NeuroImage
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The present study used functional magnetic resonance imaging to examine cortical specialization for letter processing. We assessed whether brain regions that were involved in letter processing exhibited domain-specific and/or mandatory responses, following Fodor's definition of properties of modular systems (Fodor, J. A., 1983. ⋯ These regions likely subserve some linguistically oriented cognitive process that is unique to letters, such as grapheme-to-phoneme translation or retrieval of phonological codes for letter names. Hence, cortical specialization for letters emerged in the naming task in some peri-sylvian language related cortices, but not in occipito-temporal cortex. Given that the domain-specific response for letters in left peri-sylvian regions was only present in the naming task, these regions do not process letters in a mandatory fashion, but are instead modulated by the linguistic nature of the task.
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In the complex regional pain syndrome (CRPS), several theories proposed the existence of pathophysiological mechanisms of central origin. Recent studies highlighted a smaller representation of the CRPS-affected hand on the primary somatosensory cortex (SI) during non-painful stimulation of the affected side. We addressed the question whether reorganizational changes can also be found in the secondary somatosensory cortex (SII). ⋯ Mean sustained, but not current pain levels were correlated with the amount of sensory impairment and the reduction in signal strength. We conclude that patterns of cortical reorganization in SI and SII seem to parallel impaired tactile discrimination. Furthermore, the amount of reorganization and tactile impairment appeared to be linked to characteristics of CRPS pain.
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Velocity-selective arterial spin labeling (VS-ASL) tags spins on a basis of flow velocity, instead of spatial distribution that has been commonly adopted in conventional ASL techniques. VS-ASL can potentially generate tags that are very close to the imaging plane and whereby avoid the error source of transit delay (deltat) variation independent of inflow time (TI). In practice, however, TI of VS-ASL should still be chosen with caution with respect to intravascular signal and cutoff velocity (V(c)). ⋯ For perfusion measurement in human brain, low V(c) (<4 cm/s) is recommended. With V(c) = 2 cm/s, quantitative cerebral blood flow is 72.8 ml/100 ml/min, which is in agreement with the reported range using conventional ASL methods. In field strength of 3 T, numerical simulation shows that optimal signal-to-noise ratio efficiency can be achieved with TR/TI = 2092 ms/1664 ms for single slice and 4493 ms/1404 ms for slab imaging.
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In vivo MRI-derived measurements of human cerebral cortex thickness are providing novel insights into normal and abnormal neuroanatomy, but little is known about their reliability. We investigated how the reliability of cortical thickness measurements is affected by MRI instrument-related factors, including scanner field strength, manufacturer, upgrade and pulse sequence. Several data processing factors were also studied. ⋯ The number of (single vs. multiple averaged) acquisitions had a negligible effect on reliability, but the use of a different pulse sequence had a larger impact, as did different parameters employed in data processing. Sample size estimates indicate that regional cortical thickness difference of 0.2 mm between two different groups could be identified with as few as 7 subjects per group, and a difference of 0.1 mm could be detected with 26 subjects per group. These results demonstrate that MRI-derived cortical thickness measures are highly reliable when MRI instrument and data processing factors are controlled but that it is important to consider these factors in the design of multi-site or longitudinal studies, such as clinical drug trials.
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Previous human imaging studies have revealed a network of brain regions involved in the processing of allodynic pain; this includes prefrontal areas, insula, cingulate cortex, primary and secondary somatosensory cortices and parietal association areas. In this study, the neural correlates of the perceived intensity of allodynic pain in neuropathic pain patients were investigated. In eight patients, dynamic mechanical allodynia was provoked and brain responses recorded using functional magnetic resonance imaging (fMRI). ⋯ This matches the representation of other clinical pain syndromes, confirmed by a literature review. In contrast, experimental pain in healthy volunteers resides predominantly in the cAI, as shown by the same literature review. Taken together, our data and the literature review suggest a functional segregation of anterior insular cortex.