Chatty Flashcards quiz 1
(228 cards)
1
Q
What is spontaneous neuroelectric activity in the central nervous system?
A
In the absence of sensory stimulation, the central nervous system generates spontaneous and random neuroelectric activity. This can be recorded as a potential difference using scalp electrodes.
2
Q
What forms the basis of the electroencephalogram (EEG)?
A
The electroencephalogram (EEG) is based on recording the spontaneous and random neuroelectric activity of the central nervous system using scalp electrodes.
3
Q
How can neural activity in response to sensory stimulation be detected?
A
Neural activity that occurs in response to specific types of sensory stimulation can be extracted from the EEG data.
4
Q
A
5
Q
What are some examples of early neural responses detectable in EEG?
A
Early responses detectable in EEG include the Electrocochleography (ECochG) and Auditory Brainstem Response (ABR). These are typically much smaller than the overall EEG signal.
6
Q
What techniques are necessary to view all evoked responses in EEG?
A
To view all evoked responses, especially those much smaller than the EEG like ECochG and ABR, techniques such as signal averaging and amplification are required.
7
Q
What are Evoked Potentials (EPs) or Evoked Responses (ERs)?
A
EPs or ERs measure the electrophysiologic responses of the nervous system to a variety of stimuli.
8
Q
Can any sensory modality be tested using EPs/ERs?
A
In theory yes, almost any sensory modality can be tested using EPs/ERs.
9
Q
Which evoked responses are most frequently measured in clinical practice?
A
- Visual Evoked Responses (VERs),
- Short-latency Somatosensory Evoked Responses (SERs),
- Short-latency Brainstem Auditory Evoked Responses (BAERs), and
- Cortical Evoked Responses.
10
Q
What do Visual Evoked Responses (VERs) test?
A
VERs test the electrophysiologic responses of the visual system to stimuli.
11
Q
What do Short-latency Somatosensory Evoked Responses (SERs) measure?
A
SERs measure the electrophysiologic responses of the sensory pathways to stimuli.
12
Q
What do Short-latency Brainstem Auditory Evoked Responses (BAERs) assess?
A
BAERs assess the electrophysiologic responses of the auditory pathways, at the level of the brainstem.
13
Q
What are Cortical Evoked Responses?
A
Cortical Evoked Responses include late latency responses and the P300, measuring the cortical processing of stimuli.
14
Q
What are Somatosensory Evoked Responses (SERs)?
A
SERs are responses generated by the stimulation of afferent peripheral nerve fibers, either through physiological or electrical means.
“Afferent” the nerve signals moving towards the central nervous system.
15
Q
How are SERs typically generated for clinical diagnostic studies?
A
Common Stimulation Sites for SERs:
* Median Nerve: At the wrist.
* Common Peroneal Nerve: At the knee.
* Posterior Tibial Nerve: At the ankle.
16
Q
Where are recording electrodes placed for SERs?
A
Recording electrodes for SERs are placed over the scalp, spine, and peripheral nerves proximal to the stimulation sites.
17
Q
What clinical diagnoses benefit from the use of SERs?
A
SERs are useful in diagnosing
* neurologic diseases,
* determining the prognosis of comatose patients, especially after a postanoxic coma, and for
* intraoperative monitoring of “at risk” somatosensory pathways.
18
Q
What characteristics of SER waveforms are typically analyzed?
A
Characterizing SER Waveforms:
* Morphology: shape and structure of the waveform.
* Amplitude: The height of the waves, indicating the strength of the response.
* Dispersion (Latency): The time delay in waveform response, indicating the speed of nerve conduction.
19
Q
What are late evoked responses used for in neurological studies?
A
Late evoked responses are used for studying higher cortical functions.
20
Q
Give an example of a late evoked response and its application.
A
P300 used to study Alzheimers
* P300 response is an example of a late evoked response, often studied in relation to Alzheimer disease.
21
Q
What is the current clinical usefulness of late evoked responses in audiology?
A
Clinical use of late evoked responses in audiologiy is currently limited, considered experimental and not routinely or widely used (in AuD or Neuro)
22
Q
is their future potential of late evoked responses in audiology?
A
Yes, Late evoked responses show promise and may prove to be useful for clinical practice in the future.
23
Q
How has the clinical use of Evoked Responses (ERs) changed over time?
A
clinical use of ERs has decreased due to advances in imaging technology, especially MRI.
24
Q
What is the basic difference between Evoked Responses (ER) testing and MRI?
A
MRI
* MRI is an Imaging/structural/anatomic test that provides accurate information about structural problems
ER
* ER testing assesses functionality and physiology of anatomic pathways, offering less spatial or localizing information.
25
Why are most clinical questions of the involved neurologic structures better answered by MRI rather than ER testing?
MRI provides more detailed and accurate structural information, making it more suitable for addressing most clinical questions about neurologic structures.
26
In what scenarios might MRI and Evoked Responses (ERs) be complementary?
In some cases, MRI and ERs may be complementary, as MRI provides structural details and ERs provide functional information.
27
What ar Auditory Evoked Responses?
AER's are brain waves or eletrical responses generated when the auditory system is stimulated by sound.
28
What types of sounds are used to elicit AERs?
clicks (abrupt onset, very short duration, broad band),
tone bursts (short duration, frequency specific), and
speech sounds (e.g., /ba/ and /da/).
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How does stimulus intensity affect AERs?
the louder the stimulus intensity, the larger the AER response.
30
how are sounds presented during AER testing?
Sounds are presented via an acoustic transducer (insert)
31
How is activity from the cochlea and brain evoked by sound stimulus captured?
Activity is picked up by electrodes typically placed
* on the scalp such as the vertex or high forehead, near the ears on the ear lobes or the mastoid.
