Showing papers by "Brenna C. McDonald published in 2006"

Mechanisms of working memory dysfunction after mild and moderate TBI: evidence from functional MRI and neurogenetics.

Abstract: Cognitive complaints are a frequent source of distress and disability after mild and moderate traumatic brain injury (TBI). While there are deficits in several cognitive domains, many aspects of these complaints and deficits suggest that problems in working memory (WM) play an important role. Functional imaging studies in healthy individuals have outlined the neural substrate of WM and have shown that regions important in WM circuitry overlap with regions commonly vulnerable to damage in TBI. Use of functional MRI (fMRI) in individuals with mild and moderate TBI suggests that they can have problems in the activation and allocation of WM, and several lines of evidence suggest that subtle alterations in central catecholaminergic sensitivity may underlie these problems. We review the evidence from fMRI and neurogenetic studies that support the role of catecholaminergic dysregulation in the etiology of WM complaints and deficits after mild and moderate TBI.

Regional brain atrophy in cognitively intact adults with a single APOE ε4 allele

Abstract: Objective: To determine whether cognitively intact adults with the APOE e3/e4 genotype show reduced gray matter density on voxel-based morphometry (VBM) vs those homozygous for the e3 allele. Methods: Participants were healthy, cognitively intact, right-handed adults, age 19 to 80, who completed genotyping, neuropsychological testing, and MRI. Forty-nine participants had the e3/e3 genotype and 27 had the e3/e4 genotype. Gray matter data were analyzed using the general linear model as implemented in the Statistical Parametric Mapping package, adjusting for age and sex. Results: The e3/e4 participants showed lower gray matter density than the e3/e3 participants in right medial temporal and bilateral frontotemporal regions as well as other areas. There were no regions in which e3/e4 participants showed higher gray matter density than e3/e3 participants. Conclusions: Regionally reduced gray matter density is detectable in cognitively intact adults with a single copy of the APOE e4 allele.

Functional magnetic resonance imaging of the primary somatosensory cortex in piglets.

Abstract: Object The piglet is an excellent model for the developing human brain, and has been used increasingly in various centers for studies of traumatic brain injury and other insults. Unlike rodent or primate models, however, there are few behavioral scales for the piglet, and the available ones are used to test general responsiveness rather than specific functional outcome. The differing behavioral repertoires of animals of different ages provide an additional challenge when age-dependent injury responses are compared. To overcome these experimental limitations of piglets in brain injury research, the authors developed a functional magnetic resonance (fMR) imaging paradigm that can be used to track recovery in the somatosensory cortex over time in anesthetized animals of different ages. Methods Fifteen fMR imaging studies in eight piglets were performed before and after scaled cortical impact injury to the primary somatosensory cortex subserving snout sensation. Specific anesthetic and imaging protocols enabled visualization of cortical activation, and comparison with somatosensory evoked potentials obtained before and after injury was obtained. A piglet brain template for group-level analysis of these data was constructed, similar to the fMR imaging techniques used in humans, to allow for group comparisons and longitudinal change analysis over time. Conclusions Loss of function in a specifically traumatized cortical region and its subsequent recovery over time can now be demonstrated visually by fMR imaging in the piglet. Besides its value in understanding intrinsic recovery mechanisms and plasticity at different ages, this functional outcome measure will enable the use of the piglet model in treatment trials specifically designed for the immature brain.