Lecture 3 Flashcards
ABR is happening up to about ____ms
6 (typically 5.5ms for wave V)
A click ABR typically gives the ____ peaks
5
What direction is ABR measured?
Positive up
What does the ABR reflect?
- Action potentials (not graded post-synaptic potentials)
- Requires highly synchronized activity
Do the action potentials line up for ABR?
- Yes
- The peripheral auditory system is very temporally precise
-Many neurons fire at precisely the same time to things like stimulus onset
The auditory nerve is about ____ fibers
30,000
What is the closed field problem with ABR?
Action potentials don’t give rise to open-fields
Where do sinks occur? Where do the sources occur?
- Sinks occur progressively at each break (Node of Ravier) in the myelin sheath
- Adjacent areas are passive sources
What 2 ways can we break the symmetry to allow for action potentials to give rise to open-fields?
- Direction change in axon can set up a pseudo-dipole
- Change of impedance surrounding axon
Where is the impedance changing?
Impedance change between the internal auditory meatus and cranial cavity
The ABR is a ____ response
Subcortical
Do subcortical nuclei give rise to open-field
No
Do all ABRs look the same?
No, we get various morphologies and shapes
Typically, Wave ____ is larger than wave I
V
Wave ____ and ____ are often conjoined
IV, V
Should you rely on amplitude differences when comparing ABRs?
No (amplitudes can be variable)
What waves are horizontal?
Waves I, II, and III
What waves are vertical?
Waves IV, V
What 3 ways do you find the ABR generators?
- Correlate with near field activity
- Introduce lesion (freezing)
- Source localization
What is the most common way to find ABR generators?
Correlate with near field activity
Why is it hard to determine the generators for ABR?
It happens in the middle of the head in the brainstem
Explain ABR generators and complexity
- 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
Earlier peaks are ____, later peaks are more ____
Simpler, complex
Everything travels along the ____ to get to the brainstem
Auditory nerve
What is the speed of the basilar membrane?
2.8 m/s or 2.8 mm/ms
How many ms does it take to get from 10kHz to 250Hz?
8ms
How many ms does it take to get from 4kHz to 500Hz?
4ms
What is the speed of the VIIIth nerve?
22 m/s or 22 mm/ms or 2.2 cm/ms
Where do two other delays take place? How long are the delays?
- Cochlear filter build-up time at CF (0.5ms)
- Synaptic delay (1ms)
What is the length of the VIIIth nerve?
2.6cm
How do we localized ABR components?
Speed and distances
Is the BM fast or slow?
The BM is very slow part of the body (HF at the base, LF at the apex – traveling slow)
High frequencies are at the ____
base of the BM
Low frequencies are at the ____
apex of the BM
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)?
8ms
Each synapse add about ____ms
1
How long does it take to get down the VIIIth nerve?
A little over 1ms (2.6cm long)
Which wave is the iffiest?
Wave IV
What waves are the most reliable?
Waves I, II, III, and V
Wave I typically happens at ____ ms
1.7
Wave II typically happens at ____ ms
2.8
Wave III typically happens at ____ ms
3.9
Wave IV typically happens at ____ ms
5.1
Wave V typically happens at ____ ms
5.7
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?
- 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
Where is wave I generated?
- Wave I arises from the distal (outside) portion of the VIIIth nerve
Latency of wave I is the same as the ____
- Compound action potential (CAP)
- Wave I is the CAP
Where is wave II generated?
- 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)
Where is wave III generated? Where is it recorded?
Cochlear nucleus (recorded from the wall of the 4th ventricle)
Where is wave IV generated? How is it generated?
Superior olivary complex (generated contralaterally)
Where is wave V generated? How is it generated?
Lateral lemniscus (generated contralaterally)
Why is wave V not generated at the inferior colliculus?
Wave V terminates at the inferior colliculus
What does the inferior colliculus generate?
SN10 (slow negativity 10) which happens after wave V
How do you get rid of the ABR?
- Damaging the globular and bush cells in the AVCN
- The AVCN is what gives us sound localization
What frequencies drive the ABR generators?
