electrophysiological recordings of brain activity Flashcards
what are 2 electrophysiological recordings techniques?
micro-electrode recordings: measures post-synaptic and action potentials
- highly invasive
- high temporal and spatial resolution
EEG/ERP: measures post-synaptic potentials
- non-invasive
- high temporal but low spatial resolution (can’t localise activity)
what are 2 metabolic recording techniques?
PET: measures indirect metabolic correlates of neural activity
- sort of invasive
- high spatial but low temporal
fMRI: measures indirect metabolic correlates of neural activity
- non-invasive
- high spatial but low temporal
describe micro-electrode recording?
what they measure?
how they measure?
strengths and weakness?
very thin electrodes inserted into brain tissue to measure electrical activity
measures ‘single-cell recordings’ (one neuron) and the firing rate of neurons (frequency of action potential generated)
only performed during surgery as highly invasive e.g brain
high temporal and spatial resolution and most direct & precise measure of brain activity
what did Quiroga and colleagues find?
many cells in the medial temporal lobe showed selective responses to a specific item (irrespective of size, view etc.)
also responded to the name of the person and famous buildings
describe EEG?
what sensitive and not sensitive to?
strengths and weakness?
- measure the summation of multiple local field potentials (LFPs) on the scalp which is presented as a voltage
- sensitive to activity in cortical tissue not so much further down in the scalp
- not sensitive to action potentials (spikes)
high temporal but low spatial resolution
non invasive
what are the 3 ways of analysing EEG data?
- how frequently singal oscillated in a certain amount of time (frequency)
- shape or frequency can inform on sleep pathways or pathologies e.g epilepsy
- segments can be analysed separately (ERPs)
what happens if you missed a night of sleep?
wouldn’t catch up on all the hours of sleep missed but catch up on all REM sleep missed (can detect this through the frequencies of EEG)
how can EEG be used to detect conscious awareness?
what has one study found about those in a vegetative state?
- high frequency of EEG activity associated with greater cortical actvitiy
- recorded high frequency over mortor cortex to assess conscious awareness of those in vegetative state
Cruse et al. found 3/16 activated the correct motor areas instructed suggesting presence of conscious awareness in these patients
what is a vegetative state?
no overt motor or verbal responses
no voluntary behaviour from upper and lower limbs
how can an EEG be used to measure epilepsy?
large amplitude discharges (due to excessive synchronisation of post-synaptic potentials) in those with epilepsy
discharges can be observed during seizures (ictal activity) or between seizures by EEG (inter-ictal activity)
describe ERPs?
method of analysing EEG recordings by extracting from the EEG segments time-locked to specific events (stimuli or responses)
how do you average segments of EEGs?
mean of reactions to stimulus over a multitude of trials
separate stimulus are separately averaged
how are ERP waves analysed?
- order - which number peak
- latency - timing after stimulus onset
- polarity - positive or negative
what is the relationship of N400 amplitude and semantics of a sentence?
amplitude is proportional to the predictability of the word in a sentence (semantics and congruency - how well word fits in sentence)
spikes negative when less predictable
what is a psychological refractory period? (PRP)
when presenting 2 tasks in rapid succession:
the period of time in which response to second task is affected by the 1st task still being processed
is it possible to precisely pinpoint the regions of the brain where particular EEG/ERP activity originates?
no
how to improve localisation estimates of EEG?
correlate with concurrently acquired fMRI data
what is the ‘inverse problem’ referring to?
inferring cortical generators (region) from known scalp potentials
hard to do
as many cortical current generators that could result in one scalp distribution
severe limitation of EEGs as unable to determine location of electrical activity
what is meant by ‘N1 and P1 components’ regarding EEG wave recordings?
and what is meant by P300?
N means negative
P means positive
1 refers to it being the first peak
P = positive 300 = occurs 300ms after stimulus onset
what is an SOA?
Stimulus-onset asynchrony
amount of time between start of 1st and 2nd stimulus
what does a micro-electrode recording being highly invasive restrict ?
subjects available and brain areas that can be investigated
what happens in the EE frequecies as sleep becomes deeper?
gradual slowing (lower frequency)
pros of EEG over fMRI?
EEG - cheaper and more portable
how are stimuli in ERPs compared?
they are separately averaged
what did Lien et al. find?
processing in task 1 interferes with the processing of the target meaning in task 2
so meaning isn’t accessed automatically
what is a local field potential? (LFP)
temporary deficits or surpluses of electrical charge created outside of a neuron due to transport of ions in and out of neurons
what is meant by scalp distribution in reference to components of ERPs?
map of magnitude of component all across scalp sensors to see where the magnitude of specific component is greatest
so spatial and temporal
what is a ‘component’ of an ERP?
changes in ERP signal resulting in poisitve and negative polarity peaks
what is known as the forward problem?
knowing active set of brain regions and wanting to determine resulting EEG signal on scalp
not too hard
