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T?* mapping and B? orientation-dependence at 7 T reveal cyto- and myeloarchitecture organization of the human cortex.

ABSTRACT: Ultra-high field MRI (? 7 T) has recently shown great sensitivity to depict patterns of tissue microarchitecture. Moreover, recent studies have demonstrated a dependency between T?* and orientation of white matter fibers with respect to the main magnetic field B?. In this study we probed the potential of T?* mapping at 7 T to provide new markers of cortical architecture. We acquired multi-echo measurements at 7 T and mapped T?* over the entire cortex of eight healthy individuals using surface-based analysis. B? dependence was tested by computing the angle ?(z) between the normal of the surface and the direction of B?, then fitting T?*(?(z)) using model from the literature. Average T?* in the cortex was 32.20 +/- 1.35 ms. Patterns of lower T?* were detected in the sensorimotor, visual and auditory cortices, likely reflecting higher myelin content. Significantly lower T?* was detected in the left hemisphere of the auditory region (p<0.005), suggesting higher myelin content, in accordance with previous investigations. B? orientation dependence was detected in some areas of the cortex, the strongest being in the primary motor cortex (?R?*=4.10 Hz). This study demonstrates that quantitative T?* measures at 7 T MRI can reveal patterns of cytoarchitectural organization of the human cortex in vivo and that B? orientation dependence can probe the coherency and orientation of gray matter fibers in the cortex, shedding light into the potential use of this type of contrast to characterize cyto-/myeloarchitecture and to understand the pathophysiology of diseases associated with changes in iron and/or myelin concentration.

SUBMITTER: Cohen-Adad J

PROVIDER: S-EPMC3442114 | biostudies-other | 2012 Apr

REPOSITORIES: biostudies-other

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T₂* mapping and B₀ orientation-dependence at 7 T reveal cyto- and myeloarchitecture organization of the human cortex.

Cohen-Adad J J Polimeni J R JR Helmer K G KG Benner T T McNab J A JA Wald L L LL Rosen B R BR Mainero C C

NeuroImage 20120115 2

Ultra-high field MRI (≥ 7 T) has recently shown great sensitivity to depict patterns of tissue microarchitecture. Moreover, recent studies have demonstrated a dependency between T₂* and orientation of white matter fibers with respect to the main magnetic field B₀. In this study we probed the potential of T₂* mapping at 7 T to provide new markers of cortical architecture. We acquired multi-echo measurements at 7 T and mapped T₂* over the entire cortex of eight healthy individuals using surface-ba ...[more]

PMID: 22270354

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Project description:Motion boundaries (local changes in visual motion direction) arise naturally when objects move relative to an observer. In human visual cortex, neuroimaging studies have identified a region (the kinetic occipital area [KO]) that responds more strongly to motion-boundary stimuli than to transparent-motion stimuli. However, some functional magnetic resonance imaging (fMRI) studies suggest that KO may encompass multiple visual areas and single-unit studies in macaque visual cortex have identified neurons selective for motion-boundary orientation in areas V2, V3, and V4, implying that motion-boundary selectivity may not be restricted to a single area. It is not known whether fMRI responses to motion boundaries are selective for motion-boundary orientation, as would be expected if these responses reflected the population activity of motion-boundary-selective neurons. We used an event-related fMRI adaptation protocol to measure orientation-selective responses to motion boundaries in human visual cortex. On each trial, we measured the response to a probe stimulus presented after an adapter stimulus (a vertical or horizontal motion-boundary grating). The probe stimulus was either a motion-boundary grating oriented parallel or orthogonal to the adapter stimulus or a transparent-motion stimulus. Orientation-selective adaptation for motion boundaries--smaller responses for trials in which test and adapter stimuli were parallel to each other--was observed in multiple extrastriate visual areas. The strongest adaptation, relative to the unadapted responses, was found in V3A, V3B, LO1, LO2, and V7. Most of the visual areas that exhibited orientation-selective adaptation in our data also showed response preference for motion boundaries over transparent motion, indicating that most of the human visual areas previously shown to respond to motion boundaries are also selective for motion-boundary orientation. These results suggest that neurons selective for motion-boundary orientation are distributed across multiple human visual cortical areas and argue against the existence of a single region or area specialized for motion-boundary processing.

Dataset Information

T?* mapping and B? orientation-dependence at 7 T reveal cyto- and myeloarchitecture organization of the human cortex.

Publications

T₂* mapping and B₀ orientation-dependence at 7 T reveal cyto- and myeloarchitecture organization of the human cortex.

Similar Datasets

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