A thesis submitted in partial fulfilment of - Queen Margaret University

larger intracranial capacity could withstand more brain ageing (or injury) before
cognitive impairment becomes detectible than smaller intracranial capacity
(Kesler et al., 2003). Active processes considered to be factors involved in
accumulating cerebral reserve include the intellectual challenges experienced
throughout our lifetime, such as intelligence, education and occupational levels
(Staff et al., 2004; Whalley et al., 2004; Kesler et al., 2003; Plassman, Welsh,
Helms, Brandt, Page, Breitner, 1995).
Some studies have attempted to evaluate the impact of ageing on cognitive
decline. One such study in Scotland replicated the Scottish Mental Survey of
1932 (school children aged 11) with 235 of the same participants (aged 77 at
follow-up) comparing the findings to the data of 1932 and also provided MRI
data for 98 of these participants (Staff et al., 2004). Unlike Kesler et al. (2003)
cerebral size was not supported as a passive factor in cognitive reserve. It was
reported that childhood intelligence contributed to non-verbal reasoning abilities
at age 77 years and both education and a cognitively complex occupation
predicted higher cognitive ability in old age. Additionally, relationships were
found between memory and education, memory and occupation, as well as
reasoning and occupation. An interesting trend in this replicated study indicated
a substantial stability in the rank-ordering of human intelligence across the life
span where children who scored highly in assessments at age 11 tended to
score highly at age 77 and vice versa. A cross-sequential study in Seattle also
recorded the intellectual and cognitive capacity of a population from childhood to
adulthood (over 5000 participants) (Schaie, 1994). This study reported a decline
of intellect with ageing in areas of inductive reasoning, spatial orientation,
perceptual speed and verbal memory, however, there was much less age
related decline in verbal and numerical ability.
It is however difficult to establish baseline measures of active factors such as
pre-morbid intelligence and cognitive status, to enable comparison with a
36