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Electrophysiology > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

ABR is happening up to about ____ms

A

6 (typically 5.5ms for wave V)

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2
Q

A click ABR typically gives the ____ peaks

A

5

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3
Q

What direction is ABR measured?

A

Positive up

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4
Q

What does the ABR reflect?

A
  • Action potentials (not graded post-synaptic potentials)
  • Requires highly synchronized activity
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5
Q

Do the action potentials line up for ABR?

A
  • Yes
  • The peripheral auditory system is very temporally precise
    -Many neurons fire at precisely the same time to things like stimulus onset
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6
Q

The auditory nerve is about ____ fibers

A

30,000

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7
Q

What is the closed field problem with ABR?

A

Action potentials don’t give rise to open-fields

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8
Q

Where do sinks occur? Where do the sources occur?

A
  • Sinks occur progressively at each break (Node of Ravier) in the myelin sheath
  • Adjacent areas are passive sources
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9
Q

What 2 ways can we break the symmetry to allow for action potentials to give rise to open-fields?

A
  1. Direction change in axon can set up a pseudo-dipole
  2. Change of impedance surrounding axon
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10
Q

Where is the impedance changing?

A

Impedance change between the internal auditory meatus and cranial cavity

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11
Q

The ABR is a ____ response

A

Subcortical

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12
Q

Do subcortical nuclei give rise to open-field

A

No

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13
Q

Do all ABRs look the same?

A

No, we get various morphologies and shapes

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14
Q

Typically, Wave ____ is larger than wave I

A

V

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15
Q

Wave ____ and ____ are often conjoined

A

IV, V

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16
Q

Should you rely on amplitude differences when comparing ABRs?

A

No (amplitudes can be variable)

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17
Q

What waves are horizontal?

A

Waves I, II, and III

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18
Q

What waves are vertical?

A

Waves IV, V

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19
Q

What 3 ways do you find the ABR generators?

A
  1. Correlate with near field activity
  2. Introduce lesion (freezing)
  3. Source localization
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20
Q

What is the most common way to find ABR generators?

A

Correlate with near field activity

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21
Q

Why is it hard to determine the generators for ABR?

A

It happens in the middle of the head in the brainstem

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22
Q

Explain ABR generators and complexity

A
  • Complexity increases as we move up rostrally (up) (multiple simultaneously active pathways)
  • Peaks may have contributions from multiple processes
  • Processes may contribute to multiple peaks
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23
Q

Earlier peaks are ____, later peaks are more ____

A

Simpler, complex

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24
Q

Everything travels along the ____ to get to the brainstem

A

Auditory nerve

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25
Q

What is the speed of the basilar membrane?

A

2.8 m/s or 2.8 mm/ms

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26
Q

How many ms does it take to get from 10kHz to 250Hz?

A

8ms

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27
Q

How many ms does it take to get from 4kHz to 500Hz?

A

4ms

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28
Q

What is the speed of the VIIIth nerve?

A

22 m/s or 22 mm/ms or 2.2 cm/ms

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29
Q

Where do two other delays take place? How long are the delays?

A
  • Cochlear filter build-up time at CF (0.5ms)
  • Synaptic delay (1ms)
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30
Q

What is the length of the VIIIth nerve?

A

2.6cm

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31
Q

How do we localized ABR components?

A

Speed and distances

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32
Q

Is the BM fast or slow?

A

The BM is very slow part of the body (HF at the base, LF at the apex – traveling slow)

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33
Q

High frequencies are at the ____

A

base of the BM

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34
Q

Low frequencies are at the ____

A

apex of the BM

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35
Q

If you play a LF tone and a HF tone at the same time, how much sooner will the BM be stimulated on the HF side (base)?

A

8ms

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36
Q

Each synapse add about ____ms

A

1

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37
Q

How long does it take to get down the VIIIth nerve?

A

A little over 1ms (2.6cm long)

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38
Q

Which wave is the iffiest?

A

Wave IV

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39
Q

What waves are the most reliable?

A

Waves I, II, III, and V

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40
Q

Wave I typically happens at ____ ms

A

1.7

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41
Q

Wave II typically happens at ____ ms

A

2.8

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42
Q

Wave III typically happens at ____ ms

A

3.9

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43
Q

Wave IV typically happens at ____ ms

A

5.1

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44
Q

Wave V typically happens at ____ ms

A

5.7

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45
Q

Do the waves always happen at specific times?
- what does timing vary based on?
- who has an earlier wave V?
- who has a later wave V?

