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Electrophysiology > Intro > Flashcards

Intro Flashcards

1
Q

auditory evoked potentials (AEPs) definition

A
  • electrophysiologic responses that arise from one or more places within the peripheral and/or central auditory system.
  • a response to acoustic stimuli
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2
Q

AEPs are recorded from specific places such as?

A

scalp, on the ears, within the ears

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3
Q

AEPs appear as what onscreen?

A

waveforms, with positive and negative waves (components) at certain times after presentation of stimuli

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4
Q

What provides amplitude information on a waveform?

A

height/depth of a peak

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5
Q

What provides latency information on a waveform?

A

a peak’s time of appearance

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6
Q

If an AEP can follow/phase-lock to a repetitive pattern in a stimulus, how is it usually analyzed?

A

in the frequency domain

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7
Q

What are the 3 main ways AEPs are classified?

A
  • latency
  • anatomical site of generation
  • relationship to the stimulus
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8
Q

Latency descriptors for AEPs

A
  • short (<15 msec)
  • middle (15-80 msec)
  • long (>80 msec)
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9
Q

Exogenous potential definition

A
  • A sensory evoked potential typically elicited and subsequently affected by physical parameters of the stimulus (intensity, frequency, duration).
  • ex: ABR
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10
Q

Endogenous potential definition

A
  • a potential less influenced by stimulus’ physical parameters, and rather the contextual factors of the stimulus.
  • exhibit very long latencies
  • arise from demands on psychological processes (attention, memory) to a particular event, like listening to a rare stimulus in sequence of a repetitive stimulus
  • ex: P300
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11
Q

What items are included in typical instrumentation for electrophysiology?

A
  • computer
  • amplifier box
  • electrode box
  • electrodes
  • transducers
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12
Q

Sampling of a digital signal involves what?

A

Breaking up a continuous signal into a limited number of manageable units (ex: recording ABR for 10 msec with 256 sampling points)

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13
Q

Time domain analysis definition

A
  • evaluates the amplitude of signal over time
  • signal appears as a waveform with alternating positive and negative values
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14
Q

Frequency domain analysis (spectrum) definition

A
  • removes time to reveal the spectral energies of the signal as the waveform is translated to its respective amplitude values across frequencies
  • ASSR is usually analyzed this way
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15
Q

What are the typical stimuli generated for electrophysiologic testing?

A
  • clicks
  • tone bursts
  • speech
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16
Q

What are some acquisition parameters used in electrophysiology?

A
  • differential amplification
  • filtering
  • signal averaging
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17
Q

Acquisition parameters are used for what?

A
  • to extract the smaller AEP signal and to attenuate noise
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18
Q

What is the purpose of amplification?

A
  • to reduce background noise through differential recording
  • to bring the signal of interest to the forefront
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19
Q

How many electrodes are required for a basic differential recording?

A

a minimum of 3 electrodes (non-inverting, inverting, and ground)

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20
Q

What is common-mode rejection?

A

the cancelling of signals common to both inputs

21
Q

Filtering is used for what?

A
  • to improve the SNR by suppressing noise not in the frequency bands associated with the AEP
  • essentially, to pass signals of interest while rejecting noise
22
Q

What is the Fast Fournier Transform?

A

an algorithm that breaks down the AEP into its component frequencies

23
Q

What are the types of filters?

A
  • high pass
  • low pass
  • bandpass
  • notch (band-reject)
24
Q

Signal averaging definition

A
  • noise is NOT time-locked to the stimulus, so it cancels itself out
  • time-locked signals sum together, further pushing them to the forefront
25
Q

Electrodes form the … … between the patient and the AEP recording.

A

primary connection

26
Q

Electrode impedance definition

A

the electrical opposition determined by: electrode’s surface area, the tissue it’s attached to, and type of metal

27
Q

What impedance value is ideal for AEP recording?

A

no more than 5 kiloohms

28
Q

What is the 10-20 system of electrode placement (Jasper)?

A
  • electrodes are manually placed following measurement from standard positions on the scalp
  • each electrode is given a designation based on brain area and a subscript letter or number to indicate midline or homologous areas of the left and right hemispheres
29
Q

What is an advantage of the 10-20 system of electrode placement?

A

it can accommodate various head sizes and shapes due to its proportional measurements for electrode placement

30
Q

What are the designated brain areas for the 10-20 electrode system?

A
  • frontal (F)
  • parietal (P)
  • occipital (O)
  • temporal (T)
  • central (C)
31
Q

10-20 electrode placement specifications:

A
  • even #s = right hemisphere
  • odd #s = left hemisphere
  • midline electrodes are labeled with a “Z” (zero)
32
Q

What other electrodes are included in the 10-20 placement system?

A
  • frontal pole (Fpz)
  • earlobes (A1 and A2)
  • cerebellar (Cb1 and Cb2)
  • mastoids (M1 and M2)
  • ipsilateral lobe (Ai)
  • contralateral lobe (Ac)
  • nape of the neck (C7)
33
Q

What influences how electrodes are arranged for recording?

A

the A&P behind the AEP of interest

34
Q

What influences how many channels for recording are needed?

A
  • the AEP of interest
  • the reason for testing
35
Q

What defines the time window in recording?

A

the amount of time that will be analyzed in the recording (it should be sufficiently long to capture the entire AEP)

36
Q

Sampling rate definition

A
  • the recorded number of samples of a sound taken per second (represents the event digitally)
37
Q

The number of sweeps is also known as?

A

the # of stimulus repetitions during recording

38
Q

The number of sweeps needed for an average AEP is inversely proportional to what?

A
  • the SNR, and the amplitude of the AEP of interest
  • good SNR = can stop averaging
  • poor SNR = more sweeps needed
39
Q

The stimulation rate during recording is dependent on what?

A

the time window for the recording (because the goal during AEP testing is to present only one stimulus per time window)

40
Q

Filter settings for recording are used for what?

A

to eliminate spectral energy not contained within the AEP of interest (goal is to maximize the SNR of the recording)

41
Q

What general factors should be taken into account when recording AEPs?

A
  • age of the patient (think about CANS maturity)
  • gender (women vs. men)
  • muscle activity (for most tests, except VEMPs, we want to record neuronal activity, not myogenic activity)
  • attention (not a factor except for the P300)
  • temperature (hypothermia can prolong latencies)
42
Q

What information do we typically learn from normative data?

A
  • the mean (central tendency) of a group
  • the standard deviation (variability) of a group
43
Q

What two main measurements can obtained and interpreted during electrophys. recording?

A

latency and amplitude

44
Q

What are the 2 absolute latencies that can be recorded?

A
  • inter peak latency (time between successive peaks)
  • intramural latencies (compares each ear)
45
Q

Amplitude on a waveform can be identified as…?

A

vertical, and peak to peak

46
Q

What highly influences a patient’s latency and amplitude values in their recording?

A

the overall signal-to-noise ratio

47
Q

When is filtering of a signal decided upon for recording?

A

it’s either predetermined or set prior to obtaining all recordings to restrict only certain frequencies

48
Q

Aggressive filtering can lead to what?

A

Waveform distortions, such as amplitude reduction or latency shifts

49
Q

Smoothing of a recording involves what?

A

clumping together several adjacent samples of the signal and forcing them into a common value (this is done throughout the entire waveform)

Electrophysiology (5 decks)

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