32
What is the typical structure of an electrode used in AER testing?
electrode consists of a wire with a metal disc or adhesive patch at one end that makes contact with the skin, and the other end has a DIN pin that plugs into an electrode box or preamplifier.
Wire -- metal disc or adhesive -- other end has DIN Pin ---> DP plugs into electrode box or preamplifier
33
What is a DIN connector?
A DIN connector is an electrical connector
* initially standardized for analog audio signals
34
How common are DIN connectors today?
DIN conncetors are no longer being made and have been replaced with equivalent international IEC standard.
35
What is meant by "far field recording" in the context of AERs?
Far field recording refers to the activity evoked by the **sound occurring from structures at a distance** from the electrodes, which captures sensory and neural activity transmitted through body tissues and fluids to the surface electrodes.
Far Field = sound occurs at distance from electride
Near Field = sound occurs in close proximity to electrode
36
Describe the path of auditory evoked response from the **electrode to analysis.**
From the electrode, the activity goes through the wire to a preamplifier/amplifier, filters, an analog-to-digital converter, and finally to a computer where it is analyzed and visualized.
Stimulus → Neural activity evoked → transmitted from the auditory structured → through body tissues & fluids → **to surface electrodes → travels through wire → preamplifier/amplifier → filters → analog-to-digital converter → computer where it is analyzed and visualized.**
37
How can we be sure that the response captured is from the auditory central nervous system (CANS) despite the distance of electrodes?
Even though pinpointing the specific source within the CANS can be difficult, the fact that the **stimulus is *sound* confirms that the response originates from within the auditory system.**
38
How long does it take for an AER to occur after the stimulus, and how are these measured?
* It takes about **1 second** for an AER to occur **post stimulus**.
* The AERs are measured in **milliseconds** (1/1000 of a second).
39
How is the region or specific sites within the CANS determined through AERs?
Analyzing the **pattern** of the responses and **calculating** the time *(Latency)* of the occurrence of the AER, it is *possible* to determine the region, and sometimes specific sites, in the CANS generating the response.
40
What are the AER's earliest responses latencies (short,mid or late) and where are they generated?
The earliest responses with the **shortest** latencies in AERs are generated by the **inner ear and auditory nerve.**
41
What does the AER activity occurring a few milliseconds later indicate?
Responses occurring a **few** milliseconds later reflect brainstem activity.
(still short latencies)
* Early response & short latencies = Inner ear and Auditory Nerve (ECochG)
* Few ms Later response = Brainstem (ABR)
* Even Later response = higher structures of CANS, such as cerebral cortex. ( less site specific)
42
Where are the latest AER responses generated?
Responses occurring later reflect activity in the **higher structures of the CANS**, such as the cerebral cortex.
43
Why are neural generators in higher centers of the CANS less site specific?
The higher centers of the CANS are more complex, and involve more neurons making it difficult to pinpoint exactly where the responses are generated.
44
how is the brain activity in AER's measured?
Brain activity that makes up the auditory evoked response is of **very small voltage, measured in microvolts (µV).**
45
what is a microvolt?
A microvolt is one-millionth of a volt or one-thousandth of a millivolt.
46
Why is activity measured from higher regions of the CANS larger in size?
Activity from higher regions like the cerebral cortex is larger because it involves possibly millions of neurons, and the electrodes are closer to the source of activity.
* **involes more neurons**
* **electrodes are closer to the source of activity**
47
# AER
How does neural activity from the brainstem compare to that from higher regions?
Neural activity from the brainstem (ABR) involves fewer neurons and is recorded farther from the source, resulting in smaller measurements compared to activity from higher regions.
48
What are Auditory Evoked Responses (AERs)?
AERs represent electrical activity within the auditory system that is stimulated by sound and can be recorded from various parts, including the inner ear, auditory nerve, and brain regions.
49
What factors are considered when describing AER responses?
When describing AER responses, people usually consider
* where in the auditory system the response originates (like inner ear vs. brain) and
* the timing (latency) of the response in relation to other responses.
50
What is Electrocochleography (ECochG) and what does it detect?
ECochG is used to detect the earliest responses to sound, with components generated in the **inner ear (cochlea)** and the **distal portion of the eighth nerve.**
51
when and where does the Auditory Brainstem Response (ABR) occur?
The ABR comprises components that mostly arise from auditory regions of the **brainstem** and occur **later than ECochG responses.**
52
when & where does the Auditory Middle Latency Response (AMLR) occur?
* The AMLR occurs after the ABR but before later responses, with a timing described as "middle latency," indicating a medium delay.
* (12 - 50 msec)
* thalamus and auditory cortex
53
How are the AERs from ECochG characterized?
ECochG records the **earliest responses**, originating from the **cochlea** and the start of the auditory nerve (**distal eighth nerve**).
54
Describe the origin and timing of ABR responses.
ABR responses from the brainstem and occur a bit later than ECochG responses, reflecting deeper auditory processing.
55
Name the AER types in order of response time.
ECochG - 0 – 1.5 msec
ABR - 1.5 -12 msec
AMLR (mids) - 12 - 50 msec
ALR's (lates) - 50 – 300 msec
P300 (late) - 300+ msec
56
What are Evoked Potentials?
Evoked Potentials are brain responses that occur in reaction to a specific **external stimulus**, such as a sound, light, or touch. These responses can be measured as the brain reacts to the event.
57
What are Non-Evoked Potentials?
Non-Evoked Potentials are brain signals that occur **without** any specific external trigger. They represent the **brain's ongoing activity that is not related to external stimuli**.
58
Which type of electrical brain signals will we primarily encounter?
Evoked Potentials
59
give an example of recording non-evoked responses?
