Final Exam AMLR Flashcards
AMLR,ALR,P300 (84 cards)
1
Q
For AMLR CANS alterations affect what wave component the most and why?
A
CANS alterations affect more the amplitude (μV) than the latency (ms) values in clinical analysis of middle and late responses
* Because there is little to no high frequency energy in the mid and late responses, precise latency resolution is less important
* But standard amplitude norms are lacking limiting clinical use
2
Q
AMLR & ALR’s reqire faster or slower rates and why?
A
- They require a slower recording rate compared to early AERs
- Because they are generated by larger and slower neurons subcortical and cortical neurons rather than the smaller stimulus-onset VIII N neurons
3
Q
What tests are more affected by neuromaturation?
A
AMLR’s are significantly more affected by neuromaturation than the ECochG & ABR
* become adult-like by about early adolescence to 10-12 years of age
4
Q
What age do AMLR’s become adult like?
A
Typically adult-like by about early adolescence to 10-12 years of age
5
Q
True or false
AMLR are not affected by state of patient while ALR’s are affected by the state of the patient.
A
FALSE
AMLR’s are affected by patient state, which the ECochG & ABR are not, including Sleep, sedation, attention, and cognition.
6
Q
Why are AMLR’s More affected by the state of the patient - Sleep, sedation, attention, and cognition compared to ABR’s?
A
- They have greater low frequency content and, therefore, are more affected by low frequency non-stimulus artifacts, often resulting in poorer morphology than the ECochG & ABR
- The fact that there may be a great variability in latency and amplitude values among normal listeners making it difficult to establish normative value, as well as greater artifacts during recording, limits the clinical use for these responses
7
Q
What AEP’s are Exogenous responses?
A
- early and middle latency responses (ECochG,ASSR,ABR,AMLR)
- AMLR- Central
- ABR - Peripheral
8
Q
What AEP’s are Endogenous responses?
A
- N2 is first endogenous auditory responses
- Attention usually changes the auditory late responses without affecting other auditory evoked responses
- depend on the psychologic or cognitive processing of stimulus
- N2 & P300
- Endogenous potentials provide clues to the nature of higher cognitive function
9
Q
All AMLR components are ____ Frequency ____ responses of the auditory system.
A
All AMLR components are Low Frequency exogenous responses of the auditory system.
10
Q
List the AMLR Components in order of latency
A
- Po: ~10 ms
- Na: ~ 20 ms (18 to 20 ms) Largest in Children
- Pa: ~ 30 ms (25 to 30 ms) Largest in Adult
- Nb: ~ 40 ms (Least recorded waveform)
- Pb ~ 50 ms (p1/p50 of ALR)
- Pb = Preattentive response, SG
Po & Pb are present less than 50% of the time under normal conditions
11
Q
At what age are the Na and Pa components of the AMLR become mature or “adult-like”?
A
Na and Pa components become mature or “adult-like” by 8 to 12 years of age
12
Q
At what age is Pa detectable in AMLRs?
A
90% detection at ~12 years of age
13
Q
To obtain reliable AMLR recordings in infants, subject sleep state needs to be controlled
* In children as young as 4 years Pa is detected when?
A
- Children are awake
or - In certain sleep stages such as
* Stage 1
* Rapid eye movement (REM) sleep
* Alpha stage (EEG waves observed during periods of relaxation but still awake)
AMLR is absent in the same children during
* Sleep stages 2, 3, & 4
14
Q
Does Sleep Stage affect AMLR results?
A
YES
Responses Present
* Stage 1
* (REM) sleep
* Alpha stage (EEG waves observed during periods of relaxation but still awake)
Absent
* Sleep stages 2, 3, & 4
15
Q
There is strong support in the literature that the overall AMLRs are generated by the what?
A
- inferior colliculus
- thalamus
- thalamocortical pathways
- the auditory cortex
16
Q
AMLR
Na is associated with neural activity from what?
A
Midbrain, thalamus, and thalamocortical radiation
20 ms
17
Q
AMLR
Pa is believed to be generated from where?
