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Electrophysiology > Lecture 3 + 4 > Flashcards

Lecture 3 + 4 Flashcards

1
Q

How many peaks does an ABR have?

A

5

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2
Q

T/F: The ABR reflects actions potentials, NOT post-synaptic graded potentials

A

TRUE

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3
Q

T/F: the peripheral auditory system has poor temporal resolution

A

FALSE: it is very temporally precise. Many neurons fire precisely at the same time to things like stimulus onset. Rapid onsets and changes tend to be important for this

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4
Q

Sinks or sources occur progressively in the extracellular space at each node of Ranvier?

A

Sinks

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5
Q

ABR occurs up to how many ms?

A

6 ms (typically 5.5 ms for wave V)

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6
Q

What direction is ABR measured?

A

Positive up (but used to be negative up)

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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

Why is “breaking the symmetry” helpful in ABR?

A

Changes in direction or impedance will break the symmetry and allow for open fields (which is important for action potentials to synchronize)

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9
Q

Do all ABRs look the same?

A

No, there is a lot of individual variation in morphology

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10
Q

Typically, wave ___ is larger than wave I

A

V

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11
Q

Waves __ and __ are often combined

A

IV and V

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12
Q

What ABR waves are horizontal?

A

I, II and III

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13
Q

Which ABR waves are more vertical?

A

IV and V

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14
Q

What 3 ways can we find ABR generators?

A
  1. Correlate with near field activity
  2. Introduce lesion (e.g., freezing)
  3. Source localization
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15
Q

Explain ABR generators and complexity

A

-Complexity increases as we move rostrally (up)
·Multiple simultaneously-active pathways (parallel processing)

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16
Q

Speed of the basilar membrane

A

2.8 m/s (or 2.8 mm/ms)

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17
Q

Speed of VIIIth nerve

A

22 mm/ms (2.2 cm/ms)

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18
Q

Cochlear filter build-up time (at CF)

A

0.5 ms

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19
Q

Synaptic delay

A

1 ms

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20
Q

Length of VIIIth nerve

A

2.6 cm

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21
Q

Where does Wave I occur?

A

1.7 ms

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22
Q

Where does Wave II occur?

A

2.8 ms

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23
Q

Where does Wave III occur?

A

3.9 ms

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24
Q

Where does Wave IV occur?

A

~5.1 ms

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25
Q

Where does Wave V occur?

A

5.7 ms

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26
Q

T/F: Wave V occurs earlier in biological females compared to biological males

A

TRUE

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27
Q

Which frequencies contribute most to the ABR? (High, low or mid)

A

High

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28
Q

Where does Wave I arise from?

A

-The distal portion of the 8th nerve
-Latency is the same as the CAP (~1.5-1.7 ms); Wave I IS the CAP (negative at mastoid)

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29
Q

Where does Wave II arise from?

A

-The proximal (inside) end of the 8th nerve
-Dipoles are oriented away from mastoid (mastoid negative)

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30
Q

Where does Wave III arise from?

A

-Cochlear nucleus is the main source; also proximal portion of AN
-Mostly horizontal dipole (mastoid negative)

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31
Q

Where does Wave IV arise from?

A

-Likely the superior olivary complex (and elsewhere)
-Mostly vertical dipole moving toward vertex (mastoid negative)

32
Q

T/F: Wave IV is generated ipsilaterally

A

FALSE: Wave IV is generated contralaterally

33
Q

Where does Wave V arise from?

A

-Likely the lateral lemniscus (NOT generated by the IC)
-Mostly vertical dipole moving toward vertex (mastoid negative)

34
Q

Studies on investigating ABR generators in cats revealed which two main cells as being involved? What frequencies are they primarily driven by?

A

Globular and bushy cells; 2000 Hz and above (high frequencies)

35
Q

What are the two categories used to measure ABR and what are they composed of?

A
  1. Amplitude measures: peak, peak-to-peak, and interpeak ratio
    ·Usually use peak-to-peak
  2. Latency measures: absolute, interpeak, interaural
    ·Interpeak is the best latency measure
36
Q

Which waves are measured from the center of the peak and which are measured from the shoulder?

A

-Waves I-III are measured in the center
·Measure the second peak in wave I if there are two peaks cause it’s more reliable
·Measure from the midpoint of wave III if there are two peaks
-Wave V is measured on the shoulder/edge (right past the peak)

37
Q

Why is contralateral recording useful in ABR?

A

Because in ipsilateral recording, waves IV and V are often fused. In contralateral recording, they become easier to distinguish

38
Q

Recording the ipsi and contra on ABR and will give rise to how many channel recordings?

A

3: ipsi, contra and horizontal (horizontal not very useful though)

39
Q

ABR is a ___ response, reflects ___ and requires ___ activity

A

Onset, action potentials, highly synchronized

40
Q

What frequency contains the peak amplitude for ABR using clicks?

A

3 kHz

41
Q

If the peak amplitude occurs at 3 kHz, what happens at lower frequencies?

A

The peaks arrive later (happens to all 5 waves)

42
Q

Why are tone bursts (5-10 Hz) used over clicks in ABR?

A

They are still fast enough to get a good signal for the ABR, but are more frequency/place specific than a click

43
Q

What is windowing?

A

How fast we turn the sound on and off

44
Q

What is the most popular window for ABR and why?

