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David M Yousem

Publications and source records attributed to David M Yousem.

40 records · Page 3Linked to original sources
PubMedDate not supplied

Association, commissural, and projection pathways and their functional deficit reported in literature.

This study demonstrates normal white matter structures of the supratentorial system revealed by diffusion tensor imaging. Their anatomic connections and functional significance are discussed in the context of the lesion-induced deficits reported in the literature, which may not fully represent the lesion-induced effects on the white matter function and may not be entirely specific to the tract discussed. Nevertheless, understanding the most common effects of lesions on the functional connectivity provides a framework that we can use in advanced neuroimaging studies, like diffusion tensor imaging, functional magnetic resonance imaging, and positron emission tomography, and in our daily clinical practice.

Brain↗
PubMedDate not supplied

Timing of cortical activation: a latency-resolved event-related functional MR imaging study.

BACKGROUND AND PURPOSE: The time course of cortical activations of different anatomic areas has been demonstrated to reflect, to some degree, the temporal dynamics of the brain network. The purpose of this study was to determine the temporal sequence of the hemodynamic response in the visual, supplemental motor (SMA), and primary motor cortical areas by using a visuomotor reaction time task. METHODS: The reaction times (RTs) of 26 right-handed subjects were recorded in response to a visual cue during an event-related functional MR imaging (fMRI) experiment. Statistical parametric mapping (SPM99) was used, and activation maps were produced for each subject. This was followed by a random-effects group analysis. Using a weighted least-squares approach, we recorded the time at onset of the hemodynamic response of the fMRI activation in four regions of interest: the right occipital (RO) and left occipital (LO) visual cortices, the SMA, and the left sensorimotor area (LM1). Linear regression analysis was done between the RTs and the mean latencies for the four areas. RESULTS: Using the group analysis, the results showed that the first regions to activate were the visual occipital cortices (RO and LO) with mean latency +/- standard error of mean (SEM) of 1.74 +/- 0.05 s and 1.85 +/- 0.08 s, respectively. The visual occipital areas were followed by the SMA of 2.07 +/- 0.16 s and finally the LM1 with a mean latency of 2.1 +/- 0.15 s. There were significant differences in the mean onset of latencies between RO and LO, RO and SMA, and RO and LM1 (P <.05). On performing regression analysis between the RTs and the mean latencies by using the group analysis, there was no significant correlation with any of the four areas. By using an individual subject analysis, the results again showed that the first regions to activate were the visual occipital cortices (RO and LO) with mean latency +/- SEM of 1.75 +/- 0.06 s and 1.84 +/- 0.12 s, respectively, followed by the SMA with a mean latency of 2.19 +/- 0.25 s and finally the LM1 of 2.26 +/- 0.38 s. There was no significant difference between the mean onset latencies. CONCLUSION: The onset of the hemodynamic response started first in the visual cortex (input) followed by the SMA and primary motor cortical area (output). The onset of activation showed no direct correlation with the overall RTs of the subjects, leading one to suggest that the peripheral motor unit may have a greater impact on RT than the central contribution.

Adult↗
PubMedDate not supplied

Middle cerebral artery infarction: relationship of cavernous carotid artery calcification.

BACKGROUND AND PURPOSE: This study was designed to determine whether calcification of the cavernous carotid artery (CCA) is associated with cerebrovascular infarcts in the same way that coronary artery calcification scores indicate myocardial infarctions. We sought to correlate the grade of CCA calcification with infarctions in the middle cerebral artery (MCA) distribution. METHODS: Nonenhanced brain CT scans of 40 patients with MCA-distribution strokes, 34 with non-MCA-distribution strokes, and 94 age-matched control subjects were reviewed. Circumferential calcification and thickness of calcification were graded for the CCAs on head CT scans. Scores were determined for the left and right CCAs. Mann-Whitney tests and Spearman correlation coefficients were used to detect differences between patients and control subjects and between patients with MCA and those with non-MCA strokes. RESULTS: CCA calcification scores did not significantly differ in the groups compared. The manner in which calcification was scored (by using circumference, thickness, or both) did not affect the results. No difference was noted between scores ipsilateral and those contralateral to the stroke. CONCLUSION: Circumferential degree or thickness of cavernous artery calcification was not correlated with MCA or non-MCA infarctions. CCA calcification scores did not differ between patients with stroke and those without stroke.

Adult↗