A
P.A
Primary Auditory cortex
30 ms
18
Q
What is PAM?
A
- Postauricular Muscle (PAM)
- reflex, that occurs at 12 to 20 ms. same latency range as the Na response
- recorded from electrodes positioned over the postauricular muscle behind the ear (mastoid placement of electrodes)
19
Q
When does PAM Occur?
A
- 12 to 20 ms, same latency range as Na.
- high intensity levels (+70 dB HL)
- recorded from electrodes placed on mastoid.
- PAM is a problem when evaluating the CANS
20
Q
What does Pb represent?
A
Pb represents “preattentive” brain activity
* Sensory Gating
21
Q
Offical Definition
What is Sensory Gating?
A
- Sensory gating is a preattentive natural response
- the brain’s ability to attenuate irrelevant sensory stimuli to prevent sensory overload and subsequent cognitive disturbances and to respond to a novel stimulus or a change in an ongoing stimulus.
22
Q
My Definition
What is Sensory Gating?
A
- Sensory gating is the brain’s natural filtering system.
- It helps the brain ignore unimportant or repetitive sounds so that it can focus on new or important ones.
- It happens before we’re even consciously aware — this is why it’s called “preattentive.”
- It protects the brain from becoming overwhelmed by too much sensory input (like background noise).
23
Q
What wave form reflects a individuals sensory gating ability?
A
Pb Or P50
- ratio less than 0.4 = good sensory gating.
- higher that 0.4 = poor sensory gating
- seen in schizophrenia, Alzheimer’s, autism, and traumatic brain injury.
- High ratios suggest that the prefrontal cortex, which normally helps control brain responses, isn’t working properly.
24
Q
What is the procedure of sensory gating?
A
two auditory stimuli (clicks or tones) → inserts.
* S1 (first stimulus)
* S2 (second stimulus) — identical to S1
* time between S1 and S2 is ~500 milliseconds.
* amplitude of the Pb response to S1 and S2 is measured.
* Calculate: S2/S1 = amplitude ratio
* ↓0.4 = Good sensory Gating
* ↑ ratio (closer to 1) = Bad SG
25
What does a higher Sensory Gating Ratio indicate?
Increased ratios = prefrontal cortex isnt working properly.
* affecting inhibitory control over subcortical & cortical regions
26
What conditions are consistant with high Sensory Gating Ratios?
* Schizophrenia
* Alzheimer’s disease
* Autism spectrum disorder
* Traumatic brain injury
27
How does sensory gating work?
Normal
* **Same Stimulus**
* S1 = excitatory Pb response.
* S2 = reduced (inhibited) Pb response, bc brain recognizes S2 as repetitive and reduced response to S2 (brain is filtering out unimportant information)
* **Different Stimulus**
* S1 = excitatory Pb response.
* S2 = Excitratory Pb Same size to S1 or larger because the stimulus was different & brain reflects ↑ attentional engagement.
28
# two channel
AMLR Montage
* Cz or Fz (noninverting)
* A1 & A2 (inverting)
* Fpz (ground)
| Key Differences is Inverting on ear lobes not mastoid bc PAM
## Footnote
Can do Mastoid but not preffered
29
Can you use the one channel AMLR montage when looking at hemispheric differences?
NO
* Midline electrode arrangement is inadequate for hemispheric responses because you will miss unilateral temporal lesions. Response needs to be measured on both sides.
* two or even three channel recording is preferred
* Vertex or midline (Cz) electrode will not pick up asymmetry (unilateral lesion); the normal side will dominate
30
What will a vertex or midline electrode not pick up asymmetry in AMLR?
Vertex or midline (Cz) electrode will not pick up asymmetry (unilateral lesion); the **normal side will dominate**
* Response needs to be measured on both sides.
* electrodes located over temporoparietal regions for identification/localization of cortical auditory dysfunction
31
# True or False
To ensure measurment of hemispheric differences there is a convention for placement of inverting electrodes sites with multi-channel AMLR recordings.
