Electrophysiology

Question 0

Artifact Rejection Level

Answer 0

The level of artifact allowed, (<10%), so that all stimulus is accepted and spurious activity is rejected.

Stimulus within artifact criterion = good sweep
Stimulus exceeds rejection threshold = rejected sweep

Question 1

Exogenous vs. Endogenous

Answer 1

Exogenous: Sensitive to stimulus manipulation

Endogenous: Sensitive to psychological state of subject

Question 2

N400

Answer 2

A measure of semantic incongruities e.g. I have my tea with milk and poop

Latency: 400ms

Question 3

What is the relationship between audiometric thresholds and ABR

Answer 3

In general there is a good correspondence between audiometric threshold and ABR threshold. (match well for high frequency, 500 Hz threshold on ABR is usually worse than audio)

In the presence of a retro-cochlear/neurologic disorders ABR thresholds and PTA do not show a correspondence

Question 4

Stimulus delivery

Answer 4

Stimulus generation
D/A conversion 
Trigger response in ear 
Pre-amplification 
Amplification 
Filtering 
A/D conversion 
Averaging

Question 5

Cochlear Microphonic

Answer 5

It is an alternating current (AC) receptor potential elicited by sound.

It reflects the instantaneous motion of the cochlear partition in the vicinity of the recording electrode

It reflects the spatial average of the extracellular correlate of the inner (IHC) and outer hair cell (OHC) receptor currents.

Currents have 3 properties when recorded form outside the Cochlear :

1) Dominated by the more populous OHC.
2) Dominated by hair cells located at the base of the cochlear irrespective of stimulus frequency.
3) They reflect both the displacement and the velocity of the cochlear partition.
a) OHCs and displacement of the cochlear partition thought to contribute to the CM at low stimulus intensities
b) IHCs and velocity of the cochlear partition thought to contribute to the CM at higher stimulus intensities

Question 6

Stimulus polarity

Answer 6

Condensation: Headphone diaphragm displaced outwardly; TM displaced medially

Rarefaction: Headphone diaphragm displaced inwardly; TM displaced laterally

Question 7

Sampling rate

Answer 7

The number of samples played per second

Increasing sample rate = Increase in wave V latency.

Latencies of earlier components of the ABR are generally unaffected = Increase in inter-wave latency interval

Amplitude of the earlier ABR waves decreases with increasing rate

Question 8

Impedance

Answer 8

Resistance, opposition to current flow.

It is important to have low and balanced impedance across electrodes

Question 9

Filtering - effects on waveform

Answer 9

High-pass filter: As the low frequency cut-off increases (narrowing of filter) - ABR amplitude, especially for wave V decreases and latency progressively decreases.

Question 10

P300

Answer 10

A cochlear potential.
It is sensitive to attention and cognition
Elicited by MMN

Question 11

Trigger

Answer 11

The response sent to the computer recording the responses so it knows when the stimulus is started

Question 12

Rate of maturation

Answer 12

Latency decreases with maturation

Myelination

Question 13

Susceptibility to state changes

Answer 13

The shorter the latency the less susceptible to changes in subject state

ABR is not susceptible to state
Cortical is susceptible to state

Question 14

Electrode position

Answer 14

The shorter the latency the more far field the response

Question 15

Variability

Answer 15

The shorter the latency the smaller the variability

Question 16

Stimulation rate

Answer 16

The shorter the latency the faster the rate

Question 17

Spectrum

Answer 17

The shorter the latency the higher the frequency spectrum

ABR: 30 - 1500 Hz
MLR: 10 - 100 Hz
Late potentials: 0.1 - 30 Hz
EEG: 1-12 Hz

Question 18

Amplitude

Answer 18

The shorter the latency the smaller the amplitude

Subcortical: < 10μN
Cortical: >10μN

Question 19

Latency

Answer 19

Absolute latency: the time between a peak and the stimulus onset

Inter-peak latency: the time between two peaks in an ABR wage form

Question 20

Trigger

Answer 20

The beginning of the time window. This signals the averager that the stimulus has been sent

Question 21

Pre-stimulus interval

Answer 21

Period between trigger and stimulus

Enables assessment of non-stimulus related brain activity

Question 22

ISI - inter-stimulus interval

Answer 22

Time from the offset of one stimulus to onset of the next

SOA - Duration

Question 23

SOA - Stimulus onset asynchrony

Answer 23

Time from onset of one stimulus to onset of the next

1/Rate & ISI + Duration

Question 24

Condensation

Answer 24

Headphone diaphragm is displaced outwardly; TM displaced medically

Produces slightly longer latencies. Wave V amplitude tends to be longer

Question 25

Rarefaction

Answer 25

Headphone diaphragm is displaced inwardly; TM is displaced laterally

Produces slightly shorter latencies with higher amplitude for the early components of ABR