Week 2: Overview of AEPs

Question 1

basic principle of averaging AEPs

Answer 1

superimpose tracings from several repetitions to discover common features vs noise (facilitates extraction of the signal)

Question 2

what are the 4 functions of the preamplifier

Answer 2

• differential amplification
• amplification
• artifact/noise rejection
• source loading (electrode-scalp)

Question 3

how does differential amplification work?

Answer 3

EEG activity/noise is similar at both electrodes and is thus cancelled out when the response from one electrode is flipped (this helps the small AEP to be detected)

AKA common mode rejection

Question 4

how does amplification work?

Answer 4

examiner sets an amount of amplification to be applied to incoming electric signal in units of gain or sensitivity

Question 5

how does artifact/noise rejection work?

Answer 5

rejects incoming samples of data if they exceed an amplitude thresholds you set

Question 6

three ways artifact noise rejection is done (all work together)

Answer 6

• differential amplification
• common mode rejection ratio
• –a meaure of the preamplifier’s ability to reject similar (common) activity at non-inverting and inverting electrodes
• electrode placement (source loading)

Question 7

source loading

Answer 7

• scalp electrode is a voltage source with a relatively high Z which makes it a weak source
• –it cannot supply significant current to flow from the voltage source to the instrument
• **Z is electrical impedance!
• the pre-amplifier therefore must have a very high input Z

Question 8

the 4 types of AEPs by latency

Answer 8

• early potentials
• middle potentials
• late potentials
• auditory steady state response

Question 9

2 examples of early potentials

Answer 9

• ecochg

* ABR

Question 10

1 example middle potential

Answer 10

middle latency response

Question 11

1 example late potential

Answer 11

late latency response

Question 12

2 examples auditory steady state response

Answer 12

• 40 Hz ASSR

* high modulation rate ASSR (>/= 70HZ)

Question 13

Exogenous EPs

Answer 13

• stimulus or signal related potentials

- –determined largely by stimulus parameters

Question 14

endogenous EPs

Answer 14

• event related potentials evoked by the circumstances of the stimulus events
• –by the relative novelty of one vs the other (odd-ball)
• –have longer latency due to cortical processing

Question 15

parameters that must be decided when recording an AEP that will have an effect on the waveform

Answer 15

• equipment variables
• –size of analysis window
• –width of the filter bandpass
• signal variables
• –spectrum of the signal (click, toneburst)
• –presentation rate
• subject variables
• –age, gender, normal vs pathologic
• –subject state (awake or sleep, and attention)
• circumstances under which the AEP is elicited (oddball paradigm)

Question 16

5 clinical applications of AEPs

Answer 16

1) predict hearing sensitivity (esp in kids and non-organic HL)
3) neonatal hearing screenings
3) otoneurologic Dx (tumors, ANSD, menieres, APD)
4) intraoperative monitoring
5) cochlear synaptopathy