Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AUD spring 2020 Electrophys II > Week 13: ASSR > Flashcards

Week 13: ASSR Flashcards

1
Q

Basic what is ASSR

A
  • an evoked potential

- –instrumentation/recorded similar to ABR, insert earphones, surface electrodes, averageing computer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

stimuli used for ASSR

A
  • pure tones
  • –this means the responses are frequency specific because ASSR uses pure tones
  • —–this is not a tone burst!
  • steady state
  • –this implies that the tone envelope starts before the envelope of the last tone fully ends
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

why are ASSR steady-state and not transient

A
  • a transient sound would be a click or tone pip
  • –very brief
  • –stops and starts
  • steady state
  • –is a continuous sound
  • –a sound that doesnt stop
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

how is the ASSR waveform generated

A
  • presenting stimuli at high repetition rate leads to an overlap of responses to successive stimuli
  • –the transient response to one stimulus overlaps with the responses to succeeding stimuli
  • the response is a complex periodic wave
  • –an ongoing response to an on-going stimulation
  • it is phase locked to the modulation envelope of the stimulus rate
  • you cannot label individual wave on an ASSR since the response is a sine wave and thus an overlapping of transient responses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what are the ASSR generators of an 80 Hz ASSR

A
  • the ABR sites
  • mainly brainstem and less primary auditory cortex (supratemporal plane)
  • ASSR has an equivalent latency of around 10 ms, suggesting late brainstem generators (wave 5)
  • note 80 Hz is considered a fast rate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what are the generator sites for a 40 Hz ASSR

A
  • really between 20-60 Hz
  • these are the AMLR sites
  • mainly cortical or thalamic origin (less brainstem)
  • auditory cortex, but most likely subcortical
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are the generator sites for a <20 Hz ASSR

A
  • the auditory cortex

- –like the ALR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

ASSR recording montage

A

*similar to ABR but make sure that you are set up to record from the response generator site that corresponds with the frequency of modulation you are using

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what are the two ways you can use to see an ASSR response

A
  • time domain
  • –phase which can be converted to latency
  • –shows as a sine wave recording and the frequency can be seen by the time between each response
  • the frequency domain or spectral analysis
  • –this is most commonly used
  • –the x-axis is the frequency and the modulation frequency is shown by the red line, everything else in the low freqs are artifact
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what us the carrier frequency for an ASSR

A
  • the test tone
  • the pure tones which are frequency specific and are used to stimulate the response
  • do not just use one, use four to stimulate response in one ear simultaneously
  • 500, 1000, 2000, 4000
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

modulation frequency

A
  • labels the “test” frequency
  • –such as 40 Hz or 80 Hz
  • –the brain detects and entrains upon the modulation
  • this dictates where you are testing from
  • each carrier frequency must be assigned a different modulation frequency to be able to see the response from each carrier frequency instead of just a singular response in the frequency domain (need those peaked lines separate)
  • –need to have at least 2 Hz between modulation frequencies so there is not an overlap on the response on the basilar membrane
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

why must you use unique modulation frequencies

A
  • this allows multiple Fc to be tested simultaneously
  • –in one ear or both ears
  • –as long as each Fc (carrier frequency) has a different modulation frequency (MF) in order to differentiate the responses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what happens to each frequency stimuli at the cochlear level

A
  • at the cochlea the stimulus is broken down in to its separate frequencies
  • the four separate stimuli are combines in the time domain and are presented to the subject as complex tonal stimuli
  • because the cochlea is tonotopically organized by 4 tones are each sensed by the respective tonal area on the basilar membrane
  • with hearing impaired you might get a big response to 500 Hz and smaller for other freqs for sloping HL
  • –but with recruitment could see even larger amplitude for 4000 Hz
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

EEG response of multi-frequency ASSR

A
  • when each carrier frequency is modulated at a different rate
  • –the electrical response appears at different points i the EEG spectrum
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does the ASSR screen look like with interacoustics