EEG
60
give an example of recording evoked responses?
ECochG
ABR
61
What are auditory evoked potentials, and how are they identified in the presence of ongoing EEG activity?
* Auditory evoked potentials are electrical responses of the nervous system to externally presented stimuli.
* They can be hidden within the larger ongoing electroencephalographic (EEG) activity.
* However, they are identified by *averaging neural responses*. This averaging process reduces components unrelated to the evoked potentials, thus allowing the specific electrical events that occur in response to stimuli to be observed.
62
What are Auditory Evoked Potentials (AEPs)?
AEPs are brain waves or electrical signals produced by the nervous system in response to sound. They represent the brain's response to auditory stimuli.
63
Why are AEPs difficult to observe in an EEG?
Normally, the brain produces a lot of electrical activity constantly, recorded by EEGs. The specific response to sound can be hard to distinguish because it is buried in this ongoing brain noise.
64
What method is used to make AEPs more visible in EEG recordings?
**SIgnal averaging**, where the same sound is played multiple times and the brain's electrical response is recorded each time.
* By averaging these recordings, the **random background activity cancels out, highlighting the consistent response** to the sound.
65
how does signal averaging reveal AEP's in the EEG?
Through signal averaging, components unrelated to the evoked potentials are reduced, allowing the specific electrical events occurring in response to sound stimuli to stand out against the ongoing EEG activity.
66
How are Auditory evoked Potentials classified?
* AEPs can be classified according to whether their **characteristics are determined by external or internal processes (exogenous vs. endogenous)**
* AEPs can be classified according to the time epoch following the stimulus in which they occur.**(latency)**
* AEPs can be classified according to the relation of the recording **electrodes** to the actual generator sites. (Near Field vs. Far Field)
* AEPs can be classified according to what **structures** in the auditory system generates them.
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Responses primarily determined by external auditory stimuli, not requiring conscious perception.
Exogenous AEP
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what is the #2 way AEP's are classified?
"AEPs can be classified according to the time epoch following the stimulus in which they occur. (latency)"
When they happen (Latency):
* AEPs are categorized based on the **timing** of their occurrence after the sound stimulus:
* Very Early: 0 – 1.5 ms (e.g., Cochlear Microphonics (CM), Summating Potential (SP), N1, typically measured in ECochG)
* Early: 1.5 - 12 ms (e.g., Auditory Brainstem Response (ABR))
* Middle: 12 - 50 ms (e.g., Middle Latency Response (MLR))
* Slow: 50 – 300 ms (e.g., Auditory Late Response (ALR))
* P300: 300+ ms (associated with cognitive processing in primary and association areas)
69
what is the #3 way AEP's are classified?
"AEPs can be classified according to the relation of the recording electrodes to the actual generator sites. (Near Field vs. Far Field)"
Where the electrodes are placed (Near Field vs. Far Field):
* Near Field recordings are taken close to where the signals are generated in the body (e.g., intraoperative monitoring on the VIIIth nerve, transtympanic ECochG).
* Far Field recordings are taken from farther away, like from the scalp, and pick up the signals indirectly.
70
what is the #4 way AEP's are classified?
"AEPs can be classified according to what structures in the auditory system generates them."
What part of the auditory system generates them:
* AEPs can be grouped based on the auditory system structure generating them:
* Receptor Potentials: Generated by cochlear hair cells.
* Neurogenic Potentials: Originating from the VIIIth nerve and/or brainstem.
71
AEP's mostly record responses i what field and what are the excpetions?
AEP’s are almost always recorded at **far field** w/ 2 exceptions
1. During **intraoperative monitoring** (when recording electrodes mat be placed directly on the VIIIth Nerve)
2. During **transtympanic membrane ECochG**, (when a recording electrode may be placed on the promontory).
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73
Examples of Exogenous AEPs
Otoacoustic Emissions (OAE), Electrocochleography (ECochG), Auditory Brainstem Response (ABR).
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what are Exogenous AEPs
* Responses primarily determined by **external auditory stimuli**, ***not* requiring conscious perception**.
* Depend on the physical properties of the stimuli; related to the auditory system's direct response to sound.
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Influenced by internal cognitive processes, requiring the listener to perceive and process the auditory signal.
Endogenous AEP's
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Endogenous AEP examples
P300 response, Contingent Negative Variation (CNV), and other long-latency potentials (later than 250 ms).
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what is Endogenous AEPs
* Influenced by **internal cognitive** processes, requiring the **listener to perceive and process** the auditory signal.
* Highly variable and individual, reflecting perceptual and cognitive activities; associated with higher-level brain processing of auditory information.
78
How are Exogenous AEPs characterized?
Exogenous AEPs are determined by **external stimuli** and do **not require** the individual to **consciously** hear the signal. They are typically responses to physical sounds like **clicks** or **tone bursts** and include earlier potentials such as **ECochG and ABR.**
79
How are Endogenous AEPs characterized?
Endogenous AEPs are influenced by **internal cognitive** processes and **require** the individual to **hear and recognize** the signal. These responses include later potentials such as **P300**, which reflect higher-level brain processing.
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What distinguishes Exogenous from Endogenous AEPs in terms of stimulus dependence?
* Exogenous responses are directly **dependent on the physical characteristics** of the eliciting external stimulus, such as sound **intensity** or **type**, while
* Endogenous responses depend on the **individual's cognitive and perceptual processing** of the stimulus.
82
What types of AEPs are considered Exogenous and why?
Earlier auditory evoked potentials like ECochG and ABR are considered Exogenous because they are generated in response to external auditory signals and are independent of the listener's conscious perception.
83
What are some examples of Endogenous AEPs and their significance?
* Endogenous potentials include P300, CNV, and other long-latency responses occurring later than 250 ms.
