Introduction and Neuroimaging methods 1 Flashcards
What are Marr’s 3 levels of analysis?
Computational - what is the problem that needs to be solved
Algorithmic - how can we solve the problem
Implementation - solving the problem
What does Marr’s doctrine of independence state?
You can analyse a problem at a given level without information about other levels
What is determinism and how does it relate to scientific study?
The belief that a whole is nothing but the sum of its parts
If you know all the parameters then you can predict what will happen
However most scientists have given up on this theory
What is emergence and how can we visualise it?
The belief that wholes are more than the sum of their parts
A heart pumps as a whole but this isn’t seen in individual cells
Shows that a system can exhibit properties not seen by its simpler form
What is multiple realizability and where can it be seen?
A system or function can be realized in many distinct forms
In music, a flute can play tone A, but a different mechanism (e.g. piano) can also produce tone A in a different way
The same could be true for consciousness
What is spatial and temporal resolution?
Spatial tells you how accurate an image is in terms of where it happens
Temporal tells you the exact point in time something happens
What are some examples that selective brain lesions lead to selective loss of functions?
Phineas gage - his personality, but not his intelligence, was altered when he had damage to his frontal lobe
Broca’s patient - damage to his left inferior frontal cortex led to aphasia (understood language but couldn’t speak)
What are some methods of lesion studies?
Physical lesions Pharmacological lesions (drugs) Reversible lesions (cooling parts of the brain, TMS)
What are the pros and cons of lesion studies?
Pros - they provide information about the function of different regions
Cons - not very precise, hard to interpret results, recovery processes are long
What is TMS and how does it work?
Transcranial Magnetic Stimulation
Uses magnetic fields to induce ‘virtual’ lesions
This occurs by placing a coil near the head which induces a current in the neurons
Can cause an activation (muscle response) or an inhibition (disrupt local activity)
What are two possible theories for striate (visual) cortex activation in blind braille readers?
After a sensory signal is sent to the thalamus, it either - Sends a parallel signal to the somatosensory and striate cortex
Sends a signal to the somatosensory cortex and then from there to the striate cortex
How was TMS used to measure striate (visual) cortex activation blind braille readers?
TMS was applied to temporarily inhibit parts of the cortex
If applied to the somatosensory cortex 10-30ms after a stimulus was presented then they were not good at identifying or detecting it
If applied to the striate cortex 40-70ms after a stimulus was presented then they were not good at identifying it but could detect it
What did the results of the TMS study of blind braille readers tell us about how the striate (visual) cortex works?
When the somatosensory cortex was lesioned it led to disruption of detection and identification
When the striate cortex was lesioned then there was only disruption in identification
Tells us the striate cortex gets a signal from the somatosensory cortex (hypothesis 2)
What are the pros and cons of TMS?
Pros - has excellent temporal resolution, have controlled lesions of specific brain regions
Cons - low spatial resolution, have lots of background noise, may have long-term effects
What is tDCS and how does it work?
Transcranial Direct Current Stimulation
Electric currents are used to stimulate brain regions and change cortical excitability
This is done through plus and minus poles on parts of the brain
What are some basic stimulations of tDCS?
Cathodal stimulation - negative voltage is used for hyperpolarization of neuronal membranes, which decreases firing rate and excitability
Anodal stimulation - positive voltage is used for depolarization of neuronal membranes, which increases firing rate and excitability
This polarization leads to short terms effects
What are the pros and cons of tDCS?
Pros - have controlled neuromodulation, can study healthy participants
Cons - low spatial resolution, can’t be used if on certain medication
What is PET and what does it do?
Positron Emission Tomography Radioactive material (such as oxygen, fluorine and nitrogen isotopes) are injected and go to areas of the brain that use them
How does PET work?
Radioactive isotopes naturally emit positrons when they decay
These positrons collide with electrons and emit photons in opposite directions
Detectors around participants measure these photons
What are the pros and cons of PET?
Pros - can measure blood flow, can be used when you’re on medication
Cons - very poor temporal resolution (measures over 45-60 second period), average spatial resolution
What is fMRI and what does it look like?
Functional Magnetic Resonance Imaging
Uses very big static magnets to scan brain
What does fMRI measure?
Oxygen concentration
Blood flow is increased when neurons become activated
This means there is higher oxygen concentration in areas that are activated
Therefore fMRI is an indirect measure of neural activity
What is the problem with fMRI being an indirect measure?
It measures blood flow change, but there may be some activity that doesn’t trigger blood flow change
It’s therefore not measuring the actual neural activity
What is the subtraction method?
Measuring the difference between an area active and the same area at rest
e.g. hand clenching and at rest
What are the pros and cons of fMRI?
Pros - high spatial resolution, good temporal resolution
Cons - expensive, can’t be used with participants with metallic devices
What are the main problems with fMRI?
The small size of the activation related response means it is susceptible to noise from movement
Neural events may be attributed to events other than they task they are about
How is the subtraction method used in simple RT tasks?
In one task the participant presses a key when they hear a tone
In the next, the participants will be presented with a high or low tone and must only press when high tone
Gives the time it takes to discriminate
