L7+8- fMRI & Neurophysiology

What is the primary advantage of MRI in brain studies?

High spatial resolution, capable of resolving fine cortical maps.

How does the temporal resolution of EEG/ERPs compare to MRI?

EEG/ERPs have excellent temporal resolution (milliseconds), while MRI has lower temporal resolution.

What is the main goal of structural MRI?

To study brain anatomy, abnormalities, development, and plasticity.

What significant recognition did MRI receive in 2003?

The Nobel Prize awarded to Mansfield & Lauterbur for their contributions to MRI.

What is the core principle behind MRI?

It relies on the contrast between different tissue types (gray matter, white matter, CSF).

What does fMRI primarily measure?

Blood flow changes related to neural activity in activated brain areas.

What is the BOLD effect in fMRI?

Differences in MR signal caused by varying levels of oxy- vs deoxy-hemoglobin during neuronal activation.

What are the three main challenges for fMRI experiments?

1. Measuring neural activity indirectly via blood flow changes. 2. Generating functional contrast. 3. Identifying functional contrast in raw data.

What is the purpose of the motor cortex activation study in fMRI?

To map brain areas responsible for specific movements (e.g., foot, finger).

What is the significance of T2* signal in fMRI?

It decays over time and is influenced by hemoglobin oxygenation, affecting the MR signal.

How does oxy-hemoglobin affect the BOLD signal?

Oxy-hemoglobin is diamagnetic and leads to slower T2* decay, resulting in a higher MR signal.

What is a key challenge in measuring the BOLD response?

The BOLD response is slow compared to neural activity, requiring careful experimental design.

What is a simple design in fMRI experiments?

Long gaps between stimuli to avoid overlap, but it can lead to participant fatigue.

What is the advantage of block design in fMRI?

It boosts signal and statistical power by grouping same-category trials.

What is the disadvantage of event-related designs in fMRI?

They have lower sensitivity compared to block designs due to overlapping BOLD responses.

What are the general aims of fMRI experimental design?

1. Optimize functional contrast to noise ratio. 2. Ensure measurement of contrast of interest. 3. Minimize experiment duration.

What is the first step in the analysis pipeline for identifying activated brain areas in fMRI?

Motion correction to correct for participant movement.

What does coregistration in fMRI analysis involve?

Aligning functional scans with anatomical scans.

What is the purpose of normalization in fMRI analysis?

To warp individual scans to a standard template for comparison.

What is the purpose of motion correction in fMRI?

To realign images to a reference volume and ensure accurate detection of functional contrast.

What does coregistration in fMRI involve?

Aligning functional images with the participant's structural MRI for easier interpretation.

What is the goal of normalization in group-level fMRI analysis?

To align activation maps from multiple participants to a common template for average activation pattern identification.

What is spatial normalization in the context of fMRI?

The process of ensuring MR images are in the same coordinate system as the atlas, such as Talairach-Tournoux.

What is the significance of the anterior commissure in spatial normalization?

It serves as a reference point for aligning MR images with an atlas.

What is the purpose of statistical analysis in fMRI activation studies?

To quantitatively identify brain regions showing activation, replacing visual inspection.

What is the General Linear Model (GLM) used for in fMRI?

To perform voxel-by-voxel statistical tests comparing observed MR signals to predicted timecourses.

What is a significant challenge in whole-brain fMRI analysis?

Low statistical power due to the large number of voxels, increasing the risk of Type I errors.

How does noise impact fMRI statistical results?

Different noise levels can cause two regions with the same true activation to appear differently active.

What is the BOLD signal in fMRI?

A T2* signal reflecting the ratio of oxy- to deoxy-hemoglobin, used to measure neural activity.

What are block and event-related paradigms in fMRI?

Experimental designs used to elicit reliable BOLD responses during fMRI studies.

What does the term 'somatotopic organization' refer to in fMRI studies?

The spatial arrangement of brain areas corresponding to different body parts, such as medial activation for feet and lateral for fingers.

What is the purpose of neuropsychological lesion studies?

To study brain function by comparing patients with brain lesions to healthy controls.

What is a limitation of neuropsychological lesion studies?

Temporal resolution is limited as they infer function from deficits rather than measuring real-time activity.

What is hemineglect syndrome?

A condition where patients fail to process visual information on one side, despite no visual field loss.

What tasks illustrate the deficit in hemineglect syndrome?

The Albert task (cancelling lines) and the line bisection task (marking the midpoint of lines).

What anatomical basis is associated with hemineglect syndrome?

Lesions at the right temporo-parietal junction, which contributes to spatial attention.

What is the goal of linking brain anatomy to behavior in neuropsychology?

To understand how structural and functional anatomy relates to behavioral functions after lesions.

What types of imaging are used to identify lesion sites in neuropsychology?

CT and MRI for structural anatomy, and fMRI and EEG for functional localization.

What is the primary goal of behavioral testing in neuropsychology?

To identify impaired versus spared functions.

What are the two main integration goals in neuropsychological testing?

1) Localize impaired behaviors to damaged regions. 2) Confirm preserved skills are not dependent on damaged regions.

What is a caveat when localizing impaired behaviors?

Lesions may affect a relay station, not the original functional region.

What does the term 'association' refer to in neuropsychology?

Damage to a region produces multiple deficits, indicating a syndrome.

What is 'dissociation' in the context of neuropsychology?

Damage impairs one task while leaving another intact, indicating functional specialization.

What syndrome is typically caused by bilateral parieto-occipital lesions?

Balint's Syndrome.

What is 'simultanagnosia'?

The inability to perceive more than one object at a time in a visual scene.

What is 'oculomotor apraxia'?

Difficulty making purposeful eye movements.

What is 'optic ataxia'?

Impaired visually guided reaching, unable to accurately reach for or grasp objects.

What does Balint's Syndrome illustrate about brain damage?

It shows an association of symptoms where multiple impairments co-occur due to a single lesion.

What is the significance of Patient DF in neuropsychology?

Patient DF demonstrates a dissociation between vision for action and vision for perception.

What is the main finding from the visuomotor posting task performed by Patient DF?

DF performs accurately, indicating preserved vision for action.

How did Patient DF perform in the perceptual matching task?

DF's responses were random, indicating impaired vision for perception.

What is a double dissociation in neuropsychology?

When two tasks rely on separate neural networks, evidenced by one task being impaired while the other is intact.

What are the two pathways associated with visual processing?

1) Occipito-temporal pathway for vision for recognition (perception). 2) Occipito-parietal pathway for vision for action.

What does the dorsal stream support?

Visually guided action.

What does the ventral stream support?

Object and form recognition.

What is the implication of finding a double dissociation between DF and RV?

It provides strong evidence for separate neural circuits for perception and action.

What are some limitations of neuropsychological methods?

Variability in pathology, lesion visibility, poor temporal resolution, and modularity assumptions.

What does the modularity assumption in neuropsychology suggest?

It assumes damage to one region does not affect others, which may not always be true due to brain reorganization.

What is a challenge with single-patient studies in neuropsychology?

They provide weak inference due to variability in individual cases.

What can small lesions in strategic locations cause?

Severe deficits despite their size.

What is diaschisis in neuropsychology?

A condition where some brain regions may be inactive due to disconnection from damaged areas.

What is the key point regarding functional and anatomical separation in visual processing?

Separation exists from the retina through cortical stages, not only in extrastriate cortex.

What does the finding of separate pathways in the extrastriate visual cortex imply?

Functionally distinct visual processes are supported by anatomically distinct circuits.