The Ever-Changing Brain

By Hannah Glick and Anu Sharma

This article is a part of the September/October 2022, Volume 34, Number 5, Audiology Today issue. 

Hearing loss (HL) is one of the leading chronic health conditions in older adults, with more than 25 percent of adults over the age of 60 years experiencing a clinically significant HL greater than 35 dB HL (World Health Organization, 2022). Age-related HL, or presbycusis, refers to a gradual, progressive, bilateral sensorineural HL and is common among older adults. Because of its insidious nature, age-related HL may not be noticed until communication is significantly affected.

As a profession, we are just beginning to understand the widespread effect of age-related HL on the brain. For example, a brain with untreated age-related HL is associated with greater regional volume loss in the temporal lobe and auditory cortex compared to a brain with hearing within “normal” limits (Lin et al, 2014). As the degree of HL progresses, structural differences become more pronounced (Peelle et al, 2011). Untreated, age-related HL is also associated with dementia (Lin et al, 2011) and communication can become challenging, particularly in noisy environments.

Adults with age-related HL may try to adapt to the HL by focusing more intensely, listening harder, and “filling in the gaps” (Pichora-Fuller et al, 2016). Over time, they may begin to avoid challenging listening environments, potentially contributing to greater rates of social isolation, loneliness, and depression (Glick and Sharma, 2020; Shukla et al, 2020). In this article, we review some of our work exploring the impact of HL on cortical neuroplasticity and cognitive function before and after treatment and the implications of these findings on assessment, treatment, and rehabilitation. 

Using Non-Invasive EEG for Measurement

Sensory neuroplasticity refers to the brain’s ability to modify its structure or function when changes to sensory input occur across the human lifespan. Cortical neuroplasticity refers to the way in which the highest processing center of the brain, the auditory cortex, changes or adapts over the lifespan. Cortical resource allocation refers to the way brain areas participate during a particular task. Cortical cross-modal reorganization refers to situations where deprivation in one sensory modality (e.g., the auditory cortex, as in HL) may lead to brain areas being “repurposed” by other sensory modalities (e.g., vision, touch). 

At the Brain and Behavior Laboratory at the University of Colorado, Boulder, we use a non-invasive, relatively inexpensive neuroimaging method, electroencephalography (EEG), to study cortical neuroplasticity, cortical resource allocation, and cortical cross-modal reorganization in HL across the human lifespan. 

Research indicates that adults with untreated mild to moderate HL show changes in cortical resource allocation during auditory tasks.

Changes in Cortical Resource Allocation

Research from our laboratory indicates that adults with untreated mild to moderate HL show changes in cortical resource allocation during auditory tasks. These changes are correlated with speech-perception abilities in background noise. Specifically, these adults show more diffuse activation across auditory (temporal) cortical regions, as well as regions of the frontal and pre-frontal cortex in response to an auditory stimulus (FIGURE 1B), compared to adults with hearing within “normal” limits who showed activity restricted to auditory (temporal) cortical regions (FIGURE 1A) (Campbell and Sharma, 2013). Further, these changes in cortical resource allocation were associated with lesser speech-in-noise recognition.