DEMENTIA
Progressive cognitive dysfunction due to deterioration of brain tissue. A major problem lies in determining whether the resulting language impairment is linguistic (reflecting damage to the stored systems of grammar and lexis) or cognitive (reflecting damage to areas such as memory, attention and problem-solving which facilitate the use of the grammar and the lexicon).
A second problem lies in distinguishing the effects of dementia from the normal effects of ageing. Some commentators suggest that dementia represents a heightening of the impact of ageing, seen, for example, in difficulties in retrieving words. However, an elderly speaker can often locate a ‘lost’ word if given a cue to its initial sound, whereas dementia sufferers cannot. Dementia sufferers frequently resort to coining a new word when a known one cannot be retrieved.
The way in which dementia impacts upon language depends greatly upon the area of the brain which is affected. Some forms of dementia such as Alzheimer’s disease affect the cortex while others (including many cases of Parkinson’s disease) affect the subcortical areas.
Subcortical dementia leads to a general slowing of activity, which may result in problems of articulation. Speech tends to be affected more noticeably than the language system as a whole, though the ability to retrieve words may be impaired. Similarly, writing may be affected at the level of execution: typical symptoms are small letters and irregular spacing between words. Subcortical dementia is sometimes interpreted in terms of damage to the capacity to control and focus attention: hence problems with manipulating information such as the attachment of inflections in writing.
When cortical dementia begins relatively young, there is a higher probability of extensive language impairment than when the onset occurs at a more advanced age. Some of the effects resemble those of aphasia, especially Wernicke’s aphasia; this is unsurprising, given that the syndrome affects similar areas of the brain.
Sufferers from cortical dementia retain some of the more highly automatised linguistic skills until quite late in the condition. Their phonology is spared, and they usually remain capable of reading aloud. Their utterances show some degree of syntactic structure, including correct word order; and they may be able to correct grammatical errors. Well-established formulaic utterances are especially well preserved, though they may not be used appropriately.
However, their conversation is marked by a lack of cohesion and multiple changes of topic. Lexical retrieval is severely affected: whereas aphasics can often provide clues to a word which they cannot locate (e.g. initial letter, number of syllables), cortical dementia sufferers cannot. Despite this, the semantic relations which support spreading activation (the links between DOCTOR and nurse, patient, hospital) appear to be relatively robust. This suggests that the semantic system is at least partly intact; and that the speaker’s difficulties lie in accessing it.
There has been interest in the way in which dementia affects bilinguals. The language acquired first is more likely to be spared than one acquired later. There is also evidence that some bilinguals become less adept at switching between their languages, and use the wrong one in certain circumstances.
See also: Ageing
Further reading: Hamilton (1994); Maxim and Bryan (1994); Obler and Gjerlow (1999: Chap. 8)
