Noise and the Brain

Experience Dependent Developmental and Adult Plasticity

Jos J. Eggermont

• Publisher: Academic Press
• Year: 2013
• Print ISBN:
  9780124159945
• eBook ISBN:
  9780123914316
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

In our industrialized world, we are surrounded by occupational, recreational, and environmental noise. Very loud noise damages the inner-ear receptors and results in hearing loss, subsequent problems with communication in the presence of background noise, and, potentially, social isolation. There is much less public knowledge about the noise exposure that produces only temporary hearing loss but that in the long term results in hearing problems due to the damage of high-threshold auditory nerve fibers. Early exposures of this kind, such as in neonatal intensive care units, manifest themselves at a later age, sometimes as hearing loss but more often as an auditory processing disorder. There is even less awareness about changes in the auditory brain caused by repetitive daily exposure to the same type of low-level occupational or musical sound. This low-level, but continuous, environmental noise exposure is well known to affect speech understanding, produce non-auditory problems ranging from annoyance and depression to hypertension, and to cause cognitive difficulties. Additionally, internal noise, such as tinnitus, has effects on the brain similar to low-level external noise.Noise and the Brain discusses and provides a synthesis of hte underlying brain mechanisms as well as potential ways to prvent or alleviate these aberrant brain changes caused by noise exposure. - Authored by one of the preeminent leaders in the field of hearing research - Emphasizes direct and indirect changes in brain function as a result of noise exposure - Provides a comprehensive and evidence-based approach - Addresses both developmental and adult plasticity - Includes coverage of epidemiology, etiology, and genetics of hearing problems; effects of non-damaging sound on both the developing and adult brain; non-auditory effects of noise; noise and the aging brain; and more

Chapter 1

Introduction

Noise affects the brain in many ways. The most obvious one is by causing hearing loss, which in turn results in changes in the brain that can result in tinnitus. Only in the early 19th century were occupational hazards resulting in deafness identified. Animal studies in the early 20th century discovered the neural substrates thereof, and safe exposure levels were established. More recently, it has been demonstrated that even legally safe noise exposure levels, if presented for a long time, can cause long-lasting changes in the central auditory nervous system, in the absence of demonstrable hearing loss. Recreational noise, such as loud music, currently competes with occupational noise exposure for being a primary cause of hearing impairment. Environmental noise can, beyond being a source of annoyance, also cause sleep problems and stress. This introductory chapter uses a historical approach to this manifold of effects of noise on the brain, and concludes that prevention is the best solution.

Keywords

History; Deafness; Neural substrates; Safe exposure levels; Tonotopic maps; Brain plasticity; Noise annoyance; Noise prevention

Ten thousand years ago, the world must have been a quiet place. But already a few thousand years ago there were busy markets and workplaces of blacksmiths and other artisans. And by that time¹ occupational noise problems such as tinnitus had been noted. In contrast to antiquity, ours is a world of excessive exposure to sound resulting from a variety of occupational, environmental, and recreational sources. The most important aspect in this deterioration of environmental and occupational acoustical conditions is without a doubt the industrial revolution (1750–1850). Environmental sound levels now generally exceed 80 dBA (Figure 1.1).

Figure 1.1 Filter curves (weightings) for sound level measurements (left). The filter gain is plotted as a function of sound frequency on double logarithmic scales. Sound levels with indications of sources and approximate loudness (right). A-weighting (blue) is the most commonly used of a family of curves defined in the International standard IEC 61672:2003 for the measurement of sound levels. The integrated energy below the weighting curve is typically indicated as dBA. A-weighting, which is basically the inverse of the human threshold as a function of frequency, is mandated for the measurement of environmental noise and industrial noise, as well as when assessing potential hearing damage and other noise health effects at all sound levels. For measuring low frequency (infra) sounds the C-weighting (red) is better. The B and D weightings are hardly ever used. Modified from Wikipedia (2011).

According to the World Health Organization’s Guidelines for Community Noise,² noise can result in adverse health effects such as: hearing loss, sleep disturbances, and even cardiovascular problems. In addition, environmental sound may cause behavioral problems such as reduced performance, annoyance reactions, and even adverse social behavior.

