Language Disorders

As people age, they tend to experience changes in language functioning. Some aspects, like the use or understanding of complex syntax, typically show signs of decline. Others, like vocabulary knowledge, improve with age, though the older one gets the more difficult it becomes to retrieve from the lexicon the precise words one wants. While full-blown language disorders are not the norm for elderly people, some particular language disorders are more likely to co-occur with advancing age, because the medical conditions that cause them primarily affect older individuals. These conditions include stroke and dementing illnesses. Their common language after effects include aphasia, right hemisphere communication disorders, and the language of generalized intellectual impairment.

Aphasia is an acquired language disorder. Typically, it is the result of damage to the left side of the brain, which for most individuals is "dominant" for language functions. The damage that induces aphasia is usually cortical and peri-Sylvian, which means that it affects the outermost layers of brain cells that surround the Sylvian fissure (see Figure 1). Most often caused by stroke, aphasia also can result from other conditions, like head trauma, when the brain damage predominantly affects left peri-Sylvian regions.

Aphasia affects both the expression and interpretation of language, through all of its channels, Figure 1 Left hemisphere of the brain showing the Sylvian Fissure and the approximate location of Broca's and Wernicke's areas of the angular gyrus. SOURCE: Adapted from Hart, S. and Semple, J. S. Neuropsychology and the Dementias. London: Taylor and Francis (1990): 166. but to different degrees in different individuals depending on the nature and extent of brain damage. Language changes that reflect sensory deficits, such as hearing loss, do not constitute aphasia. Also, language impairment in aphasia is disproportionate to, and cannot be explained by, other types of cognitive changes, such as memory problems.

A word retrieval deficit, or difficulty in selecting the precise words one wants to use from an unaltered lexical store, is a universal symptom of aphasia. These word retrieval difficulties, often called anomia, are more frequent and less likely to be resolved than the word retrieval challenges of normal aging. It is important to note, though, that word retrieval deficits are common after any kind of brain damage; thus, they are not diagnostic. The other language systems are variably affected in adults with aphasia.

Classical views of aphasia divide it into syndromes or types, such as Broca's and Wernicke's aphasia. Each type has some expressive and receptive characteristics that grossly differentiate it from other types of aphasia, and that are presumed to stem from damage to particular peri-Sylvian regions in the left cerebral hemisphere. However, it has become clear that damage confined to a particular brain area (e.g., Broca's or Wernicke's area; see Figure 1) does not generate a lasting aphasia of the same type. More generally, the accuracy and value of aphasia syndrome classifications, as well as the correspondence between language disorder profiles and brain lesion locations, are the subject of much debate (see, e.g., commentaries following an article by Yosef Grodzinsky). Research is ongoing to specify the complex relationships among normal brain anatomy and its contribution to the functioning of various language systems, as well as the precise ways in which particular kinds of brain damage produce particular types of language symptoms.

Right hemisphere language disorders also can result from stroke. This time the stroke affects the side of the brain that is not dominant for language; typically, as the name implies, the right hemisphere. These disorders have been systematically studied since the mid-1980s. Because so little is known about the nature of right hemisphere language deficits, there is not yet an appropriate diagnostic label. However, some descriptive generalizations are possible. Strokes that are restricted to the right hemisphere in older adults appear to have little effect on phonology, morphology, or syntax, and their consequences for lexical-semantic processing are unclear. But adults with right hemisphere damage can be particularly impaired in pragmatic aspects of language. As senders, for example, they may have special difficulty supplying content that is appropriate to the communicative circumstances, by assuming that a receiver knows something that he or she does not know, or by being too wordy, too terse, too detailed, too tangential, and/or too vague. As receivers, they may be particularly impaired at understanding implications that are not directly stated, such as those conveyed by nonliteral language (e.g., jokes or irony) or other ambiguous information. These difficulties, while not always immediately obvious to others, can render adults with right hemisphere damage quite socially disadvantaged.

Finally, the language of generalized intellectual impairment (Wertz) is a diagnostic label that refers to language disorders resulting from neurologically degenerative processes such as Alzheimer's disease. In people with the language of generalized intellectual impairment, both sides of the brain typically are affected by the degenerative process. Thus, these individuals may have a constellation of language deficits that includes any or all that typify aphasia and right hemisphere language disorders. In addition, however, they generally have other cognitive deficits, such as difficulties with memory and attention, that cause, contribute to, or confound their language symptoms.

Many clinicians, including most medical professionals, use the term aphasia to refer to language disorders that accompany neurologically degenerative conditions. However, many clinical aphasiologists, like Robert T. Wertz, find value in distinguishing the two labels, in part because prognoses and treatment options differ substantially. People who have strokes improve, sometimes dramatically. This occurs naturally as the brain heals, as well as through language therapy. In addition, as alluded to earlier, the nature of the language impairments typically is different in adults who have simple strokes versus dementias. The language deficits in adults with dementing conditions may be rooted in, or are at least significantly complicated by, profound cognitive impairments, such as difficulties in learning and remembering new material. To illustrate, immediately after they hear a brief prose passage, adults with incipient dementia can retell it normally; but after only fifteen minutes, they may recall nothing about it. This is not the case for adults with the other language disorders reviewed above. For them, the difference between immediate story retelling and short-term recall is much less extreme, and may be on par with that for normally aging adults (e.g., Bayles and Kaszniak).