A
  • 6 minutes duration
  • green means a response, red equals no response
  • the y-axis shows the confidence level of here being a response
  • –waiting to turn green until it is statistically significant at p>0.05
  • x axis is the timeline from 0-6 minutes
  • will keep testing the carrier frequencies until a decision is made for them and then that one will stop and will continue until all have stopped
  • –you then draw the audio based off of the response
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

super basic 4 step process of how an ASSR works

A
  • the stimulus tones are composed of a primary stimulation frequency or Fc
  • the cochlea is stimulated at the site of the Fc
  • the stimulus onset caused by the AM and/ or FM generates evoked potentials that follow the RR or MF
  • the response is measures using spectral techniques at the RR or MF
  • –AM is amplitude modulation and FM is frequency modulation
  • —–what we are talking about with pure tones is AM because FM would be a warble tone
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

ASSR electrode montage

A
  • Fz (or Cz) referenced to nape of the neck or
  • Fz or Cz to ipsi mastoid (M1, M2)
  • –80 Hz is an Fz montage because recording from the brainstem
  • –use Cz for 40 Hz modulation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

bandpass filter for ASSR

A

30-300 Hz

  • or 1-300 Hz but pt needs to be really quiet if using 1-300
  • –also system uses statistical criteria based on normative data
19
Q

sweeps with ASSR

A

12, 32, or 46 blocks

  • –use more sweeps for threshold searching
  • –the more sweeps the better the S/N ratio
20
Q

ASSR stimuli options

A
  • continuous tone/bursts of stimuli that is modulated in amplitude, frequency, or both
  • –amplitude modulation (AM) of a continuous tone
  • —–minimum modulation
  • –frequency modulation (FM) of a continuous tone
  • —–is a warble tone, CF and one tone on each side at 10%
  • –mixed modulation of a continuous tone
  • —–gives the most robust response
  • –exponential amplitude modulation envelope (AM^2)
  • —–gives better response but not much research here
  • –IAFM of a continuous tone
  • —–this is independent amplitude frequency modulation, this will be more complex and represent the speech stimulus, great correlation with WRS
  • other stimulus such as white noise, clicks, chirps can be used
  • –note that narrow-band chirps provide highly synchronized stimulation of specific freq bands
  • —–allows for faster data collection that is 1/2 normal ASSR data collection time
21
Q

benefit of a chirp ASSR

A

compensates for traveling time of the click stimulus and thus will give larger waves (octave-band delay-compensated stimuli)

22
Q

amplitude modulation on ASSR

A

change in the amplitude of the stimulus over time

  • the amplitude of the response increases as the depth of the modulation increases
  • –saturates at a depth of about 50%
  • –the response is better with higher modulation depth because the neurons are responding to the variations in the CF tone
23
Q

frequency modulation on ASSR

A

*changes in the cochlear stimulation site resulting from frequency modulation elicit responses

24
Q

mixed modulation (MM) stimuli for ASSR

A
  • AM and FM
  • the timing relationship between the maximum amplitude and maximum frequency is critical in eliciting optimal responses. The two should coincide in order to elicit the largest response possible
  • –combining AM and FM has a dual effect on the cochlear generation site, thus producing a larger effect than either aone
25
Q

40 Hz ASSR repetition rate

A
  • is basically an AMLR to repeated tone bursts at a 40Hz repetition rate
  • very large response but is unreliable in infants
  • –high repetition rate is a smaller response but is not affected by sleep
26
Q

how is ASSR a computerized decision

A
  • there is an automatic detection response determination
  • using an F statistic, a response is determined to be present, if the SNR is 613 dB (p<0.1) above the noise at the frequency bin corresponding to the MF and 5 Hz on either side
  • recordings are acquired using a split-buffer technique which allows comparison of signal and noise characteristics at each freq
27
Q

judging an ASSR response polar plot

A
  • if the response in the polar plot is at the center area, there is no response
  • if the response extends beyond the center area there is a response
28
Q

phase coherence (PC) with ASSR

A
  • tests whether brain waves meet a statistical criterion for “phase locked”
  • 0 is no response to 1 which is a response
  • –when they are in phase the values are closer to 1 and if they are random are closer to 0
  • related to SNR
29
Q

magnitude squared coherence (MSC) with ASSR

A
  • phase and amplitude’
  • another technique related to SNR
  • –utilizes both the phase info and amplitude info; looks at how much of the response is truly the response instead of just noise
30
Q

effect of intensity of ASSR response

A

*increase in intensity level up to 90 dB HL leads to amplitude increases and latency decreases