Sound may be annoying noise or may be music to our ears; however, for some people music can also be annoying. Recently, more people have become aware of the potential damage that excessive sound (noise as well as music) exposure may cause to our hearing. Whereas there are fairly stringent occupational noise standards to protect workers’ hearing sensitivity, very few people are currently aware of the effects that continuous or interrupted (e.g., day–night) occupational or environmental long-term exposure to non-hearing–loss-causing sound can inflict on the body and brain. In addition to the effects listed in the first paragraph, it is becoming more and more obvious that sounds that do not cover the entire audible frequency range create the most problems.³ These sounds result in long-lasting downregulation of the neural gain in the auditory system over the exposure-sound frequency range combined with an upregulation of the gain in nonexposed frequency regions. This can, for instance, result in differential amplification of vowels and consonants. This is known to be at the source of reduced speech understanding.⁴

Sometimes these frequency-dependent gain-change effects are seen as beneficial. For instance, people who live along a busy street often say that they are no longer aware of the traffic noise. The psychological explanation is that they have habituated to it. Habituation to sound is an example of nonassociative learning that is based on reduced neural activity in the central auditory system and is specific to that particular type of sound. The reduced neural activity in response to such behaviorally meaningless sound may also help in perceiving other meaningful sounds.⁵ Common experience indicates that the city dweller, frequently encountering significant levels of outdoor and indoor noise, becomes accustomed to such exposures and can sleep in their presence. I personally experienced this while staying in Bilbao, Spain, during the festive week of “Asta Nagusta 2012” featuring a drone of loud music and noisy revelers during the entire, and every, night on the square bordering my hotel. The first few nights I hardly could sleep, but the remainder of the week showed great improvement in that respect. However, specifically traffic noise appears hard to habituate to and causes alterations in subjective evaluation of sleep, annoyance, and work performance.⁶ Exposure to environmental sound is one of the many factors that contribute to noise annoyance. Noise annoyance is generally characterized as “a feeling of resentment, displeasure, discomfort, dissatisfaction, or offense when noise interferes with someone’s thoughts, feelings, or actual activities”.⁷ An important question is whether the brain changes that underlie habituation to particular sounds also affect the perception of other sounds. That is not clear and depends on how well habituation as currently defined explains these brain changes. What is known is that long-term exposure to noise (not necessarily damaging) impairs sound processing in auditory cortex as well as attention.⁸

The neuroscience aspects of the problems that I want to address in this book in particular are, first, the effects of traumatic noise leading to hearing loss and the subsequent changes in the auditory brain. Secondly, and perhaps more importantly, I will address our recent discovery that even moderate level sound exposure (long duration continuous or periodic—day/night) also has long-lasting effects on the adult brain without causing audiometric hearing loss. This happens even more so in neonates, infants and children, and thus is a life-span problem. The ultimate effects of such exposures may be similar in all age groups, but they are induced faster and leave permanent changes in a neonatal and infant brain. In contrast, these changes are induced slower and are up to a point spontaneously but slowly reversible in adult brains. The sounds that induce these changes are generally behaviorally irrelevant—i.e., do not require any behavioral actions. Sound without behavioral meaning is colloquially described as noise. In real life this can be occupational, recreational, environmental or, if loud enough, so-called traumatic noise. Loud noise above the occupational-noise exposure limits can damage the cochlea, causes hearing loss, and as a consequence also induces changes in the brain. Long-term exposure to moderate-level noise can also result in dramatic frequency-dependent changes in cortical neural sensitivity without causing hearing sensitivity loss. Besides these neuronal changes in the auditory brain, noise exposure can also cause sleep disturbances resulting in stress, hypertension and potentially cardiovascular problems, and thus in the long term affects both brain and nonbrain systems. The sound-to-brain interface that causes these bodily changes is becoming better defined. We will explore these findings in Chapters 10 and 11. Still, sound is required for normal auditory brain development.⁹ Powerful electric prostheses (cochlear implants) can restore sound perception to such an extent that normal conversation is possible. We will explore the effects thereof on the brain in Chapter 5.