FALSE
* There is no convention for placement of inverting electrodes sites with multi-channel AMLR recordings
Important to remember
* right and left hemispheric non-inverting electrodes need to be symmetrical
* Lobe or mastoid electrodes can be used for inverting but mastoid are susceptible to PAM artifact
* Ground electrode for all channels is typically Fpz
32
AMLR Recoring Parameters
* Transducer:
* Stimulus:
* Polarity: any
* Level:
* Rate:
* Epoch:
* Sweeps:
* Transducer: insert earphones
* Stimulus: clicks or tone bursts (500 Hz tone bursts for Pb)
* Polarity: any
* Level: < 70 dB HL
* Rate: < 10 /sec (from 1 to 10 s)
* Epoch: 100 ms
* Sweeps: 500-1000
* More sweeps the longer the recording takes
33
Where is the Most power located in the AMLR?
| hz region
Most power of the AMLR is in the **30 to 50 Hz region**
34
The largest AMLR amplitude is obtained with what stimulation?
Largest AMLR amplitude is obtained with **binaural stimulation**
35
For AMLR Alterations in what filter setting exerts the greatest effect on responses?
Alterations in **high-pass filter** setting exerts the greatest effect on responses
36
What filter is never indicated for AMLR's?
A **notch filter** is never indicated for the AMLR because it removes spectral energy in the 40 to 60 Hz and may **remove AMLR components**
37
for AMLR what rate would result in a stable Pa
**1 to 10/s**
The AMLR can be recorded at a rate of 1/s to 10/s that would result in a stable Pa
38
Why dont you use a fast rate for AMLR's?
* AMLRs are generated by larger, slower, low frequency neurons with longer refractory periods
* With a fast stimulus rate, the neurons have less time to recover (repolarize) from the previous stimulus, thus less neurons are ready to fire synchronously in response to the new stimulus
* Rate Rate = Smaller AMLRs
39
For AMLR are clicks or tone burts preffered and why?
Prefered: **Low Frequency Tone burst (500hz)**
* Clicks can elicit the AMLR, a better response is elicited with a low frequency tone burst like 500 HZ, especially if Pb is the wave of interest
Why: tone burts have slower rates = larger reponses from neurons, gives the more time to recover.
40
# recording parameters
AMLR Intensity and why
< 70 db HL
* Less than 70
* bc High intensity levels >70 dB HL can produce the PAM reflex and other muscle artifacts that can interfere with the AMLR recording
41
What Artifacts affect the AMLR?
**Powerline noise** (50-60 Hz range)
* A good ground electrode will eliminate this
**Transducer-related stimulus artifact**
* Inserts should be positioned away from electrodes
**Eyeblinks and eye movements**
* Use good artifacts reject algorithm
**PAM**
* Occurs with mastoid electrode placement, stimulus level > 70 dB nHL
Note: Electrical artifact creates square waves
42
For AMLR what is the major component in children?
Na
43
For AMLR what is the major component in Adults?
Pa
44
In AMLR's what is the wave of interest for most diagnostic and neurodiagnostic purposes?
| older children and adults
Pa
45
# AMLR's
Po and Pb are present __ than __% of the time in normal listeners
Po and Pb are present **less** than **50%** of the time in normal listeners
46
# AMLR
Normal morphological variations for Pa include
**A sharp single peak for waves Pa and Pb separated by a distinct trough (1)**
A **broad Pa component** with
* Two rounded peaks
* A minimal trough between the two with the second peak well before the expected latency for Pb (2)
A **clear wave Pa** that may be
* Sharply peaked or
* Rounded with a broad base
* It may be followed by either a deep Nb trough or no apparent negative voltage trough (3's)
47
For AMLR prioritize waveform reliability by verifying _____
Like the ABR, for the AMLR prioritize waveform reliability by verifying **repeatability**
48
What is the most important measurement for AMLR and how do you measure it?