Driven primarily by high frequencies (above 2000Hz)
What 3 ways do you measure the amplitude of ABR?
- Peak
- Peak-to-peak
- Interpeak ratio
What 3 ways do you measure the latency of ABR?
- Absolute
- Interpeak
- Interaural
Do we rely on amplitude or latency measures more?
Latency (when the peak occurs)
What is absolute latency?
When a wave occurs based on the stimulus
What is interpeak latency?
When did wave x happen according to wave x (the timing difference between two peaks)
What is the best latency measure?
Interpeak
Latency measures are more ____
Stable
Where do you measure wave I?
The center of the peak
Where do you measure wave I if you have two peaks?
From the second peak
Where do you measure wave II?
The center of the peak
Where do you measure wave III?
From the center, but you often have two little peaks, so look for the mid point (middle)
Where do you measure wave IV?
The first bump on the IV-V wave
Where do you measure wave V?
The shoulder of the IV-V wave (the very edge)
Standard deviation between absolute latencies is roughly ____ms
0.2
What waves may have bifid peaks?
I and III
What 3 ways do you get rid of a bifid wave I?
- Decrease intensity
- Change montage
- Pick second peak
What do you do with the bifid peak on wave III?
find the midpoint
How can you separate waves IV and V?
Contralateral recording
What 4 things are seen in a contralateral recording?
- IV is .1-.5 ms earlier in contralateral recording
- Wave I is absent
- II is larger
- III is smaller
Placing electrodes on each ear gives us a ____ montage
Horizontal
How do we get a horizontal montage?
Can be derived from an ipsi/contra montage
How many channels do you need?
Two
What does a two channel recording give you?
Ipsi, contra, and horizontal
We are more concerned with the ____ measure
Ipsilateral
Why might we want a contralateral recording?
Cross hearing
What kind of response is an ABR?
An onset response (transient)
What type of stimuli is being used for an ABR?
A click (on or off, which is transient)
Where does a click have energy?
At all frequencies
What is a null?
The end of a click life
We use ____ micro second click because it gives us a null at ____ Hz
100, 10,000
Where is the peak energy in an ABR? Why?
3 kHz (because of the filtering properties of the ear)
What happens to an ABR if the individual has hearing loss?
The ABR will shift because it starts from a different spot on the cochlea
What is a different stimuli that can be used for ABR?
A tone burst
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 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
What does windowing improve?
Windowing can improve place specificity (how fast it is turned off and on)
What are the 4 different types of windowing?
- Trapezoid
- Triangular
- Cosine squared
- Blackman
What is the most common type of windowing?
Blackman (has a more narrow peak)
What are the 2 types of stimulus polarity?
- Rarefaction (going away from the ear)
- negative pulse
- depolarizing
- Condensation (going towards the ear)
- positive pulse
- hyperpolarizing
____ gives you the first peak
Rarefaction
____ peaks are happening slightly earlier than ____ peaks
Rarefaction, condensation
What polarity is often used in ABR?
Alternating polarity
What is alternating polarity?
Combine rarefaction and condensation
What is the problem with alternating polarity?
- They do not overlap perfectly (therefore alternating polarity gives you an ABR that is not quite as clear)
Why do we do alternating polarity for ABR?
- Stimulus-related electrical artefact
- Cochlear microphonic (inverts with the stimulus)
Amplitude of the ____ is proportional to the reciprocal of the square root of the number of trials
Noise
Noise amplitude is 2x as low with ____x number of trials
4
noise amplitude is 4x as low with ____x number of trials
16
noise amplitude is 8x as low with ____x number of trials
64
The more trials, the lower the ____
Noise
What should we do to remove 60Hz?
Use a stimulus rate that will put 60 Hz 180° out of phase on every other trial
60 Hz period is ____ms
1000/60 = 16.666ms
What is the half period of line noise?
8.3333 ms
If we want a trial to be in the opposite phase of 60Hz what do we do?
- 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)
Is 30Hz a good stimulus rate?
- 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
Is 40Hz a good stimulus rate?