* These are studied for their role in higher cognitive functions and have variable characteristics dependent on individual perception.
84
What are the latency categories for AEPs?
timing after a sound stimulus:
* Very Early (0 – 1.5 ms), ECochG
* Early (1.5 - 12 ms), ABR
* Middle (12 - 50 ms), MLR
* Slow (50 – 300 ms), ALR
* P300 (300+ ms).
85
In what situations are AEPs recorded at near field?
* Near field recordings occur during **intraoperative monitoring** (directly on the VIIIth Nerve) and
* **transtympanic membrane ECochG** (with an electrode on the promontory).
86
# Exogenous VS Endogenous
don’t need to consciously hear the sound
Exogenous
87
How are AEPs classified based on the generator site?
AEPs are classified by the generator site into
* **Receptor** Potentials, generated by *cochlear hair cells*, and
* **Neurogenic** Potentials, originating from the *VIIIth nerve and/or brainstem*.
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# Exogenous VS Endogenous
must be consciously hearing or recognizing the sound
Endogenous
89
# Near field VS Far-Field
Electrodes are placed close to the part of the nervous system that's generating the signal
Near field
90
# Near field VS Far-Field
Electrodes are placed farther away from the source of the electrical activity.
Far field
91
# Near field VS Far-Field
These are usually used in research or surgical settings, not typical clinical tests.
Near field
92
# Near field VS Far-Field
Common in clinical settings, where electrodes are placed on the ___ or ____
Far field
Common in clinical settings, where electrodes are placed on the **scalp** or **ear canal**
93
# Near field VS Far-Field
Produce smaller signals (lower amplitude).
Far field
94
# Near field VS Far-Field
amplitude stays relatively stable even if you move the electrodes around a bit.
Far field
95
# Near field VS Far-Field
Produce large, strong signals (high amplitude).
Near field
96
# Near field VS Far-Field
signal strength drops off sharply even with small changes in electrode position.
Near field
97
How are AEP's classified according to what structures they generate from?
whether the signals come from sensory receptors or from the nervous system. **Receptor Potentials:**
* Generated by the **cochlear hair cells** (the sensory cells in the inner ear that detect sound).
* These are the very first responses in the hearing process.
* Example: Cochlear microphonic (CM), recorded in ECochG.
**Neurogenic Potentials:**
* Generated by the **auditory nerve** (8th cranial nerve) and/or the brainstem.
* These reflect how the nervous system processes the sound after it’s been detected by the ear.
* Examples: Auditory Brainstem Response (ABR)
98
# AEP classification
generated by the cochlear hair cells
Receptor Potentials
99
# AEP classification
If the signal comes from the ear’s sensory cells, it’s a ___
**receptor potential**
100
# AEP classification
If it comes from the auditory nerve or brain, it’s a
**neurogenic potential.**
101
# AEP classification
Genertaed by the auditory nerve and or brainstem
Neurogenic Potentials
102
# Receptor VS Neurogenic Potentials
Auditory Brainstem Response (ABR)
Neurogenic Potentials
103
# Receptor VS Neurogenic Potentials
Cochlear microphonic (CM), recorded in ECochG.
Receptor Potentials
104
What main Factors affect the Recording and Measurement of AEPs
1. Stimulus Factors
2. Acquisition Factors
3. Non-Pathologic Subject factors
- Gender, Age, etc
4. Waveform Analysis
105
What are the fators that affect the stimulus?
* Stimulus Type
* Stimulus Duration and Rise Time
* Stimulus Polarity
* Stimulus Intensity
* Stimulus Rate
106
What characteristics make a stimulus ideal for generating early latency AEPs like ECochG and ABR?
Early latency AEPs are best elicited with very brief, transient stimuli that have an almost instantaneous onset, such as a **click**, which stimulates a large number of neurons simultaneously.
107
What is a "Click" stimulus and why is it effective for AEP generation?
* A click is characterized by its abrupt onset and broad frequency bandwidth,
* stimulating a broad portion of the cochlear partition simultaneously and eliciting strong responses due to the synchronous action of many neurons.
108
Why are abrupt-onset stimuli more desirable for AEPs?
Abrupt-onset stimuli, like clicks, are more desirable because they elicit responses from a large number of neurons at one time, essential for detecting surface recorded AEPs like ECochG or ABR.
109
What are some alternative stimuli for enhanced frequency specificity in AEPs?
* Filtered clicks
* Clicks with high-pass noise
* Tonebursts
* Tonebursts with high-pass noise
* Tonebursts in notched-noise
* Amplitude modulated (AM) tones
* Frequency-modulated (FM) tones
110
Why are tone bursts with a "2-1-2 envelope" recommended for AEPs?
Tone bursts with a "2-1-2 envelope" (two cycles of rise time, one cycle of plateau, two cycles of decay) balance frequency specificity with neural synchrony, making them effective for eliciting AEPs.
111
How does the stimulus envelope impact the spectral energy of a stimulus?
* The onset and offset characteristics (envelope) of a stimulus affect its spectral energy or frequency characteristics.
* Non-linear envelopes like cosine-squared, **Blackman**, or Hanning functions are preferable for maintaining frequency specificity, as they *minimize spectral spread* into other frequency ranges.
112
Early latency AEPs, such as ECochG and ABR, are best elicited with what?
Early latency AEPs, such as ECochG and ABR, are best elicited with **very brief, transient stimuli that have an almost instantaneous onset. (Click)**
113
The more neurons that discharge within a very brief time, the what?
The more neurons that discharge within a very brief time, the **larger the amplitude of the recorded peaks.**
114
Evoked responses directly depend on ____ of neuronal activity.
Evoked responses directly depend on **temporal synchronization** of neuronal activity.