A

Blackman is the most popular because it’s a nice shape and has a more narrow peak

45
Q

What are the two types of stimulus polarities?

A

-Rarefaction waves: negative electrical pulse, pushing the eardrum out (sound goes away from ear)
-Condensation waves: positive electrical pulse, pushing the eardrum in (sound is pushed into the ear)

46
Q

T/F: condensation causes depolarization of the hair cells

A

FALSE: rarefaction is the stimulating phase and causes depolarization. Condensation causes hyperpolarization

47
Q

Do rarefaction or condensation wave peaks occur earlier?

A

Rarefaction peaks occur a little earlier

48
Q

What is the benefit of alternating polarity when doing ABRs?

A

It eliminates stimulus-related electrical artefact and cochlear microphonic (but gives a slight decrease in quality)

49
Q

How does amplitude of the noise relate to the number of trials in an ABR?

A

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

50
Q

What is the best approach to remove 60 Hz line noise?

A

Use a stimulus rate that will put 60 Hz 180º out of phase on every other trial (40 Hz is great)

51
Q

Non-coherent Averaging (Induced)

A

-Averaging the frequencies together rather than the waves (trials)
-Advantage is that little timing differences don’t matter

52
Q

How does ABR change with intensity in normal responses?

A

There will be a predictable change in ABR with level; higher intensity results in higher amplitude waves

53
Q

In what frequency range is low pass filtering always set in ABR?

A

1500-3000 Hz (1500 is harder to get precise measures but 3000 has more noise so it’s personal preference)

54
Q

What are the 2 primary frequency bumps in the ABR?

A

500 Hz (2 ms separations allow us to see waves I, III, and V) and 1000 Hz (1 ms separations allow us to see waves I-V)

55
Q

In what frequency range is high pass filtering always set in ABR?

A

30-150 Hz

56
Q

When would you use a 30 Hz high pass filter compared to a 100-150 Hz high pass filter?

A

-Use 30 Hz if you want to see wave V more clearly
-Use 100-150 Hz if you want to see waves I and III more clearly

57
Q

Which ABR wave (I-V) is used for estimating thresholds?

A

Wave V

58
Q

T/F: sound level meters (SLM) have really fast integration that allow for use with ABR

A

FALSE: ABR occurs at a much faster rate than SLM integration (1/8th of a second)

59
Q

What is 0 dB HL?

A

The average behavioural threshold for pure tone

60
Q

What is 0 dB nHL?

A

The average behavioural threshold for clicks

61
Q

What is the peak latency per increase in dB?

A

400 us (0.4 ms) per 10 dB

62
Q

Why is the wave V L-I function steeper for low frequencies?

A

-Because the traveling wave makes it take longer to get down to the apex of the cochlea
-Across sound levels, there is a greater difference at low frequencies because more of the BM is stimulated with high sound levels (basalward shift)

63
Q

Which wave’s latency is most affected by stimulus rate?

A

Wave V latency is most affected with high stimulus rate due to synaptic delay (wave I is barely affected)

64
Q

Which waves’ amplitudes are most and least affected by intensity and rate?

A

Wave I amplitude is VERY affected by intensity and rate while wave V amplitude is LEAST affected by intensity and rate (wave V is robust so can still be recorded in bad conditions)

65
Q

Should you use a higher or lower stimulus rate when recording thresholds from wave V?

A

HIGHER stimulus rate should be used (40/s) since

66
Q

How is Wave V affected by noise?

A

Noise decreases amplitude and increases latency

67
Q

T/F: biological females have higher amplitude but longer latency values for waves III-VI

A

FALSE: they have higher amplitude AND shorter latency values

68
Q

How does Wave V latency change by gender with increasing hearing loss?

A

Females show little wave V latency change with increasing hearing loss, whereas wave V latency in males increases ~0.1 ms for every 20 dB drop in thresholds

69
Q

What are the theories for the sex difference?

A

-Differences in hearing sensitivity
-Body temperature
-Head size and brain dimension
-Physiologic and biochemical properties
-Likely greater travelling wave velocity in females and at young ages

70
Q

Are ABR results impacted by state of arousal?

A

No, even in extremely reduced states of arousal (such as narcolepsy or coma), ABR latencies and amplitudes remain intact

71
Q

How is ABR affected by drugs?

A

ABR is generally resistant to sedatives (e.g., Chloral hydrate) and anesthetic agents (e.g., Nitrous oxide)

72
Q

How does muscular artifact impact ABR?

A

ABR wave componentes can be completely obscured by excessive muscle artifact (often arising form neck or jaw muscles)

73
Q

Why is summing repeated measures helpful in ABR?

A

It will increase the signal-to-noise ratio by a factor of 1.414 (~40% improvement)

74
Q

What does subtracting repeated measures do for ABR?

A

Removes anything consistent in the response (aka it’s an estimate of background noise)

75
Q

What is smoothing?

A

Low-pass filtering; helpful with a noisy recording

76
Q

Summing responses to alternate polarity stimuli pros and cons

A

-Pros: reduces cochlear microphonic, reduces artifact
-Cons: reduces quality, does not improve SNR as much as summing same polarity, noise reduction should be the same as with single polarity summing

77
Q

Subtracting responses to alternate polarity stimuli

A

-Removes most of the response
-Preserves cochlear microphonic
-Preserves artifact

Electrophysiology (2 decks)

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