- 1000/40 = 25 ms
- 25/8.3 = 3 times the 1/2 period of line noise
- This is a great stimulus rate!
What are 3 good stimulus rates?
17.14, 13.33, 10.91 Hz
Explain non-coherent averaging (induced)
- 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
What are 4 subjective methods for detecting responses?
- Subjective detection by single person
- Subjective detection by multiple people
- Response replication
- Response tracking
How many tracings do you need to do for ABR?
two
T/F: the waves have to be repeated to be marked
True
What do you do if you can only get one tracing?
Divide it in two
How does visual inspection and replication work?
- Two runs of 2500 sweeps
- They don’t overlap very well (can only see wave V)
- Looking to see if any waves repeat/overlap
How does response tracking work?
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)
What frequency do we typically high-pass for threshold?
30Hz
What frequency do we typically high-pass for diagnostic?
100Hz
How we ____ changes the amplitude
Filter
What does high pass filtering do?
Gets rid of LF energy, line noise, things we don’t want, noise
What does low pass filtering do?
Prevents aliasing
What is the narrowest frequency range of ABR?
150-1500Hz
What is the typical range for the low-pass filter?
1500-3000Hz
A high-pass filter of ____Hz is good for showing wave V
30Hz
A high-pass filter of ____Hz is good for showing waves I and III
150Hz
Wave amplitude changes as a function of ____ filtering
High-pass
What do you need to do before using a sound level meter?
Make sure it is measuring correctly
What level should almost all SLMs present?
94dB (1 volt)
SLM fast integration ____ of a second
1/8th
How does calibrating the stimuli work?
- 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
What is 0 dB HL?
0 dB HL is average behavioral threshold for pure tone
What is 0 dB nHL?
0 dB nHL is average behavioral threshold for click
We need to convert ____ to ____ for ABR
HL, nHL
Recording parameters: rate? polarity?
- Rate: 39.1/s
- Polarity: alternating
Explain the latency-intensity function
- About 40 µs per dB, OR
- about 400 µs (0.4 ms) per 10 dB
Explain the latency-intensity function graph (clicks)
- 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
What is the only wave you get at soft levels?
Wave V
L-I function for tone bursts
- LF (500Hz), wave V latency = 15ms
- HF (8000Hz), wave V latency = 9ms
Why are functions steeper for low frequencies?
- 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
Wave ____ is less delayed than earlier peaks, as level is decreased
V
Since early waves are more delayed at low levels, ____ latency is smaller at low levels
I-V
Do stimulus rate and response latency affect wave I?
For wave I, latency is not (or barely) affected by stimulus rate
Are waves II-V affected by stimulus rate and response latency?
- Waves II-V
- Latency increases, amplitude still decreases
- Rate-related delay is synaptic delay—increases with number of synapses
- Wave V latency most affected
Do stimulus intensity/rate and response amplitude affect wave I?
Wave I amplitude is very affected by intensity and rate
Do stimulus intensity/rate and response amplitude affect wave V?
- 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)
Wave V is very ____
Robust (can be recorded in the worst conditions)
- Can go fast and slow
Wave I is very ____
Delicate
- Needs to be slow and high
What 2 things are unique about wave V?
- 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!
Noise decreases ____ and increases ____
Amplitude, latency
Wave V amplitude fairly resilient to rate, but not to ____
Noise
Wave V latency similarly affected by ____ and ____
Noise, rate
Recording parameters - electrodes
- Cz / Fpz to M1/M2 (A1/A2)
- M = mastoid, A = auricle
Recording parameters - filter
- 30/100 Hz –> 1500/3000 Hz
- 100Hz is for diagnostic ABR (wave I and III)
- 30Hz is for thresholds (wave V)
Recording parameters - averaging
1000-2000 (2000 most often)
Recording parameters - rate
- 10.1-39.1/s
- Slow rate is typically for neurodiagnostic
- Thresholds typically use a high rate and a low filter
Recording parameters - stimulus
- 100 µs click / 2-1-2 tone-burst
- Often blackmen window
Recording parameters - rejection
+/- 25 uV
