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
Frequency band: Delta
<4Hz
- sleep
- some attention tasks
Frequency band: Theta
4-7Hz
Is similar to Alpha:
- resting, tiredness, attentional lapses
Frequency band: Alpha
7-14Hz
- resting
- tiredness
- attentional lapses
Frequency band: Beta
15-30Hz
- motor behaviour
- concentration
Frequency band: Gamma
> 30Hz
- long range neural synchronization
What technique can be used to make the brain oscillate at a particular frequency?
Steady state
- presenting a stimulus oscillating at a desired frequency (sound, image, somatosensory)
Where is the steady state EEG approach useful?
Working with children or animals (no communication required)
What do head and contour plots show
typically the distribution of activity across electrodes at a SPECIFIC point in time
(heat maps for a given time)
ERP: A basic visual response
P100 (occipital)
ERP: A basic auditory response
N100 (frontal)
ERP: Produced by face stimuli
N170
ERP: Reflects decision making
P300
ERP: An indicator of motor planning
Lateralized readiness potential (LRP)
Where in clinical research is EEG used?
- Epilepsy
- Migraine
- Movement disorders (e.g. Parkinson’s)
- Psychiatric disorders
- Diagnosing brain death, coma etc.
How is EEG used in sleep research?
Different stages of sleep are associated with characteristic patterns of EEG activity
- EEG can be used to investigate sleep disorders, and study consolidation of learning during sleep
How is EEG used in basic sensory research?
- Assessing hearing deficits, the efficacy of cochlear implants
- Vision: steady-state EEG has become more popular
The advantage of basic sensory research is that it can be used on subjects who cannot respond to a behavioural task (e.g. very young children)
EEG has excellent ____ resolution but poor ____ resolution
temporal, spatial
fMRI has excellent ____ resolution but poor ____ resolution
spatial, temporal
To use EEG with fMRI you need an MR-compatible EEG system…
without too much metal
(EEG & MEG together) Because the magnetic field and electrical dipole are _____, measuring both simultaneously can…
- orthogonal
- aid enormously in source localization
What are the advantages of EEG?
+ Cheap (consumables cost
What are the future uses of EEG?
- Human-computer interaction
- Gaming headsets
- BCI/neurofeedback
