fMRI ARTICLES (mini-quiz 6) Flashcards
An Introduction to fMRI & Neurophysiological investigation of the basis of the fMRI signal
What does fMRI stand for, and what does it measure?
Functional Magnetic Resonance Imaging; it measures changes in blood oxygen levels to infer neural activity.
What is the BOLD signal in fMRI, and what does it represent?
Blood Oxygen-Level Dependent signal; it reflects the changes in oxygenated and deoxygenated hemoglobin in the blood, indicating neural activity.
What are the two most common experimental designs used in fMRI studies?
Block designs and event-related designs.
How does the General Linear Model (GLM) help in analyzing fMRI data?
It correlates predicted neural responses with observed activity to identify task-related brain regions.
What is the importance of pre-processing in fMRI data analysis?
It corrects for artifacts, aligns data, and prepares it for further analysis, ensuring accuracy in results.
Explain the concept of voxel in the context of fMRI.
A voxel is a 3D pixel representing a volume element in the brain, with spatial resolution determined by voxel size.
What is the purpose of the ‘field map’ in fMRI sessions?
To measure the homogeneity of the magnetic field and correct distortions during data analysis.
What is a rapid event-related design, and what are its advantages?
An fMRI experimental design with shorter delays between trials, allowing for more efficient data collection.
What is spatial smoothing in fMRI, and why is it applied?
It’s a technique that averages data from neighboring voxels to reduce noise and enhance signal clarity.
What role does the hemodynamic response function (HRF) play in fMRI data interpretation?
It models the time course of the BOLD response to neural activation, crucial for data analysis.
Why is high temporal resolution not achievable in fMRI?
Due to the sluggish nature of the BOLD response, which lags behind actual neural activity.
What are some limitations of fMRI as a research tool?
Poor temporal resolution, indirect measurement of neural activity, and potential susceptibility to artifacts.
How does a block design differ from an event-related design in fMRI studies?
Block designs involve continuous tasks during blocks of time, while event-related designs have discrete trials with random timing.
What is meant by jittering in an event-related fMRI design?
Introducing random delays between stimulus presentations to ensure accurate statistical analysis.
Explain the difference between structural and functional MRI.
Structural MRI provides detailed images of anatomical structures, while functional MRI captures brain activity over time.
What is functional connectivity analysis in fMRI?
It identifies networks of brain regions that activate together, suggesting they are part of the same functional system.
What factors determine the choice of voxel size in fMRI studies?
Desired spatial resolution and the trade-off with temporal resolution and data acquisition time.
What are the advantages of using multivariate methods like Independent Component Analysis (ICA) in fMRI?
They can identify networks of event-related regions, offering insights into complex brain connectivity.
What are the most widely used software packages for fMRI data analysis?
SPM (Statistical Parametric Mapping) and FSL (FMRIB Software Library).
What is a free-running design in fMRI studies?
An experimental setup where events are presented continuously without structured breaks, like watching a movie.
What is the main focus of the study in Neurophysiological Investigation of the Basis of the fMRI Signal?
Understanding the relationship between fMRI signals and underlying neural activity.
What are Local Field Potentials (LFPs) and their significance in this context?
LFPs are low-frequency brain activity signals that correlate strongly with the BOLD response in fMRI.
What does MUA stand for, and what does it measure?
Multi-Unit Activity; it measures the spiking activity of multiple neurons.
How is the BOLD response related to LFPs according to the study?
The BOLD signal is more closely linked to LFPs, reflecting the input and local processing of an area.
What is the primary difference between LFPs and MUA in their contribution to fMRI signals?
LFPs provide a more sustained and consistent correlation with the BOLD signal than MUA.
How do haemodynamic changes reflect neural activity in fMRI?
Changes in blood flow and volume, detected by fMRI, are triggered by neural activity requiring more oxygen.
What imaging technique is commonly used in these neurophysiological studies to measure the BOLD response?
Echo-planar imaging (EPI).
Why are simultaneous intracortical recordings and fMRI crucial in these studies?
They allow for direct comparison between neural and haemodynamic responses, providing better understanding.
What did the study find regarding the temporal dynamics of the BOLD response?
The BOLD signal lags behind neural activation by approximately 2 seconds and reaches a plateau after about 7 seconds.
How does the spatial summation of LFPs and MUA differ?
LFPs integrate signals over a broader area (millimeters), while MUA is more localized (hundreds of microns).
What techniques are used to reduce noise when recording neural signals during fMRI?
Special electrodes and interference compensation systems to minimize artifacts from the magnetic field.
What role do visual stimuli play in neurophysiological experiments with fMRI?
They provide a controlled way to elicit and measure neural and haemodynamic responses.
What conclusions were drawn about the fMRI signal in terms of neural processing?
It likely represents input and local processing rather than direct neural output.
Why is the correlation between LFPs and BOLD responses higher than that with MUA?
LFPs capture more sustained neural activity, closely matching the slower BOLD signal.
What challenges are associated with mapping neural activity using fMRI?
The underestimation of neural activity due to the low signal-to-noise ratio of haemodynamic responses.
What impact does neural adaptation have on BOLD responses?
It can cause transient changes in neural signals, affecting the consistency of the BOLD response.
What was the significance of using high-contrast stimuli in the experiments?
To investigate how changes in stimulus intensity affect both neural and BOLD responses.
What methodological steps were taken to ensure the accuracy of neural signal recordings during fMRI?
Pre-whitening and filtering techniques to minimize correlations and enhance signal clarity.
What is the implication of the study for interpreting human fMRI experiments?
BOLD activation may reflect not just spiking output but broader synaptic and local processing activities.
Why is understanding the neurophysiological basis of fMRI signals important for neuroscience?
It provides deeper insights into how brain imaging results relate to actual brain function and structure.
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