Advances in Audiology and Hearing Science

Volume 2: Otoprotection, Regeneration, and Telemedicine

Stavros Hatzopoulos

• Publisher: Apple Academic Press
• Year: 2020
• eBook ISBN: 9781000012460
• Edition: 1
• Topic: Medicina
• Subtopic: Audiologia e logopedia

With chapters from audiology professionals from around the world, Advances in Audiology and Hearing Science presented in two volumes—provides an abundance of information on the latest technological and procedural advances in this ever-improving field.

Volume 1 primarily focuses on revised clinical protocols and provides information on new research to help guide decisions and criteria regarding diagnosis, management, and treatment of hearing-related issues. Topics include new clinical applications such as auditory steady-state response, wideband acoustic immittance, otoacoustic emissions, frequency following response, noise exposure, genomics and hearing loss, and more.

Volume 2: Otoprotection, Regeneration, and Telemedicine includes sections with material related to hearing devices, hearing in special populations, such as the children and the elderly, as well chapters on the fast-growing subfields of otoprotection and regeneration, including pharmacologic otoprotection, stem cells, and nanotechnology.

PART I
Hearing Devices

CHAPTER 1

Assessment of Early Auditory Development in Children After Cochlear Implantation

ARTUR LORENS¹, ANITA OBRYCKA^1*, and HENRYK SKARZYNSKI²

1 Department of Auditory Implant and Perception, World Hearing Center, Institute of Physiology and Pathology of Hearing, Warsaw, Poland

2 World Hearing Center, Institute of Physiology and Pathology of Hearing, Kajetany, Poland

* Corresponding author. E-mail: [email protected]

ABSTRACT

This chapter presents information on cochlear implants (CIs) and their use in the treatment of childhood hearing loss. Specifically, normal auditory development in children is discussed which is critical for clinicians to understand. A rationale is provided for CIs as a means to promote the auditory development of children with profound hearing loss. In addition, the theoretical foundations of methods for assessing auditory development using questionnaires are provided, as well as their clinical application. The role of questionnaires is important to assure valid and effective CI fitting and early intervention programs. Finally, data on CIs suggest that early implantation with young children at 12 months of age is efficacious. Consequently, delaying this process even a short period of time, may lead to unfavorable and unnecessary outcomes.

1.1 INTRODUCTION

Hearing plays an important role in a child’s development. Hair cells in the inner ear transform acoustic energy into neuronal impulses, a transformation which is essential in generating auditory sensation. Damage to these cells can disrupt inner ear function creating sensorineural hearing loss. Depending on the extent and type of damage, an individual’s hearing loss (and therefore impairment) may be more or less severe. In most cases, hair cell damage is irreversible. Consequently, there is no effective medical “cure” for hearing impairment. The only available medical intervention is rehabilitation using a hearing prosthesis such as a hearing aid (HA) or cochlear implant (CI). Hearing aids are typically used in cases of mild to severe hearing loss; cochlear implants are usually reserved for cases of profound hearing loss or total or partial deafness.

1.2 AUDITORY DEVELOPMENT

1.2.1 NEUROPHYSIOLOGICAL FUNDAMENTS OF AUDITORY DEVELOPMENT

To understand auditory rehabilitation with a CI, one needs to appreciate how the auditory system develops and what happens to its neural structures when they are stimulated. A rapid growth in neural structures is first seen at the embryonic stage of development. The process is regulated by the expression of genes, but the final stages of development take place in the period after they have already begun to perform their basic function: the perception of sound (Werner et al., 2012). The synchronous activity of neurons in these structures and in the adjoining afferent system stimulates further development. At the same time, lack of appropriate activity leads to weakening or even loss of synaptic connections. These processes happen simultaneously, with the end result being that the most effective connections are the ones that develop.

The process of intensive reorganization of neural structures during development is called developmental neuroplasticity, and the period of particular susceptibility to change is called the critical period (Cramer et al., 2017). During the critical period, even stimuli acting for only a short period of time may have a significant impact on the final organization of a neural unit. Altered perceptional sensitivities, such as caused by hearing loss, can lead to a permanent impairment of components of the central auditory pathway and how it is organized. Sometimes, however, functional perception can be restored, at least partially, if auditory training is provided (e.g., early intervention programs for children with hearing impairments).

