A series of studies is presented investigating characteristics of
the cognitive impairments found in Dementia of the Alzheimer Type
(DAT), Multi-Infarct Dementia (MID), and other neurological and
psychiatric conditions causing cognitive impairment.
ychiatric conditions causing cognitive impairment.
Introductory material includes suitable definitions of the
diagnostic conditions, descriptions of the nature of DAT and MID, and
discussion of issues concerning whether important differences exist
within the DAT category depending on the age at which the condition
The main initial study is a cross-sectional study of patterns of
cognitive impairment, as assessed by a battery of neuropsychological
tests, in groups of DAT and MID subjects of different ages and in a
group of subjects with other conditions resulting in cognitive
impairment. 58 DAT, 58 MID, and 58 other subjects are fully assessed;
additional subjects receive only a short form of the test battery.
Differences in patterns of cognitive impairment between diagnostic
groups and between different age groups within diagnostic groups are
described; the possible significance of these findings is discussed
with reference to any possible artefacts arising from methodology or
subject selection procedures.
A follow-up study of samples of these groups involves a second
neuropsychological assessment 10 months after the first. Patterns of
decline in different groups are described, and efforts are made to
identify predictors of the extent of decline over 10 months based on
subjects' test performances or personal characteristics at initial
assessment. The extent of decline shows considerable variation even
within diagnostic groups, and is only rather weakly predictable using
the information gathered at initial assessment.
The remainder of the thesis comprises a number of relevant smaller
studies. The first is an investigation of relationships between
neuropsychological test performance and everyday functioning as
assessed by a behaviour rating scale in ninety of the subjects
initially tested as described above. The significance of the
relationships found is discussed with reference to clinical
psychological practice. The second is a study of short-term day to day
variability in cognitive functioning in small groups of DAT and MID
subjects involving three administrations of a brief test battery
within a two-week period. Little variability is found in either group,
and the notion that MED subjects characteristically fluctuate more
from day to day than DAT subjects do is not supported. The rest of the
studies involve detailed analyses of certain particular aspects of
cognitive functioning in DAT, MID, and other cognitively impaired
subjects. Same draw on data collected in the main initial study
described above (previous presentation of such detailed analyses
having been inappropriate when considering overall patterns of
performance); others are separate experiments, with smaller numbers of
subjects. The data presented principally concern aspects of memory,
language function, and psychomotor performance. A variety of findings
from these detailed analyses are noted and their importance discussed.
Finally the findings of all the studies are reviewed and some
tentative conclusions drawn.