A
  • No, timing varies based on age and sex
  • Wave V is typically earlier in females
  • Someone who is an older male may have a later wave V
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46
Q

Where is wave I generated?

A
  • Wave I arises from the distal (outside) portion of the VIIIth nerve
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47
Q

Latency of wave I is the same as the ____

A
  • Compound action potential (CAP)
  • Wave I is the CAP
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48
Q

Where is wave II generated?

A
  • Wave II arises only from the proximal (inside) end of the 8th nerve (dipoles are oriented away from the mastoid)
  • Occurs about 1 ms after wave I (not long enough to go down AN across synapse to CNS)
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49
Q

Where is wave III generated? Where is it recorded?

A

Cochlear nucleus (recorded from the wall of the 4th ventricle)

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50
Q

Where is wave IV generated? How is it generated?

A

Superior olivary complex (generated contralaterally)

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51
Q

Where is wave V generated? How is it generated?

A

Lateral lemniscus (generated contralaterally)

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52
Q

Why is wave V not generated at the inferior colliculus?

A

Wave V terminates at the inferior colliculus

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53
Q

What does the inferior colliculus generate?

A

SN10 (slow negativity 10) which happens after wave V

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54
Q

How do you get rid of the ABR?

A
  • Damaging the globular and bush cells in the AVCN
  • The AVCN is what gives us sound localization
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55
Q

What frequencies drive the ABR generators?

A

Driven primarily by high frequencies (above 2000Hz)

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56
Q

What 3 ways do you measure the amplitude of ABR?

A
  1. Peak
  2. Peak-to-peak
  3. Interpeak ratio
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57
Q

What 3 ways do you measure the latency of ABR?

A
  1. Absolute
  2. Interpeak
  3. Interaural
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58
Q

Do we rely on amplitude or latency measures more?

A

Latency (when the peak occurs)

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59
Q

What is absolute latency?

A

When a wave occurs based on the stimulus

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60
Q

What is interpeak latency?

A

When did wave x happen according to wave x (the timing difference between two peaks)

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61
Q

What is the best latency measure?

A

Interpeak

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62
Q

Latency measures are more ____

A

Stable

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63
Q

Where do you measure wave I?

A

The center of the peak

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64
Q

Where do you measure wave I if you have two peaks?

A

From the second peak

65
Q

Where do you measure wave II?

A

The center of the peak

66
Q

Where do you measure wave III?

A

From the center, but you often have two little peaks, so look for the mid point (middle)

67
Q

Where do you measure wave IV?

A

The first bump on the IV-V wave

68
Q

Where do you measure wave V?

A

The shoulder of the IV-V wave (the very edge)

69
Q

Standard deviation between absolute latencies is roughly ____ms

A

0.2

70
Q

What waves may have bifid peaks?

A

I and III

71
Q

What 3 ways do you get rid of a bifid wave I?

A
  1. Decrease intensity
  2. Change montage
  3. Pick second peak
72
Q

What do you do with the bifid peak on wave III?

A

find the midpoint

73
Q

How can you separate waves IV and V?

A

Contralateral recording

74
Q

What 4 things are seen in a contralateral recording?

A
  1. IV is .1-.5 ms earlier in contralateral recording
  2. Wave I is absent
  3. II is larger
  4. III is smaller
75
Q

Placing electrodes on each ear gives us a ____ montage

A

Horizontal

76
Q

How do we get a horizontal montage?

A

Can be derived from an ipsi/contra montage

77
Q

How many channels do you need?

A

Two

78
Q

What does a two channel recording give you?

A

Ipsi, contra, and horizontal

79
Q

We are more concerned with the ____ measure

A

Ipsilateral

80
Q

Why might we want a contralateral recording?

A

Cross hearing

81
Q

What kind of response is an ABR?

A

An onset response (transient)

82
Q

What type of stimuli is being used for an ABR?

A

A click (on or off, which is transient)

83
Q

Where does a click have energy?

A

At all frequencies

84
Q

What is a null?

A

The end of a click life

85
Q

We use ____ micro second click because it gives us a null at ____ Hz

A

100, 10,000

86
Q

Where is the peak energy in an ABR? Why?

A

3 kHz (because of the filtering properties of the ear)

87
Q

What happens to an ABR if the individual has hearing loss?

A

The ABR will shift because it starts from a different spot on the cochlea

88
Q

What is a different stimuli that can be used for ABR?