115
Shorter stimuli, like ____ , are ____ and better at eliciting _____ due to their abrupt onset and brief duration.
Shorter stimuli, like **clicks**, are **less frequency specific** and better at eliciting **synchronous neural responses** due to their abrupt onset and brief duration.
116
the longer the duration of a stimulus, the _____ the stimulus will be.
the longer the duration of a stimulus, the **more frequency specific** the stimulus will be. (Pure tone)
117
A 100-microsecond pulse on a standard earphone generates a broad-band signal (click) with primary frequency emphasis determined by what?
A 100-microsecond pulse on a standard earphone generates a broad-band signal (click) with primary frequency emphasis determined by **the earphone’s resonant frequency.**
118
For a Click…….The greatest agreement with pure-tone thresholds is in the ____ to ____ frequency range
For a Click…….The greatest agreement with pure-tone thresholds is in the **2000 to 4000Hz** frequency range
119
A linear rise and fall of energy is characterized by an
**abrupt change** from *no stimulus to the rise* of energy and a **sharp change** when the *plateau is reached.*
120
If an envelop is used that has more gradual onset and offset function, such as a cosine-squared, ____, or Hanning function, then there is less ____, of energy into other frequency ranges.
If an envelop is used that has more gradual onset and offset function, such as a cosine-squared, **Blackman**, or Hanning function, then there is **less spectral spread** of energy into other frequency ranges.
121
What is stimulus polarity?
Polarity refers to the direction the wave moves when it first starts, measured at the surface of the transducer.
122
What is Condensation Polarity?
Condensation Polarity, the initial movement of the pressure wave is **toward** the eardrum, causing the air molecules to push the *stapes footplate into the oval window*, resulting in **slightly longer latencies** due to the need for the stapes footplate to move back before stimulation can occur.
123
What is Rarefaction Polarity?
Rarefaction Polarity involves the initial movement of the wave **away** from the **tympanic membrane**, leading to an *outward movement of the stapes* footplate from the oval window. This type of stimulus has *shorter latencies* as it *starts immediately* upon delivery.
124
How do stimulus duration and frequency emphasis affect AEP generation?
a 100 - microsecond pulse (click) from a insert generates a broadband signal with frequency emphasis typicallyin the 1000 to 4000 hz rnage aligns well with pure tone thresholds in the 2000 to 4000 hz frequency range
125
What is Alternating Polarity and its cons in testing.
Alternating Polairty is when the direction of the sound wave **alternates between moving away from and towards ** the TM with each trial.
* it is *not reccommended for air-conduction ABR* testing due to potential cancellation of out of -phase responses
* is *used in ECochG* to ensure cleaner responses provided ANSD has been ruled out.
126
How do Rarefaction stimuli impact AEP measurement
Rarefraction stimuli typically result in shorter latencies and higher amplitude for the early components of the AEP due to more efficient activation of hair cells, as they cause an outward movement of the earphone diaphragm and stapes.
127
How do Condensation stimuli impact AEP measurements?
Condensation stimuli may cause slightly longer latencies in early AEP responses compared to rarefaction stimuli, but Wave V amplitude tends to be larger, which is useful for estimating hearing levels.
128
Why might you start with either a condensation or rarefaction stimulus rather than alternating polarity when testing?
Starting with a condensation or rarefaction stimulus is needed to rule out ANSD.
* alternating polarity could result in a flat line in ANSD cases, and without ruling out ANSD could result in an incorrect diagnosis.
129
What are the advantages of using Rarefaction polarity in AEP testing?
Rarefaction polarity is advantageous because it typically produces upward movement of the basilar membrane and depolarization of hair cells, resulting in **shorter latencies** and **higher amplitudes**of AEP, which aids efficient data acquisition and analys
130
What are the potential drawbacks of using Condensation polarity in AEP testing?
Condensation polarity can result in *larger Wave V amplitudes*, useful for hearing level estimation, it may also lead to **slightly longer latencies** in the early components of AEP due to its initial inward movement of the diaphragm and subsequent outward movement.
131
How does Alternating polarity reduce stimulus artifact in AEP testing?
Alternating polarity is used at **high intensities** to reduce stimulus artifact by **averaging** out the effects of condensation and rarefaction, leading to *clearer* and more *reliable* AEP measurements, particularly useful in Electrocochleography (ECochG).
132
Why is Alternating polarity not recommended for air-conduction ABR testing?
Alternating polarity is not recommended for air-conduction ABR testing because it could lead to the cancellation of out-of-phase responses, potentially resulting in spuriously abnormal recordings.
133
What is the practical application of Alternating polarity in clinical settings?
* Alternating polarity is *routinely used in ECochG* to ensure cleaner responses.
* It is particularly valuable once Auditory Neuropathy Spectrum Disorder (ANSD) has been ruled out, to avoid misleading results
134
How does increasing Stimulus intensity affect AEP waves?
Stimulus *intensity* **increases**, wave *latencies* **decrase** (shorter/faster) and *amplitude* **increases** (larger)
135
How does decreasing stimulus intesnity affect AEP waves?
stimulus *intensity* **decreases**, waves *latencies* **increase** (longer and slower) and *amplitude* **decreases** (smaller)
136
What is the unit measure for stimulus intensity in AEP's?
The unit of measure is the decibel (dB).
137
what are all of the different measumrent units that can be used for Stimulus Intensity?
* dB SPL (Sound Pressure Level)
* dB peSPL (Peak-equivalent SPL)
* dB HL (Hearing Level)
* dB SL (Sensation Level
* dB nHL (Normal Hearing Level) -ABR
138
the actual intensity level and frequency information reaching the cochlea are dependent on what?
