B&B 2/2 Flashcards
What are the 4 main methods of investigating the brain?
Lesion studies
Brain stimulation
Electrophysiology
Functional neuroimaging
What are the invasive and non-invasive ways of performing lesion studies?
Invasive - destroy brain regions of interest - remove/cool brain tissue Non-invasive - study people with incidental lesions - use brain stimulation to temporarily impair processing
How can we map lesions on the brain?
Using an MRI - allows spatial specificity and determination of causal relations
What was the case of HM?
A patient who had a lesion in the hippocampus as a result of surgery for epilepsy, found they could no longer form memories
What is a single dissociation lesion study?
Where a lesion in a specific region causes impairment in a specific task
What was the case of DF?
Suffered CO poisoning and acquired single dissociation btw dorsal and ventral stream, impaired object perception but still has object guided action (e.g. posting a letter)
What is the issue with using single dissociations to research the brain?
The tasks we are testing the participants with may not be equally as easy or may be testing the wrong skills for that region
What is double dissociation?
Different tests are carried out on different regions to prove that a specific region is associated with a task
What would a lesion in the ventral stream usually suggest?
impairment in discrimination
- cannot match the shape of two targets to get a reward
What would a lesion in the dorsal stream usually suggest?
impairment in location
- cannot discriminate the position of a probe relative to 2 targets
What are the Pros and Cons of lesion studies?
Pros
- reveal causal links between regions and functions
- high spatial precision
Cons
- low temporal precision
- low spatial precision (when incidental lesions)
- possible confounding impairment
- difficult, costly, (unethical) to experimentW
What is invasive brain stimulation?
stimulation of neurones in particular brain regions by implanting electrodes
What is non-invasive brain stimulation?
TMS used to stimulate neurones
tDCS can stimulate larger areas than TMS
What does stimulating face recognition areas of a participant’s face cause?
Participants see faces in objects that do not normally have faces
What does stimulating colour perception areas in the brain cause?
Participants see rainbow colours on single coloured objects
How does TMS work?
Stimulation coil produces fast changing magnetic fields over the scalp inducing electric currents into into neural tissue
What can stimulation of the visual cortex cause?
Phosphenes (light flashes)
What can stimulation of the motor cortex cause?
muscle twitches
Why is TMS described as chaotic?
There is no clear pattern of disruption of neurones
What are the Pros and Cons of brain stimulations?
Pros
- reveals causal links between brain regions and functions
- high temporal precision and reasonable spatial precision
- relatively easy + cheap
Cons
- underlying neural mechanisms not well understood
- widespread effects possible
- cannot reach all parts of the brain with TMS
What is electrophysiology?
The measuring of membrane potentials and neural firing by getting as close to the neurone as possible
What is invasive electrophysiology?
single neurones recordings
What is non-invasive electrophysiology?
EEGs and MEGs
What can we measure in animals using implanted microelectrodes?
find a neurone’s receptive field
probe the neurone with different visual stimuli
What is a low pass filter recording?
neural spiking from action potentials
What is high pass filter recording?
local field potentials from presynaptic inputs changing membrane potential
What can be done with the recordings once they have been isolated?
Track the occurrence of spikes over time and create a histogram
In what cases can invasive electrophysiology be done in humans? However, what is the issue with this?
In epileptic patients
However, they already have altered brain function
How do we use an EEG?
electrodes attached to the scalp using conductive gel
weak electrical signals are amplified and plotted across time creating a temporally precise map of cortical activations
How do we use MEG?
Evoke magnetic fields by generating electrical changes in the brain
Find the characteristic temporal patterns of electric currents
What are the 3 main states of electric currents in the brain?
delta waves (asleep) alpha waves (awake) gamma waves (sensory processing)
What is an ERP?
Event related potential - an accumulation of random neural responses
What are the Pros and Cons of electrophysiology
Pros - high temporal resolution - high spatial precision (if invasive) - easy/cheap - yields rich info about neural dynamics Cons - low spatial precision (if on scalp) - only correlational data - no direct access to neural scalp firing (if on scalp)
What does functional neuroimaging do?
track cerebral blood-flow to find high activation areas
What are the 3 types of functional neuroimaging?
PET
fMRI
fNIRs
What is a Pet scan?
fast decaying radioactive tracers are injected into the blood, resulting radiation is collected and spatially reconstructed to find a 3D image of where the tracer accumulates
What are some examples of tracers?
fluorodeoxyglucose (glucose-like, so accumulates where glucose would i.e. high metabolic activity)
What are some issues with PET?
exposes participants to radioactivity
does not offer anatomical mapping of the brain
temporally very imprecise
How does fMRI work?
particles in the body are magnetised and stimulated with radioactive frequency pulses
this energy resonates from the body creating the fMRI signal
What is the fMRI flow diagram?
increased neural activity –> increased blood-flow –> oxygen removed from blood –> deoxy/oxy haemoglobin imbalance –> increased signal
What can be said about the temporal precision of fMRI?
It is more precise than PET
It has several seconds of delay behind neural activations so not super precise
What are the Pros and Cons of fMRI?
Pros - high spatial precision - allows functional and structural mapping - mostly non-invasive Cons - low temporal precision: haemodynamic lag - only correlational data - indirect activation measure - quite expensive
What tracer is also used by PET used in Alzheimer studies?
PiB - binds to beta-amyloid
