5. EEG Flashcards
Who invented EEG?
Hans Berger
(EEG) opposite potentials in a sulcus can…
cancel each other out
In EEG we are measuring…
a difference in electrical charge (this is called voltage)
(EEG) voltages are ____ measures across the head
relative
- there must always be a reference electrode
a microvlot is ____ of a volt
a millionth
The voltages we measure with EEG are ___, typically in the order of tens of ____
voltages, tiny, microvolts
What is the nasion?
EEG cap placement reference point:
- just above the bridge of the nose (between eyes)
- From the Cz electrode to the Nasion should be 50% of the distance of the semicircle
What is the inion?
EEG cap placement reference point:
- The bump at the base of the skull
- From the Cz electrode to the inion should be 50% of the distance of the semicircle
impedance is measured in…
ohms (Ω)
How can impedance be reduced?
By using conductive gel or paste
what is impedance?
- a measure of the overall opposition of a circuit to current
- It is like resistance, but it also has a phase component
___ impedances are considered good
<5kΩ
(EEG) any noise introduced before the amplifier…
will be amplified too
Applying a ____ can sometimes make the EEG waveforms easier to interpret
smoothing filter (e.g. low pass filter)
What are some of the methods used to precisely record on the EEG trace when a stimulus was shown
- triggers based on sound/light signals
- using digital connections between computers
In many experimental paradigms, one computer records the EEG while a different computer…
displays some stimuli
(EEG) the true signal we are interested in can be revealed by…
averaging over multiple trials and/or multiple subjects
- we might also avg over several electrodes to get a global signal for a particular region
EEG artifact removal:
Various labs use different rejection criteria:
- e.g. removing trials where some measure exceeded ____ of the mean
±3SE
What is independent components analysis (ICA)?
Independent component analysis attempts to decompose a multivariate signal into independent non-Gaussian signals.
- A simple application of ICA is the “cocktail party problem”, where the underlying speech signals are separated from a sample data consisting of people talking simultaneously in a room
What is an ERP
Event related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event
negative voltages are plotted ____ in ERP
upwards
What is used to quantify ERPs?
- Peak amplitude and/or latency
- or the area under deflection (peak)
What is the Fourier analysis technique?
Any waveform can be broken down into or deconstructed from the sum of sine waves of different frequencies
- A convenient representation of this is to plot the amplitude (or power) as a function of frequency (y = amp / x = freq)
(EEG) ____ plots represent how the Fourier spectrum changes over time
Frequency vs time plots:
y = freq / x = time