A

A tone burst

89
Q

How does an ABR work with tone burts?
- compare to a click
- what does it give rise to
- what type of tone burst is often used

A
  • A tone burst is more frequency specific than a click
  • A tone burst is short and gives rise to synchronized activity
  • Often use tones that are 5 cycles
    • With a 1K tone, one cycle is 1 ms (5 cycles is 5ms)
    • A 500Hz tone, one cycle is 2ms (5 cycles is 10ms)
    • A 2k tone, one cycle is 0.5ms
90
Q

What does windowing improve?

A

Windowing can improve place specificity (how fast it is turned off and on)

91
Q

What are the 4 different types of windowing?

A
  1. Trapezoid
  2. Triangular
  3. Cosine squared
  4. Blackman
92
Q

What is the most common type of windowing?

A

Blackman (has a more narrow peak)

93
Q

What are the 2 types of stimulus polarity?

A
  1. Rarefaction (going away from the ear)
    • negative pulse
    • depolarizing
  2. Condensation (going towards the ear)
    • positive pulse
    • hyperpolarizing
94
Q

____ gives you the first peak

A

Rarefaction

95
Q

____ peaks are happening slightly earlier than ____ peaks

A

Rarefaction, condensation

96
Q

What polarity is often used in ABR?

A

Alternating polarity

97
Q

What is alternating polarity?

A

Combine rarefaction and condensation

98
Q

What is the problem with alternating polarity?

A
  • They do not overlap perfectly (therefore alternating polarity gives you an ABR that is not quite as clear)
99
Q

Why do we do alternating polarity for ABR?

A
  • Stimulus-related electrical artefact
  • Cochlear microphonic (inverts with the stimulus)
100
Q

Amplitude of the ____ is proportional to the reciprocal of the square root of the number of trials

A

Noise

101
Q

Noise amplitude is 2x as low with ____x number of trials

A

4

102
Q

noise amplitude is 4x as low with ____x number of trials

A

16

103
Q

noise amplitude is 8x as low with ____x number of trials

A

64

104
Q

The more trials, the lower the ____

A

Noise

105
Q

What should we do to remove 60Hz?

A

Use a stimulus rate that will put 60 Hz 180° out of phase on every other trial

106
Q

60 Hz period is ____ms

A

1000/60 = 16.666ms

107
Q

What is the half period of line noise?

A

8.3333 ms

108
Q

If we want a trial to be in the opposite phase of 60Hz what do we do?

A
  • 60Hz period is 16.666ms
  • Half of this is 8.333 ms (120 Hz)
  • Want something that is an odd integer multiple (1, 3, 5, 7, 9) of the half period of line noise (8.3)
109
Q

Is 30Hz a good stimulus rate?

A
  • 1000/30 = 33.333 ms
  • 33.333/8.3 = 4 times the 1/2 period of line noise
  • Not good because not an odd integer multiple
110
Q

Is 40Hz a good stimulus rate?

A
  • 1000/40 = 25 ms
  • 25/8.3 = 3 times the 1/2 period of line noise
  • This is a great stimulus rate!
111
Q

What are 3 good stimulus rates?

A

17.14, 13.33, 10.91 Hz

112
Q

Explain non-coherent averaging (induced)

A
  • Figure out the frequencies that are present than average those freqeucnies
  • The advantage to this is that time differences don’t matter (lets us look at induced activity in the brain)
  • Shows non time-locked frequencies in the brain
  • Induced activity is not looked at clinically
113
Q

What are 4 subjective methods for detecting responses?

A
  1. Subjective detection by single person
  2. Subjective detection by multiple people
  3. Response replication
  4. Response tracking
114
Q

How many tracings do you need to do for ABR?

A

two

115
Q

T/F: the waves have to be repeated to be marked

A

True

116
Q

What do you do if you can only get one tracing?

A

Divide it in two

117
Q

How does visual inspection and replication work?

A
  • Two runs of 2500 sweeps
  • They don’t overlap very well (can only see wave V)
  • Looking to see if any waves repeat/overlap
118
Q

How does response tracking work?

A

Adjusting the level of an ABR is one of the fastest things you can do (the higher the level the easier to see the distinct waves)

119
Q

What frequency do we typically high-pass for threshold?

A

30Hz

120
Q

What frequency do we typically high-pass for diagnostic?

A

100Hz

121
Q

How we ____ changes the amplitude

A

Filter

122
Q

What does high pass filtering do?

A

Gets rid of LF energy, line noise, things we don’t want, noise

123
Q

What does low pass filtering do?

A

Prevents aliasing

124
Q

What is the narrowest frequency range of ABR?

A

150-1500Hz

125
Q

What is the typical range for the low-pass filter?

