Introduction to EEG

Question 1

Who invented the EEG? Which type of wave was first recorded and when?

Answer 1

Hans Berger. Alpha waves were first recorded in 1929

Question 2

What is usually the measuremement of EEG signals? Do they need amplification?

Answer 2

𝜇V range usually, they need to be amplified

Question 3

What is the orientation of pyramidal neurons relative to the cortex surface and to each other?

Answer 3

Pyramidal neurons in the 5th and 6th layer are parallel to each other and perpendicular to the cortex surface

Question 4

What is the orientation of the dipole crated by Post Synatic Potential in apical dendrites?

Answer 4

Towards the soma of the cell

Question 5

WHat does then the EEG measure current wise?

Answer 5

Modulation in EXTERNAL (to the neuron) currents. Are there specific types of neurons that are more responsible for it?

Question 6

How do these cells need to be oriented and usually which type are they?

Answer 6

They need to be close and parallel and firing in synchrony. (I think also cells in deep sulci are more difficult to record with accuracy).
Exactly, cells in gyri are more strongly recorded

Question 7

What happens when there is excitatory input to layer 5 and 6 pyramidal cells soma? WHich cells usually cause it?

Answer 7

There are positive EEG deflections, (usually it is input from thalamic cells??)

Question 8

What happens when there is excitatory input to layer 5 and 6 pyramidal cells apical dendrites? WHich cells usually cause it?

Answer 8

Negative EEG deflections, (usually caused by input from contralateral cortex via corpus callosum??)

Question 9

How does synchrony affect the amplitude of the EEG signal?

Answer 9

More sinchrony –> Bigger amplitude of signal

Question 10

10-20 system, why is it adopted? What are nasion and pinion?

Answer 10

To have a universal standard across different subjects and labs, nasion and inion are reference points for placement of electrodes

Question 11

In which areas is the scalp divided in the 10-20 system?

Answer 11

Brain lobes: Frontal, Parietal, Temporal, Occipital.
Further anatomical landmark: Central sulcus

Question 12

What are possible causes of artfacts in EEG?

Answer 12

Ocular causes: blink, saccades,
Muscle artifacts: Muscle twitching, clenching of teeth, talking, heartbeat
Sweat artifacts: slow drift

Question 13

What does a low pass filter remove?
What about a high pass?

Answer 13

A low pass filter (40Hz) removes EMG activity
A high pass filter (0.01 Hz) removes slow drifts

Question 14

What are the differences between spontaneous oscillation and event related potentials?

Answer 14

Spontaneous oscillation: They are rythm of the brain, they vary between types of states in the brain, defined by frequency bands.
ERP: Time locked to a specific outside event.
Short duration (100-700 ms). Modulated by many factors

Question 15

Are ERP tied to external or internal events?

Answer 15

Both

Question 16

How is the signal to noise ratio in EEG? Is it just due to artifacts?

Answer 16

Bad, no it is due to the fact that usually ERP are investigated but the brain is producing lots of background activity which is just noise for the purpose of the research.

Question 17

What is the most common approach to separate noise from signal of ERP related activity?

Answer 17

Doing lots of trial and averaging across them afterwards.

Question 18

Mathematical modeling of EEG, how are the two components (ERP and noise) mathematically modelled?

Answer 18

ERP p(t) is assumed to be constant in each trial while noise, “residual” is iid 𝒩 (0, 𝜎2
𝑟) distributed.
Let us assume the ERP 𝑝(𝑡) is constant in each trial 𝑘 (𝑘 = 1, . . . , 𝐾),
while the ‘residual’ 𝑟𝑘(𝑡) is iid 𝒩 (0, 𝜎2
𝑟
) distributed:
𝑥𝑘(𝑡) = 𝑝(𝑡) + 𝑟𝑘(𝑡) for 𝑘 = 1, . . . , 𝐾
Then averaging across trials lead to
signal being speared from sommatoria e media del rumore (?) The amplitude of the noise goes down by a factor of √𝐾 in an
average across 𝐾 trials.

Question 19

What does P and N stand for when characterizing ERP? e.g (P300, N170..)

Answer 19

Positive or negative polarity of the deflection (check what it specifically means in this context)

Question 20

Function releated names for ERP, e.g. LRP,Pe,Ne

Answer 20

Lateralized Readiness Potential,
Positive Deflection related to erroneous decisions
Negative Deflection related to erroneous decisions

Question 21

What are the characteristics of early components?

Answer 21

Usually endogenous, arising soon after stimulus, can be used to test normal connectivity of sensory pathways, can be modulated by mood or attention, reward etc.

Question 22

What are the characteristics of later components?

Answer 22

reflect internal, higher-order processing
not strongly dependent of physical stimulus properties
influenced by task, strategy, emotional processing, etc

Question 23

Early components, P1

Answer 23

Occipitally located, peaks 100 ms after visual stimulus. Attention allocation amplifies the stimulus

Question 24

Late components, P3

Answer 24

▶ Typically observed in the oddball paradigm
▶ Infrequent target (T) stimuli are randomly presented in a background
of frequent standard (S) stimuli
▶ Subjects are instructed to respond mentally or physically to the
targets, and not respond otherwise

Question 25

How is the power spectrum of EEG? Which frequency bands do not follow the rule?

Answer 25

The power spectrum of EEG typically follows the 1/𝑓 law
▶ However, there exist certain “brain rhythms”, which are characterized
by slightly higher power in particular frequency bands, brain frequencies, gamma beta alpha theta delta