Functional magnetic resonance imaging (fMRI) is a non-invasive technique that
allows for visualization of active brain regions. Although white matter (WM) constitutes
approximately 50% of brain tissue, fMRI activation in WM has conventionally been
dismissed. There are two main reasons WM fMRI remains controversial: 1) the blood
oxygen level dependent (BOLD) fMRI signal depends on cerebral blood flow and
volume, which are lower in WM than gray matter and 2) fMRI signal has been associated
with post-synaptic potentials as opposed to action potentials. Despite these observations,
there is no direct evidence against measuring fMRI activation in WM.
This thesis is comprised of four manuscripts that investigate fMRI activation in
WM at 4T. The first study evaluated whether it was possible to detect WM activation
using an interhemispheric transfer task and examined whether certain MRI contrast
mechanisms were more sensitive to activation in WM. Activation was detected in the
anterior corpus callosum at the individual and group level and we discovered that T2
weighted imaging may provide increased sensitivity to activation in WM. The second
study used two established interhemispheric transfer tasks to examine whether callosal
activation could be experimentally manipulated using a within subjects design. The
results replicated previous findings and demonstrated an ability to map functional
activation in the corpus callosum that was task dependent. The third study examined WM
fMRI activation in a different structure and focused on the posterior limb of the internal
capsule using a motor task; activation was elicited at both individual and group levels.
The fourth study linked advances in the ability to detect WM fMRI activation to current
clinical approaches to the assessment of WM dysfunction. An adapted Symbol Digit
Modalities Test was used to evaluate WM activation in healthy controls. The results
revealed individual level activation in both the corpus callosum and internal capsule.
Taken together this stream of research represents a major advance in the methods
used to non-invasively study brain function. Future applications may include improved
assessment methods for patients with WM dysfunction.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:NSHD.ca#10222/15093 |
| Date | 17 July 2012 |
| Creators | Gawryluk, Jodie Reanna |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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