Structural changes in the frontal and temporal lobes and in subcortical white
matter tracts often occur following closed head injury (CHI). In contrast to this well
delineated structural pathology, the post-traumatic cognitively-related functional
changes in these and other brain regions have not been adequately described.
To characterize the long-term functional neuroanatomy of CHI, the present
study compared regional cerebral blood flow (rCBF) patterns in 13 severely-injured,
well-recovered, unmedicated patients to those from 13 well-matched healthy controls.
rCBF was measured using oxygen-15 water intravenous bolus positron emission
tomography (PET) while subjects performed the Wisconsin Card Sorting Test
(WCST), an indicator of prefrontal lobe functioning that involves matching stimuli to
a changing sorting principle based on external feedback, and a Cued Recall Memory
Test (CRMT), which involves remembering semantically-related word pairs. The
neuropsychological tasks were used to provoke specific neural systems believed to be
important in task performance (the prefrontal cortex in the former, the hippocampus in
the latter). Subjects also performed two specially designed sensorimotor control tasks
to provide measures of baseline rCBF.
Given the controversy regarding the statistical analysis of PET data, a two-pronged
method was utilized: 1) Statistical Parametric Mapping, the state-of-the-art
technique that examines rCBF throughout the entire brain, and 2) region of interest
analysis, an anatomically-based method for examining rCBF in a limited set of brain
regions. Between-group rCBF differences were tested in the four tasks separately and
also in the two neuropsychological tasks after subtracting baseline rCBF (i.e., rCBF
activation). To characterize the relationship between cerebral perfusion and behavior,
correlations were performed between performance and rCBF activation (i.e., task-control)
for each group separately, and between rCBF activation and an index of
current neuropsychological functioning for the CHI patients.
Analyses of each task separately revealed that, compared to controls, CHI
patients showed lower rCBF in anterior cingulate cortex (ACC) and subcortical areas.
Analyses of rCBF activation data revealed: 1) increases in left inferior frontal gyrus
(including Broca's area) and left hippocampus of CHI patients relative to control
subjects during the WCST, 2) a negative correlation between task performance and the
right hippocampus during the WCST in CHI patients, and 3) correlations between the
hippocampus and performance during the CRMT in the CHI patients that were in the
opposite direction to those found in the control subjects.
These neurofunctional changes are compatible with the structural and cognitive
sequelae of CHI First, given a hypothesized role of the ACC in attentional processes,
reduced rCBF in this region of CHI patients may relate to the persistent and often
subtle difficulties in attention after CHI, whereas rCBF diminutions in subcortical
regions may relate to diffuse damage to or deafferentation of subcortical regions in
this CHI sample. Second, given similar (although slightly, but not significantly,
poorer) performance on the WCST by the CHI patients, increased left prefrontal
cortical activity may partially reflect behavioral compensation (e.g., subvocalization to
aid memory during the task) and also physiological compensation for inefficiencies in
other brain areas (e.g., subcortical regions). Finally, in light of the relatively poorer
task performance of CHI patients (non-significant tendency in the WCST but highly
significant in the CRMT), differences between the groups in the direction of the
correlations between performance/cognition and hippocampal activation may suggest
disorganization of hippocampal functioning in CHI patients.
This exploratory and descriptive investigation identifies brain structures with
post-traumatic changes that may be important to cognition. These results may provide
evidence of both behavioral and neurophysiological compensation in patients with
severe CHI. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/9764 |
| Date | 23 July 2018 |
| Creators | Kirkby, Brenda Sue |
| Contributors | Graves, Roger Elliott, Berman, Karen F. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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