6) Methods 2 (EEG + ERPs)

Question 1

How are EEGs and ERPs different to TMS?

Answer 1

They have equally good temporal resolution but they have coarser spatial resolution

Question 2

What is the biophysical basis of EEGs?

Answer 2

When under the influence of postsynaptic potentials, cortical neurons create surface-negative electrical dipoles

Question 3

What 2 factors of neurons affect the signal strength?

Answer 3

-Neuron alignment
-Synchronous firing

Question 4

How does neuron alignment affect signal strength?

Answer 4

Many neurons are aligned perpendicular to the cortical surface, with dendrites closer to the surface and axons closer to the white matter.
-As the dendrites are parallel to each other, the dipoles in individual cells add up to a stronger signal

Question 5

How does Synchronous firing affect signal strength?

Answer 5

Enhances the signal and allows it to be recordable non-invasively as electrodes can be placed on the scalp

Question 6

In an EEG, what does the distance between two vertical lines correspond to?

Answer 6

1 second

Question 7

What is an alpha rhythm?

Answer 7

An occipital rhythm of 10 cycles per second/ 10 Hertz

Question 8

How is an alpha rhythm typically blocked?

Answer 8

Opening the eyes

Question 9

What are the cyclic changes in amplitude referred to as?

Answer 9

Oscillations

Question 10

What happens in bets, 13-30Hz ?

Answer 10

Most evident frontally, dominant rhythm when subject is alert, eyes open

Question 11

What happens in alpha, 7-13Hz ?

Answer 11

Occipital maximum, dominant when subject is relaxed with eyes closed, blocked by opening the eyes (“Berger effect”)

Question 12

What happens in theta, 3-7Hz ?

Answer 12

Slow activity, rare in adults when awake but perfectly normal in children (up to ~13 years) and sleep

Question 13

What happens in delta, <3Hz ?

Answer 13

Dominant rhythm in infants (up to ~ 1 year) and stages 3 and 4 of sleep

Question 14

What are the 2 EEG based parameters for bio psych?

Answer 14

Event-related oscillations
Event related potentials

Question 15

What are Event related oscillations?

Answer 15

stimulus or task-related changes in EEG oscillations, in terms of frequency or amplitude
Temporal resolution 10s-100s ms

Question 16

What are event related potentials?

Answer 16

Waveforms defined in terms of latency relative to an event such as a sensory stimulus and obtained through time-locked averaging of EEG
Temporal resolution 10s of milliseconds

Question 17

ERPs are recorded as averaged EEGs in which 2 ways?

Answer 17

-Record EEG trials that are time-locked to the event of interest
-Each trial contains an ERP and voltage fluctuations that are not time-locked

Question 18

Which 2 aspects have to be excluded from averaging?

Answer 18

-Movement of the eyeballs
-Muscle activity

Question 19

What are the 2 ways to classify ERPs?

Answer 19

-Exogenous
-Endogenous

Question 20

What are Exogenous ERPs?

Answer 20

Automatic response of the brain controlled by physical properties of stimulus

Question 21

How are Exogenous ERPs elicited?

Answer 21

Whenever the modality-specific sensory pathway is intact

Question 22

How are Exogenous ERPs influenced?

Answer 22

By intensity/frequency of stimuli

Question 23

What are Endogenous ERPs?

Answer 23

Reflect the interaction between the subject and event eg cognitive processes such as attention

Question 24

What are most ERPs actually?

Answer 24

Neither strictly exogenous nor strictly endogenous.
They are rather semi-automatic but modulated by cognitive processes (mesogenous)

Question 25

What does N1-P2 depend on for 'mesogenous' ERPs?

Answer 25

-Stimulus intensity -Stimulus presentation

Question 26

What does Topography depend on for EEGs and ERPs?

Answer 26

A site of reference electrodes

Question 27

How does topography highlight a difficulty in using ERPs?

Answer 27

For localisation of neural sources as the topography for one areas cannot be distinguished from another

Question 28

What is another potential difficulty of using ERPs and how can it be overcome?

Answer 28

-The scalp distorting the electrical field Overcome by recording magnetic instead of electrical fields as the skull is transparent to magnetic fields

Question 29

What is the a mismatch negativity in ERPs?

Answer 29

Elicited by an infrequent deviant stimulus in a sequence of frequent standard stimuli.

Question 30

What happens when the stimuli is more different?

Answer 30

The shorter the Mismatch negativity latency and the larger the mismatch negativity amplitude

Question 31

What 2 underlying processes does the mismatch negativity reflect?

Answer 31

-Preattentive processing of deviant features -Sensory memory or 'echoic memory'

Question 32

What is the 'novelty' P3/P3a a response to?

Answer 32

An unexpected deviant stimuli with an amplitude maximum over frontal electrodes

Question 33

When is the Omitted stimulus P3 observed?

Answer 33

When expected stimuli do not occur

Question 34

How can the signal underlying EEG be measured?

Answer 34

Using magnetoencephalography (MEG)

Question 35

What is Magnetoencephalography?

Answer 35

Electrical activity in the brain generates magnetic fields which can be measured outside the head

Question 36

How does the skull being 'transparent' improve the MEG sensors?

Answer 36

Better spatial resolution than in EEG/ERP

Question 37

What are MEGs sensitive to?

Answer 37

Highly sensitive to electromagnetic noise and therefore requires magnetic shielding.

Question 38

What do EEGs measure? What is the temporal and spatial resolution quality?

Answer 38

Synchronous activity of large neural populations -Excellent temporal resolution -Poor spatial resolution

Question 39

What do exogenous vs endogenous ERPs waveforms depend on?

Answer 39

Stimulus properties Interaction between subject and event

Question 40

How are ERPs obtained?

Answer 40

Through time-locked averaging to improve signal to noise ratio