Intro Flashcards
auditory evoked potentials (AEPs) definition
- electrophysiologic responses that arise from one or more places within the peripheral and/or central auditory system.
- a response to acoustic stimuli
AEPs are recorded from specific places such as?
scalp, on the ears, within the ears
AEPs appear as what onscreen?
waveforms, with positive and negative waves (components) at certain times after presentation of stimuli
What provides amplitude information on a waveform?
height/depth of a peak
What provides latency information on a waveform?
a peak’s time of appearance
If an AEP can follow/phase-lock to a repetitive pattern in a stimulus, how is it usually analyzed?
in the frequency domain
What are the 3 main ways AEPs are classified?
- latency
- anatomical site of generation
- relationship to the stimulus
Latency descriptors for AEPs
- short (<15 msec)
- middle (15-80 msec)
- long (>80 msec)
Exogenous potential definition
- A sensory evoked potential typically elicited and subsequently affected by physical parameters of the stimulus (intensity, frequency, duration).
- ex: ABR
Endogenous potential definition
- 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
What items are included in typical instrumentation for electrophysiology?
- computer
- amplifier box
- electrode box
- electrodes
- transducers
Sampling of a digital signal involves what?
Breaking up a continuous signal into a limited number of manageable units (ex: recording ABR for 10 msec with 256 sampling points)
Time domain analysis definition
- evaluates the amplitude of signal over time
- signal appears as a waveform with alternating positive and negative values
Frequency domain analysis (spectrum) definition
- 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
What are the typical stimuli generated for electrophysiologic testing?
- clicks
- tone bursts
- speech
What are some acquisition parameters used in electrophysiology?
- differential amplification
- filtering
- signal averaging
Acquisition parameters are used for what?
- to extract the smaller AEP signal and to attenuate noise
What is the purpose of amplification?
- to reduce background noise through differential recording
- to bring the signal of interest to the forefront
How many electrodes are required for a basic differential recording?
a minimum of 3 electrodes (non-inverting, inverting, and ground)
What is common-mode rejection?
the cancelling of signals common to both inputs
Filtering is used for what?
- 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
What is the Fast Fournier Transform?
an algorithm that breaks down the AEP into its component frequencies
What are the types of filters?
- high pass
- low pass
- bandpass
- notch (band-reject)
Signal averaging definition
- noise is NOT time-locked to the stimulus, so it cancels itself out
- time-locked signals sum together, further pushing them to the forefront
Electrodes form the … … between the patient and the AEP recording.
primary connection
Electrode impedance definition
the electrical opposition determined by: electrode’s surface area, the tissue it’s attached to, and type of metal
What impedance value is ideal for AEP recording?
no more than 5 kiloohms
What is the 10-20 system of electrode placement (Jasper)?
- 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
What is an advantage of the 10-20 system of electrode placement?
it can accommodate various head sizes and shapes due to its proportional measurements for electrode placement
What are the designated brain areas for the 10-20 electrode system?
- frontal (F)
- parietal (P)
- occipital (O)
- temporal (T)
- central (C)
10-20 electrode placement specifications:
- even #s = right hemisphere
- odd #s = left hemisphere
- midline electrodes are labeled with a “Z” (zero)
What other electrodes are included in the 10-20 placement system?
- 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)
What influences how electrodes are arranged for recording?
the A&P behind the AEP of interest
What influences how many channels for recording are needed?
- the AEP of interest
- the reason for testing
What defines the time window in recording?
the amount of time that will be analyzed in the recording (it should be sufficiently long to capture the entire AEP)
Sampling rate definition
- the recorded number of samples of a sound taken per second (represents the event digitally)
The number of sweeps is also known as?
the # of stimulus repetitions during recording
The number of sweeps needed for an average AEP is inversely proportional to what?
- the SNR, and the amplitude of the AEP of interest
- good SNR = can stop averaging
- poor SNR = more sweeps needed
The stimulation rate during recording is dependent on what?
the time window for the recording (because the goal during AEP testing is to present only one stimulus per time window)
Filter settings for recording are used for what?
to eliminate spectral energy not contained within the AEP of interest (goal is to maximize the SNR of the recording)
What general factors should be taken into account when recording AEPs?
- 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)
What information do we typically learn from normative data?
- the mean (central tendency) of a group
- the standard deviation (variability) of a group
What two main measurements can obtained and interpreted during electrophys. recording?
latency and amplitude
What are the 2 absolute latencies that can be recorded?
- inter peak latency (time between successive peaks)
- intramural latencies (compares each ear)
Amplitude on a waveform can be identified as…?
vertical, and peak to peak
What highly influences a patient’s latency and amplitude values in their recording?
the overall signal-to-noise ratio
When is filtering of a signal decided upon for recording?
it’s either predetermined or set prior to obtaining all recordings to restrict only certain frequencies
Aggressive filtering can lead to what?
Waveform distortions, such as amplitude reduction or latency shifts
Smoothing of a recording involves what?
clumping together several adjacent samples of the signal and forcing them into a common value (this is done throughout the entire waveform)