Knowledge of the neuroplasticity of cortical auditory centers has been obtained using electrophysiological studies that concentrate on the latencies of cortical auditory evoked potentials (CAEPs). The latency of the first positive peak (P1) in a CAEP waveform is considered to be a biomarker of the maturity of the auditory cortex (Sharma and Dorman, 2006; Sharma et al., 2007). The latency of P1 is the sum of all the synaptic delays in the peripheral and central segments of the auditory pathway, and since it depends on the age it can, therefore, serve as a measure of auditory pathway maturity (Katz, 1994; Eggermont et al., 1997). Studies of CAEPs conducted on people with normal hearing (NH) permit the range of P1 latencies to be determined for each age group. For example, the P1 latency in a newborn is about 300 ms but, with rapid development, by 2–3 years of age the P1 latency is about 125 ms. By adulthood, the P1 latency has shortened to about 60 ms (Sharma et al., 2002).

1.2.2 A MODEL OF AUDITORY DEVELOPMENT

The Aslin and Smith (1988) general model of perception describes three successive stages of auditory development sensory primitives (Level I), which characterizes basic sensory perception; perceptual representations (Level II), which represents complex coding at higher neural levels; and higher-order representations (Level III), which involves cognitive processing. Carney (1996) has used the Aslin and Smith model to divide auditory perceptual development into three corresponding levels, the level of sound detection resulting in sound awareness (Level I), the level of discrimination that allows sounds to be differentiated (Level II), and the level of identification in which sounds are recognized and interpreted (Level III) (Eisenberg et al., 2007).

1.2.3 AUDITORY DEVELOPMENT IN A TYPICALLY DEVELOPING CHILD WITH NORMAL HEARING

From the moment a child is born, its auditory system is ready to react and process acoustic stimuli (Eisenberg, 1976; Aslin et al., 1983). However, even though the auditory system is capable of performing satisfactorily, it is still refining its capabilities, a process that lasts for the next dozen years or more. As mentioned in the previous section, the three main stages of auditory perception are detection, discrimination, and identification (Carney, 1996; Aslin and Smith, 1988). Each stage of development sees a refinement in these auditory perceptions and their progression can be monitored in children by recognizing certain auditory reactions. At an embryonic age, and in newborns, there are already general and nonspecific reactions to sounds. A sound might cause slight changes in behavior (closing of the eyes, an increase in heart rate). Northern and Downs (1991) have published an overview of the behavioral responses of infants, of which the most important are:

1. Reflexive behaviors: fright, general body movement (large motor), pupil dilation, blinking of eyes, spontaneous face movements, the closing of eyes (auditory reflex, reproducibly evoked from about 24–25 weeks gestational age).
2. Orienting behaviors: turning of the head, widening eyes, raising eyebrows, expressing surprise, sudden cessation of vocalization.
3. Attention behaviors: Stopping an activity, increased ability to act, holding the breath or change of breathing rhythm, sudden crying, sudden stopping of crying or vocalization, widening the eyes, smile or other changes of facial expression.

In the first 2 years of a child’s life, its auditory reactions change. They may react to sounds of progressively less intensity, may show a wider diversity of reactions, or may show more pertinence and repeatability of reactions to specific acoustic stimuli. In the first months of life (up to about 4 months) an infant may take fright (Moro reflex) or awaken in reaction to a sudden, loud sound. Children aged between 4 and 7 months turn their heads toward a sound source outside their field of vision; by 9 months they can localize a sound coming from the side, and by 13 months localize a sound coming from behind. Between 13 and 24 months of life, a child reacts to speech from another room, coming or responding when called (Northern and Downs, 1991).

1.3 COCHLEAR IMPLANTS

Cochlear implants replace the process of transforming sound into neuronal impulses by electrically stimulating the surviving nerve fibers in effect bypassing the defective hair cells (Wilson et al., 1991). Cochlear implant systems consist of an internal and external part. The internal part is the implant, which comprises a receiver and an electrical stimulator in one unit which feeds into a serial electrode array. The external part is a digital multichannel speech processor (Hochmair et al., 2006). Medically, receiving a cochlear implant involves two basic steps. First is the surgical side, where the implant capsu...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• About the Editors
• Contents
• Contributors
• Abbreviations
• Acknowledgments
• Preface
• Part I: Hearing Devices
• Part II: Hearing in the Elderly
• Part III: Otoprotection and Regeneration
• Part IV: Telemedicine
• Answers to End-of-Chapter Questions
• About the Chapter Authors
• Glossary
• Index