**Amplitude** (latency is very variable)
Measure: Choose Waveform of interest
* Peak to Baseline: Baseline is the average electrical activity before the stimulus. Fidning baseline can be challenging due to noise or baseline drift. Peak - baseline.
* **Peak to Trough:** The vertical distance from the peak of the wave to the most prominent negative deflection (trough) that precedes or follows it, i.e., Na-Pa or Pa-Nb
This method is often *preferred* as it can be more reliable and less affected by baseline shifts
49
____ & ____ of AMLR are more important than latency
**Amplitude & morphology** of AMLR are more important than latency
50
How can Amplitude of the ABR wave V also can be used in the analysis of the AMLR?
* Normally, Pa is twice the size of wave V in ABR
* Pa amplitude is significantly reduced if it is smaller than the amplitude of the ABR wave V, which is ~ 0.5 µv
* Pa smaller than 0.5 µv (microvolts) = reduced amplitude.
51
why are AMLR is more likely to be altered or not detected?
Not because of pathologies but because of methodological factors or subject parameters such as Electrode Placement and sleep stages
52
Cons to AMLR
Abnormal AMLR patterns are Not as easily detected because of considerable variation in normal waveform morphology & Scare normative Data
53
# AMLR
List how each affects the test
* Age
* Attention
* Sleep
* Drugs
**Age**: Must be considered, neuromaturation developing until ~12
**Attention**: Not affected
Sleep: Affected in stage 2,3 & 4 affect - so Pt's need to be awake
**Drugs**: *not* affected by nitrous oxide anesthesia and narcotic analgesics so can be recorded in most anaesthetized patients
54
AMLR Advantages over ABR
1. **Amplitude** of Pa is very large; (2x wave5) it enhances the SNR, which allows for response detection at a lower intensity level with less signal averaging.
2. Easily evoked by **frequency-specific tone bursts** with longer durations (500 Hz low frequency info) Allows for better frequency-specific information than the click-evoked ABR
3. Used the **same set-up and instruments** as ABR
55
# True or false
AMLR is used in conjunction with other AER's?
TRUE
AMLR is commonly used in conjunction with other AEPs, specifically the ABR
56
# True or false
AMLR is only used for evaluation of CANS disorders?
FALSE
AMLR can be used for **estimation of auditory thresholds** for cases when obtaining behavioral thresholds is inconclusive, unreliable, or cannot be determined such as
* Suspected malingering (nonorganic hearing loss) or
* Low cognitive status
57
The AMLR Pa response is within what db for threshold estimation?
The AMLR **Pa** response in older children and *adults* is within **~10 dB HL** of the pure tone behavioral response at the same frequency
58
Can ANSD be detected in AMLR?
Yes, AMLR can record ANSD even when ABR isnt able to
* AMLR can be recorded in *some* ANSD patients when an ABR cannot
* bc the AMLR is not as dependent on neural synchrony as the ABR
59
What is the Neurodiagnosis ability in AMLR?
* evidence to support that the AMLR is of value for evaluating **lesions/dysfunction of the CANs**, particularly in the *auditory cortex (temporal lobe) and thalamocortical connections*
60
Where does AMLR mostly elaluated for lesions/dysfunction of the CANS?
auditory cortex (temporal lobe) and the thalamocortical connections.
61
# AMLR
Reduced or absent wave forms indicates what?
Reduced or absent → temporal lobe lesions on the affected side.
62
Interhemispheric amplitude difference for the Pa reflects what?
The interhemispheric amplitude difference for the **Pa** component reflects the **side of the cortical lesion** regardless of which ear is stimulated
* Side Pa ↓ = Side of Cortical lesion
| interaural amplitude difference
63
How is AMLR able to detect interhemispheric amp differences?
* The Na and Pa have bilateral generator sites located within the temporal lobes
* Therefore, patients with unilateral lesions present with a reduced or absent Pa over the involved temporal lobe but unchanged for the contralateral lobe
64
AMLR asymmetries were not detected for cortical lesions that did not affect the ____ lobes
AMLR asymmetries were not detected for cortical lesions that did not affect the **temporal** lobes
65
Can AMLR be used for TBI assessment?
