cortex ARTICLE (mini-quiz 2) Flashcards
Laminar imaging of positive and negative BOLD in human visual cortex at 7 T
Define “Direction of Information Flow” in brain imaging.
The direction of information flow refers to the transmission pathway of neural signals between brain regions. It’s crucial for understanding brain connectivity and helps identify hierarchical connections, such as feed-forward (lower to higher) and feedback (higher to lower) pathways.
What are feed-forward and feedback connections in the visual cortex?
Feed-forward connections send signals from lower to higher brain areas (e.g., retina to V1), typically ending in the granular layers. Feedback connections go from higher to lower areas (e.g., V2 to V1), modulating sensory input by ending in supra- and infra-granular layers.
What does BOLD stand for in fMRI?
BOLD stands for Blood Oxygenation Level Dependent, a signal in fMRI that tracks brain activity by detecting changes in blood oxygen levels associated with neural activity.
Describe the main advantage of ultra-high field MRI scanners in brain research.
Ultra-high field MRI scanners (7 Tesla and above) provide sub-millimeter resolution, enabling visualization of fine-scale structures in the human cortex in vivo, bridging gaps between human and animal studies.
What is the stria of Gennari in the primary visual cortex (V1)?
The stria of Gennari is a dense band of myelinated fibers in V1, marking the input area from the retina and distinguishing V1 anatomically.
Define “excitatory” and “suppressive” processes in the context of BOLD signal response.
Excitatory processes increase neural activity and often correspond to positive BOLD signals, while suppressive processes decrease activity and may correspond to negative BOLD signals, both reflecting cortical layer functionality.
What is a “laminar profile” in brain imaging?
A laminar profile represents imaging data across different cortical depths, enabling analysis of activity within specific cortical layers from gray/white matter boundaries to the cortical surface.
Explain the significance of BOLD signals across cortical depths.
BOLD signals across cortical depths allow for analysis of layer-specific brain activity, aiding in the differentiation of excitatory and suppressive neural processes within the cortex.
Define “gradient echo BOLD fMRI” and one limitation in high-resolution imaging.
Gradient echo BOLD fMRI captures BOLD signals through magnetic field gradients. A limitation is susceptibility to artifacts from large pial veins, which may mask finer neural activity.
What methodological improvement did this study employ for fine-scale imaging in V1?
The study used 0.55 mm isotropic resolution with 3D gradient echo EPI and high-density surface coils, enabling detailed laminar BOLD profiles across V1.
Describe the significance of using a unilateral dartboard pattern in the study’s design.
The dartboard pattern produces distinct contra-lateral and ipsi-lateral BOLD responses, allowing separate examination of excitatory and suppressive processes across cortical depth.
Define “isotropic resolution” in fMRI.
Isotropic resolution means that voxel dimensions are equal in all directions, ensuring spatial consistency across cortical depths, crucial for detailed cortical mapping.
What is the “equi-volume model” and why is it used in cortical depth analysis?
The equi-volume model creates a coordinate system across cortical depths, accounting for cortical thickness variations, which enhances accuracy in depth measurement across convoluted cortex areas.
What challenges are associated with BOLD imaging at sub-millimeter resolution?
BOLD imaging at this scale faces challenges from cortical folding and variable thickness, complicating signal consistency and data interpretation.
How does the angle of cortical surface relative to B0 affect %BOLD signal changes?
The %BOLD signal changes depending on cortical surface orientation to B0 due to alignment with large pial veins, creating signal variability unrelated to neural activity.
What is “T1-weighted imaging” and its application in brain studies?
T1-weighted imaging highlights tissue contrast based on T1 relaxation times, improving visibility of myelin-rich areas and cortical structures in high-resolution studies.
What is the relationship between positive BOLD signal and synaptic activity?
Positive BOLD signals correlate with increased synaptic activity, reflecting metabolic demand and blood flow linked to local field potential increases.
How does a negative BOLD signal relate to neural suppression?
Negative BOLD signals indicate reduced neural activity, often reflecting inhibitory or suppressive processes in the imaged brain region.
How does cortical gyrification impact laminar profile imaging?
Cortical gyrification, or folding, affects imaging by creating cortical thickness and orientation variations, complicating uniform high-resolution data acquisition.
What was the primary objective of the visual cortex laminar profile study?
To map excitatory and suppressive BOLD responses across cortical depth in V1, using high-resolution imaging to understand layer-specific stimulus processing.
