Noise-induced hearing loss (NIHL) is one of the most common types of hearing loss
among adults. The World Health Organization estimates that 10% of the world's population
is exposed to sound levels that could potentially cause NIHL (Chadha et al., 2021).
This Research Topic focused on NIHL was opened for submission from September 2021
to July 2022, with one opinion, four reviews, and eight original articles being included.
Exposure to industrial noise is one of the most common risks for NIHL. With the development
of industrialization, non-Gaussian noise (also known as complex noise), which transients
high-energy impulsive noise superimposed on the steady-state background noise, has
been the primary noise type in the industry. Recent evidence showed that the temporal
structure of complex noise could be expressed in the kurtosis metric (β), which is
defined as the ratio of the fourth-order central moment to the squared second-order
central moment of a distribution (Zhang et al., 2022a). Zhou et al. investigated the
epidemiological characteristics of occupational NIHL among 1,050 manufacturing workers
in China and found that kurtosis strengthens the association between noise exposure
duration and noise intensity with high-frequency hearing loss. Shi et al. further
validated the application of cumulative noise exposure (CNE) adjusted by kurtosis
when evaluating occupational NIHL associated with non-Gaussian noise among 1,558 manufacturing
workers from five industries in China. Their serial of studies demonstrated that the
kurtosis-adjusted-CNE metric is more effective than CNE alone in assessing occupational
NIHL among workers under non-Gaussian noise exposure. Recently, a draft guideline
for measuring workplace noise exposure based on their work has been proposed in China
(Zhang et al., 2022b).
NIHL is a complex condition with indiscernible mechanisms that result from exposure
to loud sounds, and as research illustrates, is likely influenced by age, sex, genetics,
underlying diseases, personal behaviors, and other physical and chemical hazards (Basner
et al., 2014; Wang et al., 2021a). Chen et al. summarized primarily human studies
as well as animal studies concerning the role of susceptible genes in NIHL, aims to
provide insights into the further exploration of NIHL prevention and specific treatment.
Meanwhile, Kurabi and team theorized several possible molecular pathways might be
involved in NIHL (Kurabi et al., 2017). Zhao et al. focused on the adenylate-activated
kinase (AMPK) pathway, and found that early AMPK activation may protect hearing by
increasing ATP storage and reducing the release of large quantities of p-AMPK, which
could help to inhibit synaptic damage.
Despite numerous investigations into NIHL, treatment options are still limited and
preventive measures are not well implemented. NIHL can be avoided if appropriate preventive
measures are adopted (The, 2019). Bramati et al. provided insights into the Dangerous
Decibels® program for the prevention of NIHL for noise-exposed workers. Their study
showed greater effectiveness than the conventional educational-based intervention
in a Brazilian population. In addition to occupational noise exposures, other noises
may stem from everyday occurrences, and there are growing concerns about the increasing
incidence of NIHL in children and adolescents who are potentially exposed to an array
of loud sounds on a daily basis (Dillard et al., 2022). However, for non-occupational
noise exposure, it is challenging to regulate as it would have to accommodate for
the wide range of possible high-intensity sound sources, as there is high variability
in activities that involve loud sounds for young people in their daily life. With
the increasing application and contributions of neuroscience in recent NIHL studies,
Pang and Gilliver proposed an opinion that neuroscience-informed approaches to reducing
recreational NIHL for young people are required to meet the needs of the developing
adolescent brain. Designing age-appropriate NIHL campaigns that consider these factors
may increase the likelihood that interventions are efficacious and cost-effective.
Of late, several studies indicated that even moderate noise exposure could result
in hearing difficulties in individuals with normal hearing thresholds, which has been
referred to as “hidden hearing loss (HHL)” (Kohrman et al., 2020). Despite progress
in pre-clinical models, evidence supporting the existence of HHL in humans remains
inconclusive, and clinicians lack any non-invasive biomarkers that are sensitive to
HHL (Bramhall et al., 2019; Wang et al., 2021b). Here, Valderrama et al. reviewed
animal models of HHL as well as the ongoing research that aims to develop tools with
which to diagnose and manage hearing difficulties associated with HHL. They discussed
new research opportunities facilitated by recent methodological tools that may overcome
a series of barriers that have hampered meaningful progress in diagnosing and treating
of HHL.
Noise-induced synaptopathy (NIS) has been researched extensively as a potential cause
of coding-in-noise deficits (CIND) and HHL. However, by using low-level, intermittent
noise exposure mimicking the human experience in guinea pigs, Xia et al. found that
degradations in signal processing were likely limited and not reflective of NIS and
noise-induced HHL. Similarly, Pinsonnault-Skvarenina et al. also failed to find any
significant association between noise exposure and auditory brainstem response outcomes,
which might have detected cochlear synaptopathy in young factory workers with normal
hearing. Ripley et al. further summarized the translational difficulties from animal
data to human clinical, the technical challenges in quantifying NIS in humans, and
the problems with the spontaneous rates theory on signal coding. The temporal fluctuation
profile model was discussed as a potential alternative for signal coding at a high
sound level against background noise, in association with the mechanisms of efferent
control on the cochlea gain.
Cumulative damage from long-term noise exposure is also a major cause of age-related
hearing loss, tinnitus, and even degraded learning and cognitive abilities (Manukyan,
2022). For noise-induced tinnitus, Hayes et al. developed the appetitive operant conditioning
paradigm to assess acute and chronic sound-induced tinnitus in rats, which provides
a platform for future investigations into the neural basis of tinnitus. For cognitive
dysfunction related to noise exposure, Patel et al., exposed 6-month-old rats to an
occupational-like noise and studied both hippocampal-dependent and striatal-dependent
cognitive dysfunction. They highlighted that even mild noise exposure early in adulthood
could have long-lasting implications for cognitive function later in life. Manohar
et al. reviewed recent results that illustrate how NIHL deprives higher-order structures
than the cochlea (such as the hippocampus) of the vital sensory information needed
to carry out complex, higher-order functions.
We hope that this collection of articles on NIHL has provided readers with a comprehensive
understanding of the current state of research in this area. Through the exploration
of various influencing factors, mechanisms, prevention strategies, and non-auditory
effects of NIHL, we have gained valuable insights into the complexities of this condition.
As we move forward, we encourage readers to use this information to guide their own
research and clinical practices. Whether through the development of new prevention
strategies or the advancement of early diagnosis and precise therapy, there is much
work to be done in the NIHL area.
One key message that unites this entire collection is the importance of collaboration
and interdisciplinary approaches to NIHL research. Only through the joint efforts
of clinicians, scientists, engineers, and other stakeholders can we hope to make meaningful
progress in our understanding and management of this population. We urge readers to
join this effort and work toward a future where NIHL is a preventable and treatable
condition.
Author contributions
All authors except QW were guest editors of the Research Topic. QW was the research
assistant and secretary on the Research Topic. All authors wrote the paper and approved
the submitted version.