* the acoustic properties of the **transducer**
* the volume (size) of the **ear canal**, and
* middle ear transmission characteristics
139
What could be the result if the ISI is too short?
The result may be alteration of the response such as:
**increased latency or
decreased amplitude**
140
How does the stimulus rate affect the latency and amplitude of AEP components?
The rate at which auditory stimuli are presented affects both the latency (timing) and amplitude (size) of the AEP components. Generally, at rates higher than approximately 30 stimuli per second, latencies increase and amplitudes of earlier components decrease.
Becuase higher than 30 stim may not alow enough neuron recovery time.
141
The rate at which auditory stimuli are presented affects both the ____and ____of the AEP components.
The rate at which auditory stimuli are presented affects both the **latency** (timing) and **amplitude** (size) of the AEP components.
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the time interval between successive stimulus presentations.
Interstimulus Interval (ISI)
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What is interstimulus Interval (ISI)
ISI is the time between each stimulus being played.
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Why is ISI Important?
ISI is critical in determining the effectiveness of the stimulus in eliciting a neural response.
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How do you calculate the ISI for a given stimulus rate?
dividing the total time period (e.g., one second) by the number of stimuli. **1 sec/rate = ISI**
* ex: at a stimulus rate of 20 per second, the ISI is 50 milliseconds (1/20 = 0.05 seconds, 0.05 x 1000 = 50 milliseconds).
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What is the ISI needed for AEPs like ECochG or ABR
For AEPs that occur quickly, such as ECochG or ABR (within about 5-6 milliseconds), **short ISIs are required.** This **allows for more rapid stimulus rates without overlapping the neural recovery time.**
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What happens if the ISI is shorter than the refractory period?
If the ISI is too short, it may lead to **incomplete neural recovery**, affecting the response by **increasing latency** or **decreasing amplitude**.
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What are the Pros and cons of adjusting the ISI and stimulus rate in clinical AEP testing?
* Adjusting the ISI and stimulus rate can **optimize the accuracy and effectiveness **of AEP testing.
* Careful selection of these parameters is essential to ensure that each stimulus contributes effectively to the response without being masked by the refractory period of the neuron.
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What happens of the ISI time exceed the refractory period?
If the ISI time period exceeds the refractory period, then the neural unit can **fully recover** and will be **responsive to the next stimulus**.
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If the ISI is too short (shorter than the refractory period), it may lead to what?
If the ISI is too short (shorter than the refractory period), it may lead to **incomplete neural recovery,** affecting the response by **increasing latency or decreasing amplitude.**
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If the ISI time period exceeds the refractory period, then the
If the ISI time period exceeds the refractory period, then the neural unit can **fully recover** and will be **responsive to the next stimulus.**
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What transducer should be used for AEP's
Inserts always unless extenuating cirumstanaces
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What is the benefit insert earphones for AEP testing?
* 0.9ms delay
* Prevent ear canal collapse
* Better IA
* Reduce enviormental noise = clearesr test results
154
What is the benefit of the 0.9-ms delay line in insert earphones for AEP testing?
The 0.9-ms delay line in insert earphones helps separate the stimulus artifact from the onset of the response, making Wave I of the Auditory Brainstem Response (ABR) more visible.
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How does using insert earphones affect Wave I amplitude in AEP measurements?
The use of insert earphones typically results in a lower amplitude of Wave I compared to supra-aural earphones, partly due to more effective stimulus artifact separation.
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Why is the Wave V-to-Wave I amplitude ratio important in AEP analysis?
The Wave V-to-Wave I amplitude ratio is an important diagnostic metric in AEP analysis, and the type of earphones used affects this ratio due to differences in Wave I amplitude.
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What should be specified when reporting AEP results?
specify the **type of earphones** used when reporting AEP results, especially if amplitudes are measured, as this impacts the interpretation of auditory responses.
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What is the fucntion of the electrode?
The electrode is the ssensing device
* detect the brain’s bioelectrical activity and send it to the pre-amplifier.
* uses a specialized metal plate where electrical stimluli are measured or applied to the body
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Where are the AER's electrodes placed?
scalp, mastoid, earlobes, ear canal, or eardrum (TM).
these are common ones there are several types
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WHat is the overall goal in selecting electrode type and placement?
The goal is to choose the type and placement that **gives clear, strong, and complete evoked responses.**
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What can electrode effects alter?
Electrodes can affect the AEP’s:
* **Latency** (timing)
* **Amplitude** (size)
* **Morphology** (shape)
* **Polarity** (direction)
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Disc-Type Electrode
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Disposable Electrode
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# True or False
Electrode effects depend on the complex interaction between electrode location and location of neural generators of the responses
TRUE
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What are the most common electrode types used in AER measurments?
The **disc** or cup **electrode**
The **disposable electrode**
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Name other types of electrodes we will use in class for AER that are not disc or disposiable?
1. The earclip electrode (ABR)
2. The canal (tiptrode/tymptrode) electrode for ECochG
* ER insert w/ gold foil
* Wire electrode wrapped in silastic tubing w/ gel
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It is best to use electrodes made of same metal in one recording in order to what?
To avoid imbalances caused by different electrical properties of different metal compositions of electrodes
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What electrode is commmonly used in infants?
Disposable Electrodes
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Disposable Electrodes
Advantages
* Cann apply to skin without application of conducting gel, paste, or cream
* No tapes required to adhere to skin
* Contributes to infection control
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Disposable Electrodes disadvantages
Replacement costs
Limited selection of materials
Limitations of design (no ear clip style)
They have an expiration date and should not be used past the expiration date!
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Electrode ---- and ---- can impact the AEP’s latency, amplitude, morphology, and polarity.
Electrode **type** and **placement** can impact the AEP’s latency, amplitude, morphology, and polarity.
