Neuroimaging and Reward Flashcards
(41 cards)
What are the three methods for neuroimaging?
CT, MRI and PET.
What is the principle of CT neuroimaging?
X-rays are absorbed to different degrees by different tissues of different densities. CT makes very thin slices of density readings.
What are the relative densities of the head in a CT scan?
- Air = Darkest
- Fat
- CSF
- WM
- GM
- Blood from haemorrhage
- Bone = Brightest
What is the principle of Positron Emission Tomography (PET)?
Radiation that is emitted from a radioisotope injected intravenously is registered by external detectors.
Used to highlight areas of increased glucose metabolism (cancers)
What does MRI actually measure?
Time it takes for hydrogen atoms to recover their alignment and spin after the radiofrequency pulse is turned off.
Hydrogen ions in different tissues takes different amounts of time to recover.
What tissues have the fastest and slowest recovery times in MRI?
Fat = fastest (brightest)
WM
GM
CSF = slowest (darkest)
What does T1 weighted MRI highlight and what does it measure?
T1 good for highlighting fat by measuring the recovery time for the magnetic alignment of the hydrogen atoms to return to resting alignment.
What does T2 weighted MRI highlight and what does it measure?
T2 good for highlighting water by measuring recovery time for the axial spin of the hydrogen atoms to return to resting state after the radio-frequency pulse is turned off.
What is a T2-FLAIR?
Fluid Attenuation Inversion Recovery. Used to distinguish between free flowing fluid and non free flowing like in oedema.
What is Anisotropy?
The degree to which hydrogen ions travel along white fibre bundles. Used as a measure of white fibre bundle integrity.
What is Isotropic, Anisotropic and Fractional Anisotrophy?
Isotropic (0) = hydrogen ions not constrained
Anisotropic (1) = hydrogen ions constrained
Fractional Anisotropy (0-1) degree of white matter integrity
What is the BOLD signal in T2 weighted imaging?
Blood-Oxygen-Level-Dependent Signal.
Which molecule can disrupt the MRI signal?
Deoxygenated haemoglobin - magnetic
What is Task Functional MRI?
T2 activity map while participant performs a task while in the scanner.
What are the major advantages of MRI?
- Detailed anatomical structure
- Detect pathology with anatomical precision
- Measure white matter integrity
- Ability to assess brain function and functional connectivity at rest and during tasks
- Doesn’t involve radiation, relatively safe and individuals can be repeatedly scanned.
What are the major disadvantages of MRI?
- Susceptibility to magnetic interference
- requires technical expertise to operate
- Diffusion and functional imaging are approximate but not a direct measure of white fibres integrity/functionality.
What makes MRI better than CT?
MRI has better anatomical contrast, can measure white matter integrity and measure brain function.
What makes MRI better than PET?
PET is anatomically poor, less available, requires radioactive tracer to be injected.
What advantage does PET have over MRI?
With PET we can quantify metabolic or molecular processes.
What advantage does CT have over MRI?
Ability to visualise bone or acute tissue bleeding.
What is a brain system?
A collection of structures in the brain that work together to perform a common function.
What is the difference between specific and generic function?
Specific - Info input to specific motor output
Generic - information input received from regions performing widely differing specific functions to perform a particular behaviourally important operation.
Why is the reward system a generic processing system?
It integrates information from many areas serving different functions and selects a behavioural response.
What does the mesolimbic dopamine circuit do for the reward system?
Inputs from hippocampus to integrate memory of ‘context’
Inputs from the amygdala to integrate memory of an emotional situation