Yes
* AMLR is an indicator of how well or how poorly the patient will recover from the TBI
* More severe the TBI = reduced amplitude of the Na and Pa
| Shown in Study
66
what do AMLR waveforms look like in a TBI?
More severe the TBI = reduced amplitude of the Na and Pa
* unilaterally or bilaterally with the Pa-Nb amplitude < 0.3 µV = abnormal
67
AMLR can help in assessing what?
* Neurodiagnostic: lesions/dysfunction of the CANs
* TBI: reduced amplitude of the Na and Pa = bad
* Central Deafness: reduced amp
* Dementia & Parkinson's: abnormal Pb
* MS: Increased latencies - Pa and Pb
* Stroke: used to monitor effectiveness of therapy.
68
Can AMLR be used for CAPD assessment?
Not consistent pattern with APD
* not indicated a specific, consistent, and reliable pattern of AMLR responses for (C)APD that may be useful clinically
69
Can AMLR be used for Central Deafness assessment?
YES
* The ABR can also be normal
* The AMLR and ALR will be abnormal because of the lesion(s) in the temporal lobe and auditory cortex
70
Can AMLR be used for Dementia assessment?
Yes
Parkinson’s & Dementia
* Normal Na & Pa Latency
* Pb is abnormal/absent
71
Central or cortical or deafness occurs when ....
Central or cortical or deafness occurs when **both primary auditory cortices (Heschel’s gyri) and/or subcortical regions are damaged**
72
Most common cause of Central Deafness
stroke
73
Why will AMLR be abnormal in central deafness?
AMLR and ALR will be abnormal because of the lesion(s) in the temporal lobe and auditory cortex
74
# True or false
Parkinson’s showed greater Pb abnormality than the Alzheimer’s patients
TRUE
* Parkinson’s disease showed greater Pb abnormality than did the Alzheimer’s patients
* Showing both a delayed Pb latency and reduced amplitude
75
Can AMLR be used for MS assessment?
YES
* Increased latencies of the Pa and Pb
* or absence (50% of time)
76
How can you increase the sensitivity of diagnosing MS?
Efficacy of using the **ABR, AMLR, and ALR** showed greatly increased sensitivity of diagnosing MS compared to either AER alone
77
Can AMLR be used for strokes assessment?
Yes
* In strokes AMLRs are related to recovery of aphasia
* Nb peak can be used to monitor effectiveness of therapy
78
Abnormal (deficient) Pb sensory gating is reportedly observed in the following conditions:
* Alzheimer’s Disease
* Schizophrenia
* Mania
* PTSD
* Autism Spectrum Disorder
* TBI
79
Clinical advantages of AMLR
* Origin in the auditory cortex
* Lateralize auditory cortical dysfunction
* Present in young children
* Can evoke the response with tonal and other complex stimuli (speech)
* Sensitive to the reticular activating system
* Can assess sensory gating mechanism
* Assess CI function
80
How can AMLR Assess CI Funtion?
* Pb matures at the same rate in children with CI as in normal children
* Maturity of Pb was delayed by amount of time equal to the duration of deafness
81
Limitations of AMLR
* Artifact issues
* Subject and subject state issues (Patient cannot be in certain sleep stages)
* Considerable variation in normal waveform morphology
* Abnormal responses that vary with differing recording conditions
* Cannot say where the issue is because of the multiple generators.
82
Patients with cortical deafness will not be able to understand __ or __
Patients with cortical deafness will not be able to understand **speech** or recognize **environmental** **sounds**
83
In central deafness peripheral auditory function are ....
all tests of peripheral auditory function are **normal** including immittance measures
except **WRS - Poor**
84
Central Deafness Test results
* Audio: Normal
* WRS: Poor
* ABR: Normal
* AMLR: Abnormal decrased amp
* Unable to understand speech or recognize environmental sounds
