6. Cognitive Neuroscience Methods Flashcards
What is cognitive neuroscience?
combines cognitive psychology with neuroscience
- the study of how the brain structures and processes mediate cognitive behaviour
What are the challenges of cognitive neuroscience?
- assesses complex systems: around 1million neurons in 1 cubic mm of the brain
- signal to noise ratio (needle in a haystack)
- individual differences
What is the underlying principle of MRI?
- hydrogen atoms are like constantly spinning magnets
- they align when in a scanners magnetic field
- then, a radio wave is sent to make them face in a new direction
- signal disappears and they then relax and return to their previous alignment
- they emit energy when they do this
- this energy is what the scanner uses to create an image
How do MRI scans work?
- hydrogen atoms in different tissues have different relaxation times and can be identified separately
- the lower the water content of an area = the fewer hydrogen atoms emitting signals
- the weaker the signal, the darker the area appears on the scan
What are the advantages of MRI?
- high spatial resolution
- can view the brain from multiple angles
- non-invasive
- good at looking at soft tissue
What are the disadvantages of MRI?
- no temporal information (just an image)
- noisy, have to stay still and claustrophobic
- expensive
How do MRIs and fMRIs compare?
fMRIs…
- based on technique of MRIs (using magnets and radio waves)
- also look at function
How do fMRIs work?
- based on technique of MRIs (using magnets and radio waves)
- but are interested in blood flow in the brain as an indicator of activity
- blood contains haemoglobin which contains iron (magnetic)
- deoxygenated blood is affected differently by a magnetic field
- active parts of the brain contain more oxygen-rich blood
- by measuring the BOLD (blood oxygen level dependant) response in the scanner we can work out which parts of the brain are active
What do diamagnetic and paramagnetic mean?
How does this relate to haemoglobin?
diamagnetic = weak magnetic field: oxygenated
paramagnetic = strong magnetic field: deoxygenated
What are the advantages of fMRI?
- good spatial resolution
- okay temporal resolution
- non-invasive
- tells us which part of the brain is used in tasks
What are the disadvantages of fMRI?
- BOLD isn’t a direct measure of activity
- noisy, claustrophobic, have to stay still
- no metal based equipment can be used for stimulus presentation
What is positron emission tomography (PET scans)?
- similar to fMRI
- measures blood flow in the brain
- a mildly radioactive drug is injected/inhaled/swallowed
- this is absorbed into the bloodstream
- measures how much tracer goes where in the brain
- higher levels of activity show up as bright spots
- can be used to evaluate certain brain disorders e.g tumours
What are the advantages of PET?
- reasonable structural resolution
- direct reflection of activity
- more comfortable experience than MRI/fMRI
What are the disadvantages of PET?
- no temporal resolution
- expensive
- injection of radioactive materials: ethical issues
- may need to do MR or CT scan alongside
What is an overview of EEG (electroencephalography)?
- measures electrical signals generated by the brain through electrodes placed at the scalp
- they are produced by partial synchronisation of cortical field activity and are measured as changes in voltage, recorded at the scalp over time
How are EEG signals detected?
- electrodes are placed at scalp, connected with gel or conductive solution
- EEG signals are transported to an amplifier
- amplifier measures the difference in voltage between the active electrode and a reference electrode
What are the advantages of EEG?
- very good temporal resolution
- direct reflection of activity
- not claustrophobic, can even be used by infants
What are the disadvantages of EEG?
- poor spatial resolution
- motion artifacts
- how can we be sure which brain regions generated the electrical activity?
How does a magnetoencephalogram work? (MEG)
- pyramidal cells of the cortex, generate a significant magnetic field when active
- MEG records these magnetic fields
What are the advantages of MEG?
- excellent temporal resolution
- direct reflection of activity
- good spatial resolution
What are the disadvantages of MEG?
- expensive
- how can be sure which brain regions generated the electrical activity?
What did lesion patient Phineas Gage show?
- no impairment of language, intelligence, movement or memory
- he however had irresponsible, disregard for social conventions
What is transcranial magnetic stimulation (TMS)?
- uses a changing magnetic field to induce weak electrical currents in the cortex
- non-invasive causing depolarisation/hyperpolarisation of neurons in the brain
- can produce a stimulated temporary ‘lesion’ of a brain region by preventing normal function of that region
What are the advantages of TMS?
- near portable
- can stimulate lesion
