NeuroImage
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Psychological and neurophysiological models of visual processing have traditionally emphasized hierarchical models to explain how separate features of visual stimuli are combined. This concept has been challenged recently with the demonstration of simultaneous activation of multiple visual areas and rapid feedback to primary cortices. Here, we show human visual processing may involve similar mechanisms. ⋯ These enhanced early responses were followed by task-specific sustained posterior activity (300-500 ms). Faster reaction times were correlated with enhanced and faster early processing in the visual ventral areas. These data demonstrate the human visual system conjoins features rapidly, accelerating and amplifying the processing of relevant stimulus dimensions.
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Functional MRI (fMRI) in established Alzheimer's disease (AD) shows regionally altered blood oxygenation level dependent (BOLD) responses. Mild cognitive impairment (MCI) is thought to represent an intermediate state between health and early Alzheimer's disease. To study this probable early dementia stage pathology, we studied in detail the BOLD response in MCI during visual encoding. 28 MCI patients, 18 AD patients, and 41 healthy elderly controls performed a face encoding task during fMRI scanning. ⋯ This study stresses the importance of analyzing early phase BOLD responses and not only using one model of the BOLD response in neurodegenerative diseases. The increasing delay of the BOLD response from controls to MCI to AD may be consistent with the idea that MCI is a transitional state between healthy aging and dementia. Analyzing differences in different phases of the BOLD response introduces new opportunities to understand changes in regional brain dynamics in MCI and how well this may serve as an early marker of AD pathology.
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Comparative Study Clinical Trial
The relationship between whole brain volume and disability in multiple sclerosis: a comparison of normalized gray vs. white matter with misclassification correction.
We used SPM99 to obtain normalized whole brain volumes of gray matter, white matter, and total parenchyma in patients with multiple sclerosis (MS) (n = 41) and age-/sex-matched normal controls (n = 18). As SPM99's automated gray/white matter volumes were significantly influenced by tissue compartment misclassification due to the effect of MS-related brain lesions, we corrected these automated volumes for misclassification before performing our primary analyses. ⋯ Gray matter atrophy was related to clinical status (EDSS, 25FTW, and disease duration), lesion load (T1LV and FLLV), and central brain atrophy (TVW and BCR), whereas white matter atrophy was related to only central brain atrophy. These findings suggest that gray matter loss is related to other aspects of brain pathology and has more clinical relevance than white matter atrophy in MS.
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The spinal cord is frequently involved in multiple sclerosis (MS), and cord damage may be an important contributor to disability. Diffusion tensor magnetic resonance imaging (DT-MRI) provides quantitative information about the structural and orientational features of the central nervous system. In order to assess whether diffusion tensor-derived measures of cord tissue damage are related to clinical disability, mean diffusivity (MD) and fractional anisotropy (FA) histograms from the cervical cord were acquired from a large cohort of MS patients. ⋯ The multivariate linear regression model retained average cord FA and average brain MD as variables independently associated with disability, with a correlation coefficient of 0.73 (P < 0.001). DT-MRI reveals a loss of cervical cord tissue structure in MS patients. The strong correlation found between a composite DT-MRI score and disability suggests that a full and accurate assessment of cervical cord damage in MS provides information that usefully contributes to an explanation of the clinical manifestations of the disease.
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We have previously proposed a statistical method for extracting a plasma time-activity curve (pTAC) from dynamic PET images, named EPICA, for kinetic analysis of cerebral glucose metabolism. We assumed that the dynamic PET images consist of a blood-related component and a tissue-related component which are spatially independent in a statistical sense. The aim of this study is to investigate the utility of EPICA in imaging total distribution volume (DVt) and binding potential (BP) with Logan plots in a neuroreceptor mapping study. ⋯ The BPs estimated using EPICA were evaluated in 18 subjects by ROI-based comparison with those obtained using the nonlinear least squares method (NLSM). The calculated BPs were identical to the estimates using NLSM in each subject. We conclude that EPICA is a promising technique that generates parametric images of DVt and BP in neuroreceptor mapping without requiring arterial blood sampling.