Diffusion tensor imaging has been used extensively as a research tool to understand the structural changes associated with white matter pathology. Using water diffusion as the basis to construct anatomic details, diffusion tensor imaging offers the potential to identify structural and functional adaptations before gross anatomical changes, such as lesions and tumors, become apparent on conventional MRI. Over the past 10 years, further parameters, such as axial and radial diffusivity, have been developed to characterize white matter changes specific to axons and myelin. In this paper, the potential application and outstanding issues on the use of diffusion tensor imaging directional diffusivity as a biomarker in axonal and myelin damage in neurological disorders will be reviewed. Keywordsacute and chronic CNS disorders; acute disseminated encephalomyelitis; Alzheimer's disease; axial diffusivity; axonal injury; diffusion tensor imaging; leukodystrophy; MRI; multiple sclerosis; myelin damage; radial diffusivity Principles of diffusion tensor imagingDiffusion tensor imaging (DTI) is a noninvasive, quantitative MRI technique that measures the rate and direction of movement of water molecules within tissues. In the CNS, axonal
Objective: We measured the long-term retention of knowledge gained through selected American Academy of Neurology annual meeting courses and compared the effects of repeated quizzing (known as test-enhanced learning) and repeated studying on that retention.Methods: Participants were recruited from 4 annual meeting courses. All participants took a pretest. This randomized, controlled trial utilized a within-subjects design in which each participant experienced 3 different postcourse activities with each activity performed on different material. Each key information point from the course was randomized in a counterbalanced fashion among participants to one of the 3 activities: repeated short-answer quizzing, repeated studying, and no further exposure to the materials. A final test covering all information points from the course was taken 5.5 months after the course.Results: Thirty-five participants across the 4 courses completed the study. Average score on the pretest was 36%. Performance on the final test showed that repeated quizzing led to significantly greater long-term retention relative to both repeated studying (55% vs 46%; t[34] 5 3.28, SEM 5 0.03, p 5 0.01, d 5 0.49) and no further exposure (55% vs 44%; t[34] 5 3.16, SEM 5 0.03, p 5 0.01, d 5 0.58). Relative to the pretest baseline, repeated quizzing helped participants to retain almost twice as much of the knowledge acquired from the course compared to repeated studying or no further exposure.Conclusions: Whereas annual meeting continuing medical education (CME) courses lead to longterm gains in knowledge, when repeated quizzing is added, retention is significantly increased. CME planners may consider adding repeated quizzing to increase the impact of their courses. Continuing medical education (CME) comprises a major component of both maintenance of certification and maintenance of licensure in most states.1,2 The rationale behind this position is that life-long learning is a critical part of professional development.2 The American Academy of Neurology (AAN) is a major source of CME for neurologists in the United States. Each year, thousands of neurologists spend considerable time and money to attend the annual meeting of the AAN in order to meet their CME requirements and to learn about the latest advances in the field. In order to better meet the educational needs of practicing neurologists, the AAN has developed interactive education sessions such as NeuroFlash and Morning Report sessions. 3NeuroFlash sessions use audience response systems to engage learners in presentations about recent developments in a topic. Morning Reports use a case-based discussion format to explore challenging clinical scenarios. These new formats focus not only on facts but on the clinical application of those facts, which is a key part of the definition of competence used for accreditation of CME courses. 4,5 Although increasing interaction during these sessions is a good educational strategy, a single, brief exposure to information may not be enough to produce
The discordance between genome size and the complexity of eukaryotes can partly be attributed to differences in repeat density. The Muller F element (∼5.2 Mb) is the smallest chromosome in Drosophila melanogaster, but it is substantially larger (>18.7 Mb) in D. ananassae. To identify the major contributors to the expansion of the F element and to assess their impact, we improved the genome sequence and annotated the genes in a 1.4-Mb region of the D. ananassae F element, and a 1.7-Mb region from the D element for comparison. We find that transposons (particularly LTR and LINE retrotransposons) are major contributors to this expansion (78.6%), while Wolbachia sequences integrated into the D. ananassae genome are minor contributors (0.02%). Both D. melanogaster and D. ananassae F-element genes exhibit distinct characteristics compared to D-element genes (e.g., larger coding spans, larger introns, more coding exons, and lower codon bias), but these differences are exaggerated in D. ananassae. Compared to D. melanogaster, the codon bias observed in D. ananassae F-element genes can primarily be attributed to mutational biases instead of selection. The 5′ ends of F-element genes in both species are enriched in dimethylation of lysine 4 on histone 3 (H3K4me2), while the coding spans are enriched in H3K9me2. Despite differences in repeat density and gene characteristics, D. ananassae F-element genes show a similar range of expression levels compared to genes in euchromatic domains. This study improves our understanding of how transposons can affect genome size and how genes can function within highly repetitive domains.
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