Quiz: High Resolution Applications: Cortical Layers, Polimeni

1. How many cortical layers are there in the human cerebral isocortex?
- a. There are exactly 6 well-defined layers throughout the entire isocortex
- b. There are 6 main layers throughout the entire isocortex but there are also well-defined sublayers whose appearances vary across areas
- c. The basic 6-layer structure is roughly present across isocortex, however the number of layers and sublayers that can be distinguished varies between areas and differs between histological stains
- d. The number of layers in the human isocortex is under debate and currently unknown
- e. The number of layers in the human isocortex depends on age and changes across the lifespan
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2. How well do the various functional and anatomical definitions of cortical layers agree?
- a. The layers are well-defined functional and anatomical units and the definitions based on these features agree perfectly.
- b. Layers can be defined based on anatomical features (such as cytoarchitectonics or myeloarchitectonics) or on functional properties, and while there can be rough agreement between various definitions and layer boundaries there is not a strict one-to-one correspondence.
- c. The functional and anatomical definitions are completely independent, have different boundaries, and generally do not agree.
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3. Why is it challenging to know which cortical layer or layers is/are being sampled from a given fMRI voxel?
- a. Current fMRI voxel sizes are too large to resolve individual layers and so the fMRI signal from any given voxel represents a mixture of activation across multiple layers.
- b. Current anatomical MRI voxel sizes are too large to reliably detect cortical layers in vivo, therefore their positions must be inferred from other features such as the geometry of the folding pattern, making it difficult to know which exact layers are being sampled from an fMRI voxel.
- c. The positions of the layers shift within the cortex with the folding pattern, making the estimation of layer position within the cortex challenging.
- d. All of the above
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4. What is the influence of the “draining vein” effect, which is well-known in BOLD fMRI (especially when using standard gradient-echo-based acquisitions), on the interpretation of laminar fMRI?
- a. Because intracortical veins drain deoxygenated blood up from the lower layers up to the brain surface, BOLD responses in upper layers will reflect pooled responses from all lower layers, causing a coupling across layers and potential mislocalization of laminar fMRI activity.
- b. BOLD signal changes near to the large pial vessels lying on the surface of the cortex are less specific than signal changes in the parenchyma, so removing the pial vessel contributions is sufficient for laminar fMRI.
- c. The draining vein effect is not a problem as long as the functional analysis utilizes appropriate individual Hemodynamic Response Functions for each cortical depth.
- d. The draining vein effect is not a problem as long as the voxel size is small enough to sample the BOLD signal across the cortical depths.
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5. What is the ultimate spatial resolution of human fMRI, defined as the spatial specificity of blood flow regulation in the human brain in response to neuronal activity?
- a. It is 1–3 mm, as measured by previous human fMRI studies.
- b. It is dictated by the spacing of the principle ascending intracortical venules, which is about 0.75–1 mm on average.
- c. It is dictated by the spacing of the principle descending intracortical arterioles, which is about 0.4–0.6 mm on average.
- d. It is equivalent to the spacing of the “vascular layers”, which is about 500 μm on average.
- e. It is matched to the spacing of the cell layers, which is about 100–300 μm on average.
- f. It is dictated by the spacing between the capillaries and the neurons, which is about 20–40 μm on average.
- g. It is currently unknown, since it depends both on the local vascular anatomy and spacing of the control structures, and therefore will likely vary across the cortex and between brain regions.
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