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What is the location and characteristic of a Non-inverting Electrode in auditory testing?
* The Non-inverting Electrode is typically located at **Cz or the midline forehead near Fz. **
* The polarity of the signal from this electrode is **not inverted,** meaning it **retains the original signal characteristics.**
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What is the location and characteristic of an Inverting Electrode in auditory testing?
* The Inverting Electrode is placed on the **earlobe or mastoid** of the stimulus side (A1 or A2).
* The polarity of the signal from this electrode is (inverted) **flipped 180 degrees**, which means it reverses the electrical phase of the signal.
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# True or False
Notch filters are commonly used in AER recordings
FALSE
Notch filters are typically **not** used in AER recordings
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# Name the filter
Low pass
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# Name the filter
High pass
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Name the filter
Band-pass filters
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Name the filter
Band-reject or notch filters
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Name the filter
**Low pass**
Low-pass filter: Lets low frequencies through, blocks high frequencies
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Name the filter
**High pass** High-pass filter: Lets high frequencies through, blocks low frequencies
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Name the filter
**Band-pass filter:** Lets a range of middle frequencies through, blocks very low and very high ones
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Name the filter
**Band-reject or notch filters**
Band-reject (notch) filter: Blocks a specific frequency range, lets others through (opposite of band-pass)
Notch filters are usually not used in AER testing
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What is the function of filters for AEP testing?
* Filters selectively remove unwanted parts of the signal.
* Eliminating both internal and external noise
* enhacing the clarity and accuarcy of the evoked responses
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Filtering of the physiological response is used to what?
* Remove **internal noise **(like muscle or brain activity not related to the AEP)
* Block **external noise** (like 60 Hz from electrical equipment) (enviormental)
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# true or false
when internal noise filtering is done correctly all internal noise is removed from the signal.
FALSE
Neuromuscular noise is in the 100-500 Hz region (cannot be filtered out entirely) but may also include frequencies of up to 5000 Hz.
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High pass filters
High-Pass Filters: Block lower-frequency energy and allow higher-frequency energy to pass.
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Low pass filters
Block higher-frequency energy and allow lower-frequency energy to pass
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Band - pass filters
* Allows frequencies below a certain cutoff frequency and above a certain cutoff frequency
* Commonly used in AEP to focus on the frequency range where AEP components are expected.
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Band-Reject (Notch) Filters:
Rejects very specific frequencies between a low and high cutoff frequency, opposite of band-pass filters
**Notch filters are typically *not* used in AER recordings**
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---- is another technique used to enhance signal detection in the presence of electrical activity
Filtering
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what is filter slope
* A filter cuts off the signal at the specified cutoff frequency
* This cutoff does not happen abruptly but rather at a given slope, which is typically **how fast or slow the gain measured in decibels (dB) is reduced**
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Attenuation of filter slopes is quantified what
Attenuation of filter slopes is quantified in **decibels per octave**
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WHy are filter slopes important?
The slope can affect how **clear** or **accurate** the AER waves are, especially for **mid and late responses.**
* Steep filter slopes (e.g., 24 dB per octave) where the gain reduction is rapid, can produce artifacts in AER recordings
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why is the right choice of filter important for recording AEP's?
Because ...
* Too **much** filtering can **eliminate the AER response**
* Too **little** filtering can lead to **high noise levels and poor AER recordings**
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what is the most commonly used filter for AER recordings?
band-pass filters are commonly used
and are generally the best filter to use
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Too much filtering can what?
Too much filtering can **remove some of the actual response and can be misleading**
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Too little filtering allows for what?
Too little filtering allows **excessive artifact to contaminate the waveform**
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Incorrect filtering can casue what?
* distortion
* affect latency
* too much = remove actual response
* Too little = lots of artifact
* Consistency of filter settings is important to ensure reliable comparisons across wave form recordings
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what does an amplifier do?
amplifier increases/boosts the strength of an electrical or acoutsic signal.
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Why is amplification needed?
* AEP signals from the cochlea or auditory nerve (VIIIth nerve) are very tiny—about 1 microvolt (µV).
* The average size of Wave V in ABR is about 0.5 µV, so amplification is needed to clearly see the response.
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what two characteristics have direct influence on successful AER recordings?
Input Impedance
Common mode Rejection (CMR)
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What is input impedance?
**Impedance is resistance to electrical current.** across the amplifer input (electrodes)
203
When running impedance what do you want your electrodes to be at?
you want your electrodes to be **3-5 kohms or less**
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For AER recodings optimally the input impedance of the amplifier should be what?
the input impedance of the **amplifier** should **equal or** be **higher** than **electrode impedance**
* Amplifer need to be equal to higher to electride impednace
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how and when do problems occur in refrence to Input impedance
recording problems occur with imbalance (asymmetry) between interelectrode impedance or high impedance for each electrode
206
how is the tiny AER detected in the midst of electrical activity (EEG) that is of far greater amplitude?
Common Mode Rejection (CMR) allows the electrodes to pick up what is common to each electrode (noise) and cancel it out
* It works by canceling out noise that is the same at both electrodes (like electrical interference).
* For example, if two electrodes (e.g., on the forehead and earlobe) both pick up the same outside noise, that noise gets removed.
* But the AER signal, which is different at each site, is kept.
* This helps make the evoked response clearer.
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What is the differential amplifier?
The differential amplifier is part of the system that helps with CMR (Common Mode Rejection).
* It reverses polarity (+ve or -ve) of the inverting electrode’s input voltage and adds it to the non-inverting electrode
* The same activity in each electrode is eliminated
* electrical interference is removed, and what's left is the signal of interest.
208
what happens if two electrods are placed next to each other on the same location and why?