1.1 Discovery of Noise as a Cause of Hearing Loss

In addition to being a statesman, Sir Francis Bacon (1561–1626) wrote essays on hearing speech and sound. These are included in his book Sylva Sylvaram: Or a naturall historie in ten centuries.¹⁰ He describes therein his experience with a temporary hearing threshold shift and transient tinnitus:

“A very great sound, neere hand, hath strucken many Deafe; And at the Instant they have found, as it were, the breaking of a Skin or Parchment in their Eare: And my selfe standing neere on that Lured loud, and shrill, had suddenly an Offence, as if somewhat had broken, or beene dislocated in my Eare; And immediately after, a loud Ringing; (Not an ordinary Singing, or Hissing, but farre louder, and differing;) so as I feared some Deafenesse. But after some halfe Quarter of an Houre it vanished.”

Two hundred years later, Fosbroke¹¹ provided a quite comprehensive account of the etiology of hearing loss. He distinguished between traumatic deafness following the sudden explosion of a cannon, and deafness caused by occupational noise, e.g., blacksmith’s deafness. He reported two cases of traumatic deafness, “that of Lord Rodney after the eighty broadsides fired from his ship the Formidable, in 1782”, and a second from the report of “a cannon close to the individual at the battle of Copenhagen.” He then describes the deafness suffered by blacksmiths as being (cited in¹²):

“… a consequence of their employment; it creeps on them gradually, in general at about forty or fifty years of age. At first the patient is insensible of weak impressions of sound; the deafness increases with a ringing and noise in the ears, slight vertigo, and pain in the cranial bones, periodical or otherwise, and often violent. No wax is formed. It has been imputed to a paralytic state of the nerve, occasioned by the noise of forging, by certain modem writers, and by the old writers, to permanent over-tension of the membrane, which they compare to fixed dilatation of the pupil.”

Systematic studies in occupational deafness were also emerging in the late 1800s. The studies by Gottstein and Kayser in Germany, and by Barr in Scotland, were identified by Atherley and Noble¹² as the two principal landmarks representing research in this time period. I follow their extensive review. Gottstein and Kayser¹³ were the first to perform a controlled study by comparing the hearing of an experimental group, comprising blacksmiths and metal workers, with that of a control group consisting of bricklayers. They assigned “good,” “fairly bad” and “bad” hearing to those who could hear whispered speech beyond 3 m, those who could hear it only at a distance of 2–3 m, and those who could hear it only when presented close to the ear or not at all. Note that whispered speech contains mostly high frequencies, and that this test does not assess residual low-frequency hearing. They found increasing hearing loss with age in the blacksmiths: none over the age of 50 could hear well and those that were older presented nearly total loss of hearing. By contrast, only two of the 36 bricklayers were in the “fairly bad” or “bad” categories.

Barr’s¹⁴ main testing equipment was his pocket watch. He reported this “being heard when the hearing is normal 36 inches from the ear.” How the distance for normal hearing was arrived at Barr does not say, but it was likely determined by holding his watch at arms-length; 36 inches equals one yard. Barr used his watch to test the hearing of 100 men working as boilermakers in two Glasgow shipyards. He characterized them as follows:

“The 100 men examined represent all ages, from 17 years, the youngest, to 67, the oldest. The average age was 35. The most serious results were found, as might have been expected, in the older men. The average number of years during which they had been exposed to the sounds of boi...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Abbreviations
• Chapter 1. Introduction
• Chapter 2. Epidemiology, Etiology and Genetics of Hearing Problems
• Chapter 3. Neural Substrates of Noise-Induced Hearing Loss
• Chapter 4. Effects of Nondamaging Sound on the Developing Brain
• Chapter 5. Effects of Deafness on the Young Brain
• Chapter 6. Speech Understanding in Noise
• Chapter 7. Effects of “Nondamaging Sound” on the Adult Auditory Brain
• Chapter 8. Noise and the Aging Brain
• Chapter 9. Music and the Brain
• Chapter 10. Nonauditory Effects of Noise
• Chapter 11. Noise in the Brain
• Chapter 12. Protection Against Noise-Induced Brain Changes: Are there Safe Noise Levels?
• Index