The specific features of many sounds that we hear and the significance attached to these sounds are unique for each individual and cannot be anticipated by a genetic code. To meet the challenge of uniqueness, the brain contains mechanisms for neural plasticity that tune auditory neurons to represent the sounds that are meaningful to us. We use brain imaging and acoustic training methods to understand how neural plasticity modifies sensory maps in children and adults and to uncover the principles and mechanisms involved.
The knowledge gained from laboratory studies is applied to understand how plasticity sculpts foundations for auditory skills in professional musicians and in children receiving music training and how it may generate tinnitus (chronic ringing of the ears), an auditory deafferentation syndrome affecting quality of life for millions of individuals world-wide.
Some recent highlights from the lab are listed below (click on the links to learn more). The tabs at the top of the home page provide more information about the laboratory (people, publications, research, and a link to send an email message). Inquiries are welcome.
RECENT LAB HIGHLIGHTS (Updated Feb 2018)
PhD candidate Calvin Staples (a registered MSc audiologist) has joined the laboratory and is conducting research on hearing aids as strategy to reduce tinnitus (chronic ringing of the ears). The study will measure the sound frequencies contained in the patient's tinnitus using computerized tools developed in the laboratory. The measurements are then used to adapt the amplification profile of the hearing aid for optimal tinnitus suppression. The effectiveness of the procedure is being compared to conventional hearing aid fitting in a 3-month cross-over design. His next topic for study will assessing hearing loss that may be hidden from the clinical audiogram in tinnitus sufferers using psychoacoustic and EEG methods.
Brandon Paul completed his PhD defense and has published a study on hidden hearing loss in tinnitus sufferers who have normal audiograms. His results (obtained by combining behavioral and electrophysiological measures of neural coding with cochlear modeling) suggested that damage to auditory nerve fibers with high rates of spontaneous firing in quiet is especially important in tinnitus. The activity of these fibers in quiet may preserve the balance of excitation and inhibition in auditory pathways. Brandon was co-supervised by Larry Roberts and Ian Bruce. You can find his study by clicking this link.
Study of bimodal auditory/somatosensory treatment of tinnitus published
Dr. Susan Shore and her team at the University of Michigan used bimodal auditory-somatosensory stimulation to desynchronize brain circuitry and reduce tinnitus in animals and humans. We collaborated with the Shore team on the human study. The results can be seen by clicking this link.
Neural Plasticity and its Initiating Conditions in Tinnitus
Larry Roberts was asked by the HNO Journal to discuss how deafferentation of auditory pathways leads to tinnitus-generating hypersynchronous neural activity in central auditory structures. His article is based on presentation to the Berlin Tinnitus Symposium in December 2016. The article can be found by clicking this link.
Tinnitus and Reduced Sound Level Tolerance in Adolescents
A research team in Sao Paulo Brazil with which we collaborate found that 28.8% of 170 adolescents enrolled in a private school experienced a persistent verified tinnitus and reduced sound level tolerance (hyperacusis) during psychoacoustic assessment in a sound booth, even though their hearing thresholds (to 16 kHz) and otoacoustic emissions were normal. Risky listening habits were near universal among the teenagers. We suggest that tinnitus and reduced SLT are early indications of a vulnerability to possible hidden synaptic injury that is prevalent among adolescents and expressed following exposure to high level environmental sounds. The study by Sanchez, Moraes, Casseb, Cota, Freire & Roberts (2016) may be found in Scientific Reports (Nature Publishing Group). Click here for a reprint.
Maladaptive Plasticity in Tinnitus
Forward Masking Reveals Different Roles for Primary and Nonprimary Cortex in Tinnitus
Tinnitus can be briefly suppressed following exposure to masking sounds that cover the tinnitus frequency region (TFR). This is called “residual inhibition” in the tinnitus literature. We report evidence that suppression of spontaneous and hypersynchronous activity in the TFR by forward masking generates RI and delivers an accompanying off-frequency masking effect, putatively owing to a release of lateral inhibition outside of the tinnitus region. These effects are expressed in brain responses that localize to sources in primary auditory cortex while responses generated in nonprimary regions show very different properties. A model for tinnitus, RI, and off-frequency masking effects is presented that aligns with human and animal data (Roberts, Bosnyak, Bruce, Gander, and Paul, Hearing Research, 2015). Click here to see a reprint.
Eggermont and Roberts (2015) review converging evidence from animal models and studies of human tinnitus sufferers which indicates that most cases of tinnitus are not generated by irritative processes persisting in the cochlea but by changes that take place in central auditory pathways when auditory neurons lose their input from the ear. Forms of neural plasticity underlie these neural changes, which include increased spontaneous activity and neural gain in deafferented central auditory structures, increased synchronous activity in these structures, alterations in the tonotopic organization of auditory cortex, and changes in network behavior in nonauditory brain regions detected by functional imaging of individuals with tinnitus and corroborated by animal investigations. Research on the molecular mechanisms that underlie neural changes in tinnitus is in its infancy and represents a frontier for investigation.
Review and model for role of attention in tinnitus
Roberts, Husain, and Eggermont have reviewed behavioral and functional brain imaging evidence for persisting auditory attention in tinnitus and presented a qualitative model for how attention operates in normal hearing and may be triggered in tinnitus accompanied by hearing loss. The model proposes that the disparity between the predicted and delivered auditory inputs activates a system for auditory attention that facilitates through subcortical neuromodulatory systems neuroplastic changes that contribute to the generation of tinnitus.
Study of neural plasticity in tinnitus highlighted by the Tinnitus Research Initiative
Our study of how the expression of neural plasticity in central auditory structures is modified in tinnitus compared to hearing-level match controls was highlighted in the September 2012 newsletter of the Tinnitus Research Initiative. We observed changes in primary (but not secondary) auditory cortex that were consistent with neural dynamics in the auditory core region that are believed to contribute to tinnitus. To view a pdf of the article, click here.
E-Book on the Neuroscience of Tinnitus published
Eggermont and Roberts edited a series of studies on “Ringing Ears: The Neuroscience of Tinnitus” recently published as an electronic book by Frontiers in Systems Neuroscience. For further information click here.
Brandon Paul joins the Laboratory
We welcome PhD student Brandon Paul to our laboratory. Brandon completed his MSc in Speech and Communication Sciences at Ohio State University earlier this year. He is planning a series of studies on the role of attention in tinnitus. A related interest is in cochlear factors that discriminate between individuals with hearing loss and tinnitus from individuals with hearing loss alone.
MIMM’s LIVE Laboratory Completed