Hoofdstuk 4 Flashcards
One key difference between structural imaging methods and functional imaging methods
- structural imaging is based on the fact that different types of tissue (skull, greymatter, whitematter, cerebrospinal fluid) have different physical properties
- these properties can be used to construct detailed static maps of the physical structure of the brain
- CT= Computerized Tomography
- MRI = Magnetic Resonance Imaging
Functional Imaging is based on the assumption that
neural activity produces local physiological changes in that region of the brain
- produce dynamic maps of the moment-to-moment activity of the brain, when engaged in cognitive tasks
Structural Imaging
measures of the spatial configuration of different types of tissue (CT/MRI)
Functional Imaging
measures temporary changes in brain physiology associated with cognitive processing (fMRI - based on a hemodynamic measure)
CT = Computerized Tomography
constructed according to the amount of x-ray absorption in different types of tissue
- amount of absorption is related to tissue density
MRI
better spatial resolution, which allows the folds of individual gyri to be discerned
- beter onderscheid white/grey matter
- adapted for use in detecting the changes in blood oxygenation (associated with neural activity) “functional MRI”
Strength of magnetic field is measured in Tesla
gemiddelde scanner 1,5T - 3 T, maar bestaat ook 7T
T1 relaxation time
variations in the rate at which the protons return back to the aligned state following the radio frequency pulse = can be used to distinguish between different types of tissue
PET (Position Emission Tomography)
measure bloodflow to a region directly
- need administration of radioactive tracer
PET/fMRI/fNIRS
hemodynamic methods
VBM
Voxel Based Morphometry
- voxel = volume-based unit (pixel = 2D)
Spatial Resolution fMRI (1mm depending on the size of the voxel)
DTI
Diffusion Tensor Imaging
Fractional Anistropy
FA
- a measure of the extent to which diffusion takes place in some directions more than others
The component of the MRsignal that is used in fMRI
is sensitive to the amount of deoxyhemoglobin in the blood
BOLD
Blood-Oxygen Level-Dependent Contrast
- the way that the BOLD signal evolves over time in response to an increase in neural activity (Hemodynamic Response Function HRF)
1) initial Dip
2) Overcompensation
3) Undershoot
fNIRS measures the bold signal by sending “light”of a particular wavelength to the brain (near infrared)
- more portable and tolerant of movement
- shallow neural activity
Cognitive subtraction
experimental design in functional imaging in which activity in a control task is subtracted from activity in an experimental task
Pure Insertion/Pure Deletion
the assumption that adding a different component to a task does not change the operation of other components = main problem with cognitive subtraction
the method of cognitive conjunction
requires that one is able to identify a set of tasks that have a particular component in common
Efference Copy
a motor signal used to predict sensory consequences of an action (perceptual system knows what to expect)
The main difference between a parametric design and a categorical design
is that in a parametric design, the variable of interest is treated as a continuous dimension rather than a categorical distinction
- one is measuring ASSOCIATIONS between brain activity and changes in the variable of interest, rather than
- measuring DIFFERENCES in brain activity between 2 or more conditions
(one is likely to use correlations to analyze data collected using a parametric design)
Functional Integration
the way in which different regions communicate with each other
- measuring functional integration: resting state paradigms (finding networks in a rested state
Default Mode Network
a set of brain regions that is more hemodynamically active during rest than during tasks
Central Problem in the analysis of functional imaging data
is how to deal with individual differences
- location of sulci can differ by a centimeter or more
- stereotactic normalization: mapping of individual differences in brain anatomy onto a standard template, followed by smoothing
Smoothing = redistributing brain activity from neighbouring voxel to enhance the signal-to-noise ratio
False Discovery Rate
generate thousands of random brain images (e.g. permuting the data) and select a threshold (p>0.05) based on random data sets
Family Wise Error (FWE)
correcting many statistical comparisons based on the number of tests being conducted
Functional Imaging signals are assumed to be correlated with the metabloic activity of neurons, and synapses in particular
neurons can be metabolically active by inhibitory interactions (when the presynaptic neurons are active, postsynaptic switched off), or by excitatory interactions (preynaptic off, postsynaptic on)
Activation and deactgivation
Asimply refer to the sign (positive or negative of the difference in signal between 2 conditions)
Semantic Dementia
Functional Lesion primarily in the semantic memory system that stores the meaning of words and objects
Multi-Voxel Pattern Analysis (MVPA)
examine the pattern of activation over a distributed set of voxels to enable a more fine grained approach