* the result would be nearly a flat line
* becuase the signals are too similar and get canceled out by CMR.
208
Using electrodes on different areas (like vertex and earlobe) helps:
* **Reduce noise**
* Sometimes **increase wave amplitude**
* But this doesn’t help much with early waves, like Wave I of the ABR, which is often very important in clinical testing.
208
What is artifact rejection
Artifact rejection refers to the process of **eliminating non-AEP signals** from the recording to **ensure a clean and accurate waveform**
209
what are artifacts
Artifacts are electrical activities not related to the auditory response and should be excluded from the final AEP analysis.
210
# True or False
At the stage of artifact rejection it has not been filtered, amplifed or cleaned. This is the first stage.
FALSE
the input has been exposed to CMR and amplification
211
what are the sources of artifacts?
* **Electrical** – Noise from the equipment or wires in the recording system
* **Electromagnetic** – Noise from external or non-patient source, like an X-ray view box, phone, or computer near the test area
* **Electrophysiologic** – Internal Noise from the patient’s body, like muscle movements or tensing, especially from the post-auricular muscle (PAM) behind the ear
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what are the three main approaches to reducing the negative influence of artifacts on the ABR
**Remove the source of the artifact**
* Turn off interfering things like the X-ray view box, phone, or computer
* Ask the patient to relax or sleep
* Use a dedicated electrical circuit for AER testing
**Modify test settings**
* Increase intensity, change filters, increase # sweeps, etc
**Adjust artifact rejection**
* The system is set to ignore any signal that goes above a certain voltage
* Those signals are not included in the averaging process, helping to keep the response clean
213
Artifact rejection helps remove what?
Artifact rejection helps remove very **large signals that clearly aren’t part of the ABR.**
* ABR signals are very small—about 0.5 microvolts, so anything like 1 or 2 volts is obviously not ABR and should be ignored.
214
Artifact Rejection cons
Artifact rejection is helpful, but it can’t fix everything.
* If the patient or environment is causing constant noise and it’s not addressed, the system will keep rejecting signals and testing will t**ake much longer.**
* Newer systems, like those used in newborn hearing screenings or during surgery, have advanced artifact rejection features.
But places like nurseries and operating rooms have lots of machines that cause noise—and many of them can’t be turned off because they’re important for the patient’s care.
215
how can artifact rejection help with when a sweep occurs that contains excessive voltage amplitudes, excessive noise is included in the signal average?
Artifact rejection excludes these excessive voltages or amplitudes
* any sweep with voltage too high is ignored and not included in the average
216
how does common mode rejection work?
* When two electrodes are placed in different spots—like the vertex (Cz) and earlobe (A1 or A2)—they **both pick up the same noise** from the environment. This noise is the common because it's the same at both places.
* The **differential amplifier** **flips** the signal from the inverting electrode (A1/A2) and *adds* it to the non-inverting electrode (Cz). This works like *subtracting* one from the other, which **removes the shared noise**.
* If both electrodes picked up exactly the same AER, the signal would **cancel** out too, and you'd get a flat line.
But since Cz and A1/A2 detect different parts of the AER, subtracting them:
* Removes the shared noise
* Keeps the AER
* Sometimes even increases the size of certain ABR waves
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In short what does the differential amplifier do?
A differential amplifier flips and subtracts the signals from each electrode
218
# CMR
Since the noise is the same at both electrodes, when the system subtracts Cz – A1, the --- ---- is ------ out, and what's left is mostly the --- --- ---
Since the noise is the same at both electrodes, when the system subtracts Cz – A1, the **shared noise** is **canceled** out, and what's left is mostly the **actual auditory response**.
219
Signal Averging converts the what?
* The signal averager converts the analog electrical activity from the amplifiers into digital values
* These digital values are then processed bu the computer to add or average
220
how does the time period work for signal averaging?
The time window (when the response is expected) tells the system how long to collect data:
* About 10–15 ms for ABR
* About 2–5 ms for ECochG
* The time window is divided into small parts called time bins or data points.
* The brain’s response to sound happens at the same time points after each sound.
* **As the *sound is repeated*, the same signals build up in the same bins—positive in some, negative in others—creating the waveform we recognize as the AEP. (taking the average of all the responses)**
* Will do about 3 to 5 hundred sweep the more noise the more sweeps youll want to do
221
how does CMR and Signal Averaging work together?
The response and noise are shown at the vertex electrode (top).
* The use of CMR allows subtraction of the (cancels out shared noise) response at the ear from the vertex response (inversion)
* Resulting in reduced noise.
* With signal averaging (shown at the bottom), the noise is further reduced so that the desired response can be seen.
222
Signal averaging is one technique used to ---- the size of the AER and ----- the size of the noise (other electrical activity) improving -----
Signal averaging is one technique used to **increase** the size of the AER and **reduce** the size of the noise (other electrical activity) improving **signal-to-noise ratio (SNR)**
223
____ makes AER measurements clinically possible
**Signal averaging** makes AER measurements clinically possible
224
describe how signal averaging works
* The time window is divided into small intervals called time bins or data points.
* The auditory response occurs at consistent time points after each sound.
* When the same stimulus is presented repeatedly:
* The AER is consistently time-locked and adds up at the same bins.
* The noise, being random, cancels itself out over time.
* **takes and average off all the sweeps to = a wave the more sweeps = better waveform resolution**
225
A trigger pulse is used to what?
A trigger pulse is used to mark the **start of the brainwave recording window** (called the recording epoch).
226
In order to pick out a brainwave (evoked response) from all the background brain noise, the system needs to know what?
In order to pick out a brainwave (evoked response) from all the background brain noise, the system needs to know **exactly when the sound (stimulus) was presented**.