A

1500-3000Hz

126
Q

A high-pass filter of ____Hz is good for showing wave V

A

30Hz

127
Q

A high-pass filter of ____Hz is good for showing waves I and III

A

150Hz

128
Q

Wave amplitude changes as a function of ____ filtering

A

High-pass

129
Q

What do you need to do before using a sound level meter?

A

Make sure it is measuring correctly

130
Q

What level should almost all SLMs present?

A

94dB (1 volt)

131
Q

SLM fast integration ____ of a second

A

1/8th

132
Q

How does calibrating the stimuli work?

A
  • Create tone that is the level you want (in dB SPL), usually with an audiometer!
    • e.g., 80 dB SPL
    • use SLM to verify
  • Measure this on an oscilloscope
  • Create a click or tone-burst that matches the range on the oscilloscope
133
Q

What is 0 dB HL?

A

0 dB HL is average behavioral threshold for pure tone

134
Q

What is 0 dB nHL?

A

0 dB nHL is average behavioral threshold for click

135
Q

We need to convert ____ to ____ for ABR

A

HL, nHL

136
Q

Recording parameters: rate? polarity?

A
  • Rate: 39.1/s
  • Polarity: alternating
137
Q

Explain the latency-intensity function

A
  • About 40 µs per dB, OR
  • about 400 µs (0.4 ms) per 10 dB
138
Q

Explain the latency-intensity function graph (clicks)

A
  • At a low level, latency to wave V is much longer
    • 20dB, 8.25ms
  • At a high level, latency to wave V is much quicker
    • 80dB, 5.5ms
139
Q

What is the only wave you get at soft levels?

A

Wave V

140
Q

L-I function for tone bursts

A
  • LF (500Hz), wave V latency = 15ms
  • HF (8000Hz), wave V latency = 9ms
141
Q

Why are functions steeper for low frequencies?

A
  • The delay of the cochlea (the traveling wave)
  • This is why 500Hz is so much longer than 8000Hz (this is at low levels)
  • At high levels, there isn’t as much cochlear delay because more of the BM is activated
142
Q

Wave ____ is less delayed than earlier peaks, as level is decreased

A

V

143
Q

Since early waves are more delayed at low levels, ____ latency is smaller at low levels

A

I-V

144
Q

Do stimulus rate and response latency affect wave I?

A

For wave I, latency is not (or barely) affected by stimulus rate

145
Q

Are waves II-V affected by stimulus rate and response latency?

A
  • Waves II-V
    • Latency increases, amplitude still decreases
    • Rate-related delay is synaptic delay—increases with number of synapses
  • Wave V latency most affected
146
Q

Do stimulus intensity/rate and response amplitude affect wave I?

A

Wave I amplitude is very affected by intensity and rate

147
Q

Do stimulus intensity/rate and response amplitude affect wave V?

A
  • Wave V amplitude is least affected by intensity and rate
  • Threshold applications use higher rate (ca. 40/s)
  • Neurodiagnostic applications use lower rate (ca. 10-20/s)
148
Q

Wave V is very ____

A

Robust (can be recorded in the worst conditions)
- Can go fast and slow

149
Q

Wave I is very ____

A

Delicate
- Needs to be slow and high

150
Q

What 2 things are unique about wave V?

A
  • Wave V becomes later at high rates—latency is more affected by stimulus rate than earlier waves
  • BUT! wave V amplitude is least affected by stimulus rate
  • We can record a large wave V at high rates, but it occurs later!
151
Q

Noise decreases ____ and increases ____

A

Amplitude, latency

152
Q

Wave V amplitude fairly resilient to rate, but not to ____

A

Noise

153
Q

Wave V latency similarly affected by ____ and ____

A

Noise, rate

154
Q

Recording parameters - electrodes

A
  • Cz / Fpz to M1/M2 (A1/A2)
    • M = mastoid, A = auricle
155
Q

Recording parameters - filter

A
  • 30/100 Hz –> 1500/3000 Hz
    • 100Hz is for diagnostic ABR (wave I and III)
    • 30Hz is for thresholds (wave V)
156
Q

Recording parameters - averaging

A

1000-2000 (2000 most often)

157
Q

Recording parameters - rate

A
  • 10.1-39.1/s
  • Slow rate is typically for neurodiagnostic
  • Thresholds typically use a high rate and a low filter
158
Q

Recording parameters - stimulus

A
  • 100 µs click / 2-1-2 tone-burst
  • Often blackmen window
159
Q

Recording parameters - rejection

A

+/- 25 uV

Electrophysiology (8 decks)

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