Neuroimaging and Reward Flashcards
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
What does the nigrostriatal dopamine circuit do for the reward system?
- Reinforces sensory-motor associations
- Important in learning new skills
- Important in forming habits
- Disordered in addiction
What is reinforcement learning?
Learning the strategy to be taken in a given situation that maximises the chance of a successful outcome.
- Strategy stored for later selection
- Reinforcement makes the strategy more likely to be selected in a similar situation in the future.
Which hormone is released in response to a rewarding stimuli such as food or sex?
Dopamine
What can increase the strength of synapses from the cortex?
Release of dopamine into the striatum after cortical activity.
Long Term Potentiation
What are the consequences of high levels of dopamine at the wrong times?
Strengthening of synapses that reinforce actions that are not useful.
Results in disordered motor reinforcement.
Define addiction
Repeated use of an addictive substance that persists despite serious harmful consequences to an individual and significant problems in their life.
Define psychological dependence
A condition which develops when taking a drug produces a pleasurable state.
A person is motivated to take the drug in order to maintain a pleasurable state or to avoid discomfort.
What is the common pathway for all addictions?
Enhanced dopamine release/reduced reuptake.
What are the 4 branches of neuroethics?
- Scientific and Clinical integrity
- Autonomy
- Privacy
- Identity
Define Autonomy
Having the freedom to determine one’s own actions and behaviours
Define Informed Consent
Informed = weighing benefits against potential side effects or consequences
Consent = agree without coercion
What principles follow Autonomy?
Informed consent and equity
Define the anticipation problem in neuroethics.
Giving unrealistic expectations for the treatment
What is the principle of identity in neuroethics?
Effects of a treatment on a person.
- Will the treatment change who they are?
- Will a treatment restore their old self?
- Changes to a person post neuromodulation/stroke personality change
Define the desperation problem in neuroethics.
Vulnerable people are prone to false estimations of possible benefits and harms of a treatment
Define privacy and data protection in neuroethics.
Obligation to maintain privacy of people’s data
Define equity in neuroethics.
Equity between people for access to and application of treatments. Depriving others of treatment is violation of autonomy