31
Q

effect of modulation frequency on ASSR response

A

larger response with slower MF

32
Q

the effect of the carrier frequency on the ASSR response

A
  • the 40 Hz response decreases in amplitude with increasing carrier frequency
  • for the 80-100Hz response, the amplitude if larger for mid-freqs (1 and 2 kHz) than fro higher or lower freqs
33
Q

effect of age on 80 Hz ASSR responses

A
  • these responses are reliable in newborns and in sleeping children
  • in the first few months of life
  • –smaller responses that are 1/3 to 1/2 the size of the adult response
  • –increases over the 1st year with greater change to higher Fc
  • –thresholds are 10-15 dB higher
  • greater phase delay mainly at 500 Hz in newborns
  • with increasing age
  • –no significant change in the amplitude or phase
34
Q

sleep and arousal on ASSR

A
  • > 70 Hz response
  • –no significant sleep effect on the response
  • 40 Hz response
  • –the amplitude during sleep is about 1/2 that of that recorded during wakefullness
  • attention hasnt been studied with high MF
35
Q

ASSR applications

A
  • mainly used for threshold determination
  • strong correlation with ABR and 2000 and 4000 Hz ASSR
  • may have some advantages over the ABR because about 1/3 pts with severe to profound HL have no ABR but measurable ASSR
36
Q

ASSR and threshold preditcions

A
  • with 60+ dB HL you can get within 5-10 dB of threshold using their regression, but if hearing is better than 60 dB, hearing is 10-15 dB better than prediction with regression
  • –recruitment makes severe HL ASSR thresholds closer to the actual threshold
37
Q

ASSR test time

A
  • 19 minutes (Luts and wooters)
  • 21 minutes (perez-abalo et al)
  • 45-60 minutes typical (john et al, kaf et al)
38
Q

neurologic application of ASSR (40 Hz)

A
  • 40 Hz response
  • –reduced in pts with brainstem or thalamic lesions and dyslexia pts
  • not affected in pts with unilateral temporal lobe lesion
  • absent in comatosed pts and pts with brain death
  • to monitor the level of anesthesia during surgery
  • –but some say dont do this
39
Q

neurologic applications of ASSR (90 Hz)

A
  • at 90 Hz is good for auditory neuropathy
  • note you cannot record an ABR response to track threshold with AN
  • with ASSR you will see higher thresholds in children with AN
  • absent ASSR with the presence of near normal PTA suggest AN?
40
Q

BIC and ASSR

A
  • latency, not amplitude, for the ABR and 80 Hz ASSR BIC suggest presence of similar BI mechanisms at the brainstem
  • both amplitude and latency of AMLR BIC and 40 Hz ASSR BIC suggest presence of different BI mechanisms at the subcortical level
41
Q

advantages of ASSR

A
  • it is objective (using stats and F-technique)
  • frequency specific stimuli (as TB ABR)
  • –but faster than TB ABR
  • several AM stimuli– simultaneously
  • accurate
  • –particularly at higher HL, above 40 dB HL
  • –at severe and profound HL
  • useful for eval of threshold up to mild hearing loss
  • commercial availability
42
Q

limitations of ASSR

A
  • thresholds–different testing protocol
  • –the more CF you use the smaller the amplitude of responses
  • –AM, MM, exponential , etc
  • –p<0.05 or P<0.01
  • –noise criterion
  • –stopping rules
  • non flat loss leads to longer testing time
  • infants have limited clinical data for infants with HL
  • –limited BC-ASSR in infants
  • high stimulus levels leading to artifact and non-auditory/vestibular response
  • generators are not exactly sure and are not as well confirmed as with ABR
  • neurologic diseases
  • –differential diagnostic value is not established
  • is not a stand alone test for objective dx of HL
  • does not have its own CPT code
43
Q

does ASSR stand alone for ERA

A

*no it must be combined with click and toneburst ABR

44
Q

areas of further research in ASSR

A
  • maturational effects
  • effects of sedations
  • agreement with pure tone audiogram and time to complete using different protocols
  • neuropathologial cases
  • optimizing Fc-MF
  • use of simusoidal 40 Hz ASSR
  • NB chirps ASSR
  • refinement of objective detection algorithm
  • —use of phase/amplitude weighting
  • –use of adaptive filtering (noise weighting)

AUD spring 2020 Electrophys II (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions