Iii Anomia In Alzheimers Disease
Alzheimer's disease (AD) is the most studied of the dementia-producing diseases that can have anomia as a salient symptom. Dementia (see the article on it in this volume) may be defined as a progressive cognitive decline resulting from a number of diseases. Such a cognitive decline characteristically may include more language disturbance (as in Alzheimer's disease in all but very-late-onset instances) or less language disturbance (as in the dementia associated with perhaps one-third of the individuals with Parkinson's disease). When a language disturbance is evident, anomia is invariably a part of it. The naming problems associated with the dementias may or may not be termed anomia by different scholars; however, the phenomenon is quite similar to that found in the aphasias. What underlies the problem, however, appears to be different. First, the cognitive problems underlying the dementia regularly include a variety of memory problems, so one may argue that the difficulty with outputting a name results from the memory problem rather than from a more strictly linguistic problem. At the anatomical level, moreover, the dementias are associated not with sizable, isolatable lesions such as those of the aphasias but rather with multiple lesions at the cellular level, thus suggesting that it is a systemic problem rather than an area contributing to some more or less specific aspect of naming that is impaired when anomia manifests itself.
Linked to the cognitive decline crucial for a diagnosis of dementia is a marked component of semantic impairment evident in the dementias, most particularly in AD. The term "semantic" here is meant to be distinct from the term "phonological" (or "orthographic") in that the borders of meaning of a word seem to become more permeable, or less specific information about the meaning of the word is available. This can be well-demonstrated by a task such as one to probe the semantic attributes of a word. For example, when a patient cannot remember the name penguin, one might ask about superordinate information (e.g., is it a tree? an animal?), coordinate information (e.g., is it a dolphin? a robin?), and subordinate information (e.g., does it eat fish? does it live in a cool climate?). Whereas people with anomia resulting from the aphasias can access all three types of information without difficulty, anomics with AD can, at one point in their cognitive decline, access only the superordinate information and later may even have problems with that. Such semantic problems, however, act in conjunction with more purely lexical-access problems. These may be more severe than those associated with normal age-related problems that the patient would be expected to evidence.
One of the ways one tests for the problem lying at the retrieval stage, as mentioned earlier, is by giving phonemic cues. For patients with AD, these may not be helpful as they are for normal elderly individuals with naming problems. Indeed, patients with AD may appear to "free associate" to the phonological cue: for a picture of a trellis, one says "tre...'' and the patient may respond "trend." Of course such a response does not positively assure that the problem lies at the lexical level; rather, it may be due to inattention to the task. An alternate indication is to look at the consistency with which the patient can name an item over time. If the patient cannot name the trellis one day but can the next, this argues that the item's representation itself is not impaired, but rather retrieval of it is. An additional factor that enters into the naming errors of patients with AD is perceptual difficulty. That is, pictures may draw inappropriate answers ("cucumber" for "escalator") as the patient is drawn to the overall shape or to a subcomponent of the picture.
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