Celebrating Better Hearing and Speech Month with BPS Member Research

2013_BHSM_logo_175(1)May is Better Hearing and Speech Month, so we sat down to learn about some of the latest research from BPS member Suhrud Rajguru, University of Miami. More information about the awareness month is available from the American Speech-Language-Hearing Association.

What research projects are you currently working on?
In individuals with severe-to-profound hearing loss, cochlear implants (CIs) stimulate the remaining functional cochlear nerve fibers by applying electrical current directly into the cochlea. CIs encode acoustical information derived from high-frequency sounds into electrical pulse trains that are delivered in the base and low-frequency signals in the apex of the cochlea and have been successfully implanted in more than 220,000 people. Contemporary implants use up to 22 intracochlear electrode contacts delivering electrical pulses to the cochlear nerve. Although users can discriminate stimuli on multiple electrodes, clinical and psychophysical studies have shown that implant users do not achieve functional performance on all channels due to spread of electric current in the tissue.

My current work focuses on developing a novel optical technique, infrared neural stimulation (INS) using pulsed infrared radiation (λ=1860nm), for potential applications in CIs for treatment of hearing loss. Optical stimulation can provide significant improvements in spatial selectivity and potentially increase the number of independent channels in future cochlear implants. By discrete stimulation of a particular location along the length of the cochlea, the devices will attempt to mimic the natural sound encoding in the auditory pathway.

I am also interested in studying the biophysical mechanism(s) of infrared stimulation of excitable cells and applying the stimulation for applications in basic science and therapeutics. In collaboration with Dr. Richard Rabbitt at the University of Utah, we have found that pulsed infrared stimulation resulted in contractions of cardiomyocytes and excited neurons and sensory hair cells of the auditory and vestibular systems. At the University of Miami, my research group has found that infrared evokes strong intracellular Ca2+ responses in stem cell derived cardiomyocytes as well as cochlear spiral ganglion and vestibular ganglion neurons. Ca2+ imaging in combination with a wide array of pharmacological agents shows that pulsed IR evoked mitochondrial Ca2+ cycling plays a key role in the cells response to infrared light. I am currently working on applications of this innovative stimulus to study synaptic transmission in the auditory and vestibular systems.

How do those projects relate to hearing and/or speech?
Optical techniques have several advantages over conventional electrical stimulation. Optical radiation does not spread significantly in the tissue when compared with electric current. The infrared stimulus provides a non-contact, artifact free method that acts through endogenous mechanisms to stimulate neurons. With INS we may be able to achieve two to three times the number of independent stimulation sites. The ability to localize the stimulation and simultaneously and independently target different cochlear regions can lead to improvements in user listening performance in noisy environments and may result in better music appreciation by providing more independent channels to encode the acoustic information.

When you started these projects, were you specifically trying to address a hearing and/or speech problem? If not, how did your research lead to these issues?
My doctoral work with Dr. Rabbitt involved biomechanical modeling of the vestibular system to study Benign Paroxysmal Positional Vertigo (BPPV), the most common vestibular disorder leading to vertigo. During this time I became very interested in treatments of balance disorders and hearing loss. I was fortunate to be able to team with Dr. Claus-Peter Richter at Northwestern University for my postdoctoral work and study infrared neural stimulation as a novel technology for cochlear implants.

What practical applications could your projects have?
This innovative infrared stimulus can lead to novel experiments in cell biophysics, including applications at subcellular levels. It provides an alternative tool to excite and pace cells and can be advantageous over conventional electrical or chemical stimuli. The ability to control spatial extent of excitation by focusing the optical stimulus can be especially beneficial in therapeutic applications, including treatment of hearing loss, tinnitus, imbalance and deep brain stimulation.

What do you hope to accomplish in the future with this research?
I will continue my research to elucidate the mechanism(s) of infrared stimulation and expand its application. Understanding the mechanism will lead to novel optical and genetic approaches in the study of auditory and vestibular neuroscience (and beyond) and open up new frontiers in neuroprosthetic applications.


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