December 6 2023 marked the launch of an exciting new Oticon initiative, the BrainHearing™ Network, aimed at connecting scientists and hearing care professionals worldwide.

In the first webinar of this series, we had the pleasure of hosting Prof. Anu Sharma from the University of Colorado (Boulder) to discuss the consequences of hearing loss on the brain. As Prof. Sharma stated: “There is this clear ear-brain connection that suggests that hearing loss not only impacts the ear but also the central auditory pathways.” Her talk focused on the central consequences of hearing loss, highlighting neuroplasticity in age-related hearing loss after briefly touching on its effects in children.

Neuroplasticity in Children with Hearing Loss

So, what is neuroplasticity? Prof. Sharma explained: “A basic tenet of neuroplasticity is that the brain will change or reorganize following sensory deprivation.” To study this phenomenon in children, she uses the P1 auditory cortical evoked response—a biomarker of neuroplasticity originating from the primary auditory cortex. This biomarker helps assess auditory cortex maturation as children grow.

Children with cochlear implants (CIs) show more typical auditory cortex development when implanted early (ideally by 9-12 months; Sharma et al., 2007). However, later implantation often results in incomplete cortical development, impacting oral language acquisition despite normal audiogram performance. This effect stems from a partial decoupling between the primary auditory cortex and higher-order cortical functions, which can also affect executive function, attention, working memory, and motor planning. In short, hearing loss has cascading effects beyond the audiogram.

Can this knowledge support clinical decision-making? Studies by Sharma and Dorman (2006), Sharma et al. (2007, 2015) observed P1 response changes after hearing aid (HA) fitting or CI implantation, assessing whether auditory stimulation was sufficient to restore normal cortical maturation. Today, Prof. Sharma applies P1 response testing in clinical practice to assess children with hearing loss, auditory neuropathy spectrum disorder (ANSD), and multiple disabilities. She concludes that cortical potentials provide valuable insights into auditory cortex maturation, helping determine whether a child benefits from HAs or requires a CI.

Cross-Modal Plasticity

Beyond auditory system effects, Prof. Sharma discussed cross-modal compensatory plasticity, where other sensory systems compensate for auditory deprivation. Research by Campbell and Sharma (2016) demonstrated this phenomenon: children with CIs recruited auditory brain areas in response to visual stimuli, unlike normal-hearing children who activated only the visual system.

Clinically, this compensation correlates with speech perception ability—struggling CI users showed stronger cross-modal plasticity. Further studies (Sharma et al., 2015) found that cross-modal plasticity levels distinguish good from average CI users, even when their audiograms appear similar.

Interestingly, this effect is not exclusive to profound congenital deafness; it also occurs in mild-to-moderate hearing loss (Campbell & Sharma, 2014). In other words, even mild hearing loss can reorganize the brain. Traditional audiograms might suggest no need for intervention, but these findings highlight the importance of looking beyond the audiogram.

Additionally, hearing loss engages frontal and prefrontal brain regions, indicating that listening becomes effortful even in mild cases. As Prof. Sharma emphasized: “If you are pulling in cognitive resources just to listen, how much cognitive reserve do you have left?” Supporting this, Glick and Sharma (2020) found that untreated mild-to-moderate hearing loss correlated with poorer cognitive function across multiple measures.

Reversal of Cross-Modal Plasticity After HA Fitting

These findings raised an important question: Can amplification through HA fitting reverse these brain changes? Glick and Sharma (2020) demonstrated that six months of HA use reversed cross-modal reorganization, significantly improving both cognitive function and speech-in-noise perception. This suggests that cross-modal plasticity is reversible if addressed early.

Prof. Sharma concluded: “If you provide early and appropriate treatment, restoring auditory cortex gain, you likely reverse cross-modal plasticity, decrease cognitive compensation, reduce listening effort, and restore balance between the senses.” However, she stressed that appropriate fitting is key—HAs must be properly adjusted to restore auditory cortex gain. Currently, she is investigating brain reorganization differences between users of over-the-counter hearing aids and professionally fitted devices.

Key Takeaways

• The audiogram does not fully describe the consequences of hearing loss.
• Even mild-to-moderate hearing loss can trigger cross-modal plasticity, increased cognitive effort, and poorer cognitive test performance.
• Early and appropriate HA fitting may reverse cross-modal reorganization, reducing cognitive strain and restoring natural brain function.

For more information on Dr. Sharma’s research, visit: https://www.colorado.edu/eeglab

Want to Learn More About Oticon’s Beyond the Audiogram Approach?

A New Standard of Speech-in-Noise Prescription with Audible Contrast Threshold (ACT™)

Address the #1 complaint of people with hearing loss—difficulty understanding speech in noise. ACT quickly provides language-independent insights into a user’s hearing-in-noise ability and prescribes the appropriate level of help.

With an average test time of just two minutes, ACT enhances the fitting process, optimizing hearing experiences for clients. Test results seamlessly integrate into Oticon Genie 2 for fast and personalized hearing-aid fitting.

Learn more about ACT

Unlock Your Clients’ BrainHearing™ Potential

With your client’s ACT value, you can prescribe the right level of hearing-aid assistance from the start, optimizing sound to support the brain’s natural way of processing auditory information.

Read more about the benefits of BrainHearing

References

Sharma, A. & Dorman, M.F. (2006). Central auditory development in children with cochlear implants: Clinical implications. Adv Otorhinolaryngol, 64, 66-88.

Sharma, A., Gilley, P. M., Dorman, M. F., & Baldwin, R. (2007). Deprivation-induced cortical reorganization in children with cochlear implants. International Journal of Audiology, 46(9), 494-499.

Campbell, J., & Sharma, A. (2014). Cross-modal reorganization in adults with early-stage hearing loss. PLOS One, 9(2), e90594.

Sharma, A., Campbell, J., & Cardon, G. (2015). Developmental and cross-modal plasticity in deafness: Evidence from P1 and N1 event-related potentials in cochlear-implanted children. International Journal of Psychophysiology, 95(2), 135-144.

Glick, H. A., & Sharma, A. (2020). Cortical neuroplasticity and cognitive function in early-stage, mild-to-moderate hearing loss: Evidence of neurocognitive benefit from hearing aid use. Frontiers in Neuroscience, 93.