Lecture 6 - Cognitive Neuroscience Methods Flashcards
What is an fMRI?
Deoxygenated blood is affected by a magnetic field differently than oxygenated blood
When neurons are active, they burn energy. This is automatically replenished via oxygen carried by hemoglobin in the blood stream
Active parts of the brain contain more oxygen-rich blood
By measuring the BOLD (Blood Oxygen Level Dependent) response in the MRI scanner, we can work out which parts of the brain were active recently.
What is an MEG?
The pyramidal cells of the cortex, when active, generate a significant magnetic field
MEG records these magnetic fields.
For both EEG and MEG, the synchronous firing of 10k neurons is required to produce a field which is large enough to measure
Magnetic fields are less distorted by the scalp than electrical fields
What is an EEG?
EEG measures electrical signals generated by the brain thru electrodes placed at the scalp
EEG signals are produced by partial synchronisation of cortical field activity and are measured as changes in voltage, recorded at the scalp, over time
Analysis of EEG signals may be task dependent or task independent
What is a PET?
Poistron emission tomography
breakthrough brain functional imaging method
Measures blood flow in the brain - more blood flow in active areas
Inject, inhale or swallow a mildly radioactive drug (tracer) which is absorbed into the blood stream
Measure how much of tracer goes where in brain (via the postron emissions of the tracer)
Higher levels of activity show up as bright spots
Can also be used to evaluate certain brain disorders, such as tumours, Alzheimer’s disease and seizures
What is a TMS?
Transcranial magnetic stimulation (TMS)
Uses a changing magnetic field to induce weak electric currents in the cortex
Non-invasive method causing depolarisation or hyperpolarisation of neurons in the brain (ie decrease/increase activity)
Can produce a simulated temporary lesion of a brain region by preventing normal function of that region
Invested by Tony Barker and colleagues at University of Sheffield
What is Neuropsychology?
Lesion patients - eg Phineas Gage
Injured in 1840s
No impairment of language, intelligence. movement or memory
Irresponsible, disregard for social conventions
Gage was no longer Gage
What are the benefits and limitations of using an fMRI?
Benefits - good spatial resolution (get structural data within same session), reasonable temporal resolution, non-invasive, tells us which parts of the brain are used in tasks
Disadvantages - BOLD isn’t a direct measure of activity, and care should be taking interpreting it
Experience - noisy, gotta stay still, claustrophobic
Expensive
cant have any metal-based equipment for stimulus presentation
What are the benefits and limitations of using an EEG?
Very good temporal resolution
Direct reflection of activity
Not claustrophobic, can even be used by infants
DISADV -
poor spatial resolution, motion artifacts, inverse problem - how can we be sure which brain regions generated the electrical activity?
What are the benefits and limitations of using an MEG?
Excellent temporal resolution, Direct reflection of activity, Good spatial resolution (not distorted by scalp and for whole brain), especially if combined with MRI
Limitations -
Expensive
Inverse problem - how can we be sure which brain regions generated the electrical activity?
What are the cognitive neuroscience techniques?
F M E P T N
fMRI
MEG
EEG
PET
TMS
Neuropsychology
Where are neurons found?
In the cortex, limbic system and cerebellum
Long strands are in the axons which connect brain areas
What are terminal buttons?
Messages passed via neurotransmitters
What is an action potential?
Electrical signal initiated when the neuron fires
What is cognitive neuroscience?
Neuroscience plus cognitive psychology
Biological processes
Scientific study of the structure and function of the nervous system
Cognitive neuroscience is the study of how brain structures and processes mediate cognitive behaviour
What are some challenges for cognitive neuroscience?
Brain is a complex system
around 1 mill neurons in 1 cubic mm of brain
Issue of signal to noise ratio
- needle in a haystack
Between individual differences - different responses from people to task
- Experience/ individual variability ^
Within-individual differences
-strategy, mood, task difficulty (hunger)
What is an MRI scan?
Static structure of the brain
Hydrogen atoms in different tissues such as fat and water have different relaxation times and can be identified separately
The lower the water content of an area, the fewer hydrogen atoms there will be emitting signals
The weaker the signal, the darker the area appears on the scan
The result is shades of grey, fat is quite light, but bone is dark
What are some benefits of MRI scans?
- Excellent spatial resolution
- Allows you to view the brain from multiple angles
- Non-invasive
- Excellent for looking at soft tissue
What are some disadvantages of MRI?
- No temporal information
- Experience - noisy, gotta stay still, claustrophobic
- Expensive
- Older metal implants are not compatible
What is Piaget’s conservation of number task?
do the two rows of circles have the same number of dots in each row?
9 sec pause - allows time for BOLD response (4 sec)
found only 2.5% of the 5-6 year olds could conserve numbers
99.7% of the 9-10 year olds could conserve the numbers
BUT our brains process a vast amount of information and perform multiple tasks at the same time
How can we tell if the brain activity is purely related to conservation?
Provide a control experiment
What are the benefits and disadvantages of PET?
ADV - reasonable structural resolution
Direct reflection of activity
No motion artifacts
More comfortable experience than MRI, fMRI
DISADV- No temporal resolution
Expensive
Injection of (very weak) radioactive substance so ethical issues
May need to do MR or CT scan as well
How are EEG signals detected?
Electrodes are placed on the scalp, connected with gel or conductive solution
EEG signals are transported to an amplifier
The amplifier measures the difference in voltage between the active electrode and a reference electrode
What is Damasio et al - neuroimaging reconstruction
Demonstrated damage had been in the orbitofrontal and anterior medial areas of the frontal lobes
