Introduction

The neurobiological changes that a person undergoes with advancing age produce structural and functional changes in all of the organs and organ systems in the body. The upper respiratory system, the larynx, vocal tract, and oral cavity all reflect both normal and abnormal changes that result from aging. In 1983, Ramig and Ringel suggested that age-related changes of the voice must be viewed as part of the normal process of physiological aging of the entire body (Ramig and Ringel, 1983). Neurological, musculoskeletal, and circulatory remodeling account for changes in laryngeal function and vocal output in older adults. These changes, however, do not necessarily result in abnormal voice quality. A thorough laryngological examination coupled with a complete voice assessment will likely reveal obvious voice disorders associated with aging. It still remains for the clinicians along with the help of the patient to identify and distinguish normal age-related voice changes from voice disorders. This entry describes neurological aging-related voice disorders and their treatment options. Traumatic or idiopathic vocal fold paralysis is described in another entry, as is Parkinson's disease. This article focuses on neurologically based voice disorders associated with general aging.

Voice production in the elderly is associated with other bodily changes that occur with advancing age (Chodzko-Zajko and Ringel, 1987), although changes in specific organs may derive from various causes and mechanisms. The effects of normal aging are somewhat similar across organ systems. Aging of the vocal organs, like other organ systems, is associated with decreased strength, accuracy, endurance, speed, coordination, organ system interaction (i.e., larynx and respiratory systems), nerve conduction velocity, circulatory function, and chemical degradation at synaptic junctions.

Anatomical (Hirano, Kurita, and Yukizane, 1989; Kahane, 1987) and histological studies (Luchsinger and Arnold, 1965) clearly demonstrate that differences in structure and function do exist as a result of aging. The vocal fold epithelium, the layers of the lamina propria, and the muscles of the larynx change with aging. The vocal folds lose collaginous fibers, leading to increased stiffness.

The neurological impact to the aging larynx includes central and peripheral motor nervous system changes. Central nervous system changes include nerve cell losses in the cortex of the frontal, parietal, and temporal lobes of the brain. This results in the slowing of motor movements (Scheibel and Scheibel, 1975). Nerve conduction velocity also contributes to speed of voluntary movements such as pitch changes, increased loudness, and speed of articulation (Leonard et al., 1997). Nervous system changes are also associated with tremor, a condition seen more in the elderly than in young individuals. Finally, dopaminergic changes which decline with aging may also affect the speed of motor processing (Morgan and Finch, 1988).

The peripheral changes that occur in the elderly are thought to be broadly related to environmental effects of trauma (Woo et al., 1992), selective denervation of type II fast twitch muscle fibers (Lexell, 1997) and decrease in distal and motor neurons, resulting in decreased contractile strength and an increase in muscle fatigue (Doherty and Brown, 1993).