to maintain balance and restore movement in disorders like Parkinson's disease.