Cognitive deficits are highly prevalent in multiple sclerosis (MS) and have a negative
impact on daily life. Impairments in information processing speed are among the most
commonly reported deficits in MS and are generally assessed by evaluating mean-level
performance on time-limited tests. However, this approach to assessing performance
ignores potential within-subject differences that may be useful for characterizing
cognitive difficulties in MS. An alternative method of measuring performance on timed
cognitive tasks is to examine the degree of within-subject variability, termed intraindividual
variability (IIV). IIV provides information about the characteristics of an
individual’s performance and may provide novel information about cognitive functioning
in MS and other neurodegenerative disorders. The research presented in this dissertation
examined IIV in performance as an indicator of cognitive functioning in persons with MS
and explored the relations of performance variability to measures of neuronal
connectivity derived from resting state functional magnetic resonance imaging (rsfMRI).
Individuals with MS were found to be both slower and more variable on tests of
information processing speed and attention. This variability was observed even when
controlling for sensorimotor confounds and other systematic variables that may influence
variability, such as practice and learning effects. IIV in performance was found to better
distinguish MS patients from matched groups of healthy control subjects when compared
to common clinical measures of cognitive performance or average response speed. These
differences in IIV were also found consistently across six monthly assessments in a group
with MS who remained clinically stable over this period. This stability in IIV suggests its
feasibility as a measure of changes in longitudinal cognitive or clinical status. Using
rsfMRI, greater stability in performance (i.e., lower IIV) was associated with greater
functional connectivity between frontal lobe regions (i.e., ventral medial prefrontal cortex
and frontal pole) in persons with MS. This increased connectivity appears to represent
potential compensatory processes within mildly affected MS individuals. Together the
findings demonstrate that IIV is an important characteristic of cognitive performance that
may provide new insights into the cognitive deficits present in MS.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/35408 |
| Date | 24 July 2013 |
| Creators | Wojtowicz, Magdalena |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
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