midterm Flashcards
describe the amplitudes of a response in correlations with latencies
the shorter the latency, the smaller the amplitude.
describe how the frequency spectrum is related to latency
the shorter the latency the higher the frequency spectrum
how does stimulation rate relate to latency
the shorter the latency, the faster the stimulus rate.
does this mean: the faster the stimulation rate the shorter the latency?
how are latency and variability relate?
the shorter the latency, the smaller the variability
how does electrode position relate to latency?
small shifts in electrode location can alter waveform morphology. the shorter the latency, the more far-field the response.
what does far-field response mean?
how susceptible is a response to a “state” change?
the shorter the latency, the less susceptible to changes in the subject’s state.
describe the rate of maturation in relation to latency
the shorter the latency, the more rapidly maturation proceeds
what the fuck does this mean?
name the 4 stimulus factors used when recording bioelectrical fields
- earphones
- type (tonegs, clicks, speech)
- intensity
- stimulation rate
name 2 subject factors when recording bioelectric fields
- age
- awake or asleep state
name 5 main recording factors when recording bioelectric fields
- Electrodes (impedance, montages)
- Differential Amplification
- A - D conversion (amplitude resolution, sampling rate, time base)
- Averaging
- Filtering (high pass, low pass, slope)
what is a major challenge in ABR?
maximizing the detection of the signal!
a sound-evoked electrical signal is small/extraneous biologic and environmental noise is high
One of the recording factors in recording bioelectric field is electrodes. name some variations in the electrodes that can make a difference.
impedance
montages
-what is ‘montages’?
One of the recording factors in recording bioelectric field is A-D conversion. name some variations in A-D conversions that can make a difference
- amplitude resolution
- sampling rate
- time base
One of the recording factors in recording bioelectric field is filtering. name some filtering variations
- high pass
- low pass
- slope
What does latency mean?
point in time relative to stimulus onset
what does trigger mean?
beginning of time window. signals averager to enable alignment of all stimulus presentation sweeps
what is a pre-stimulus interval?
the period between trigger and stimulus.
-enables assessment of non-stimulus-related brain activity.
what is rate? (in terms of a stimulus)
the number of stimulus repetitions per second
what is ISI?
interstimulus interval
-time from offset of one stimulus to onset of the next
what is SOA?
stimulus onset asynchrony
-time from onset of one stimulus to onset of the next
what is stimulus measured in?
level or intensity. its measured in dB SPL or dB nHL
dB nHL: referenced to normal threshold for that particular stimulus
dB SPL: usually measured as peak SPL
what is the goal of ABR (in terms of stimulus)?
to collect the responses as quickly as possible to minimize test time
-you are limited by the fact that the repetition rate must be slow enough to eliminate the adaptation of the response you are recording
does stimulus rate matter? why?
Rate matters. Once the rate is super fast (ex 66.6/sec). If your pt has some kind of a problem that is effecting the auditory response to sound, if you stress the system and you see that the system cant keep up it becomes clinically useful and provides a red flag if the pt. isnt keeping up.
what are some things to consider when picking a stimulus rate?
- stimulate as fast as possible; save time
- adaptation
- latency and time epoch of the response of interest
Is there an ANSI standard for stimulus intensity?
- No ANSI Standard:
1. often referenced to normal threshold for that stimulus expressed as dBnHL
- referenced to sound pressure level:
if the stimuli are short (clicks, tone pips), we measure the sound pressure level of the peak of the stimulus, and express the level as peSPL.
what are some stimulus transducers?
headphones
insert earphones
loud speakers
bone vibrators
-the type of earphone can affect the quality of the click and therefore the response
what are some characteristics that are associated with using insert earphones?
- practical, more comfortable for babies than large circumaural earphones.
- comfortable if reference electrode is earlobe
- no ear canal collapse
- less electromagnetic stimulus artifact because sound source is separated from ear.
- stimulus artifact does not extend into recording epoch
define condensation
headphone diaphragm is displaced outwardly. the TM is displaced medially
define rarefaction
the headphone diaphragm is displaced inwardly and the TM is displaced laterally
name the pathway of recording evoked potentials
- neurons
- sum (cancel or add)
- send out a field
- travels up through the tissue of the brain
- through the dura
- through the skull
- through the scalp
- to the electrodes
what are some electrode characteristics
- material which conducts electricity (gold, tin, platinum)
- impedance/resistance-opposition to current flow
- it is important to have
- —-low impedance (more current flow, better response)
- —-balanced impedance across electrodes (equal contribution from each electrode
- voltage = current x impedance
stimulation rate
the shorter the latency the faster the rate
variability
the shorter the latency the smaller the variability
electrode position
(degree to which small shifts in electrode location alter waveform morphology)
the shorter the latency the more far-field the response
susceptibility to state changes
the shorter the latency the susceptible to changes in subject state
rate of maturation:
the shorter the latency the more rapidly maturation proceeds
Amplitude
the shorter the latency the smaller the amplitude
amplitude of subcortical potentials
less than 10 mV
amplitude of cortical potentials
greater than 10 mV
amplitude of abr
.2 mV
amplitude of MLR
1 mV
amplitude of LLAEP
1-10 mV
spectrum
the shorter the latency the higher the frequency specturm
frequency spectrum of ABR
30-1500 Hz
number of averages of ABR
2000
number of averages of MLR
1000
number of averages of LLAEP
100
frequency spectrum of MLR
10 - 100 Hz
frequency spectrum of late potentials
.1-30 Hz
frequency spectrum of EEG
1-12 Hz
condensation
- headphone diaphragm displaced outwardly
- TM displaced medially
Rarefaction
- headphone diaphragm displaced inwardly
- RETRACTION
- TM displaced laterally
impedance/resistance - opposition to current flow
important to have:
- low impedance (more current flow, better response)
- balanced impedance across electrodes (equal contribution from each electrode)
Voltage =
current * impedance
common mode rejection ratio (CMRR)
reducing the noise by subtracting the “common mode” the current that is common to the two electrodes (expressed in dB)
- rejection ratio - used by equipment manufacturers and expressed in dB
- better to have bigger than smaller ratio
Strategies for avoiding electrical noise
matched electrode impedances differential amplification grounding shielding filtering separate power cords from input to averager stimulus rate - not at multiples of 60
Why do we do ABRs?
diagnose hearing loss
CNS lesions / disorders
language - based learning problems (e.g. dyslexia)
auditory processing disorders
developmental delay
attention deficit disorder
central function with peripheral hearing loss (hearing aids, cochlear implants)
at-risk infants, autism, Alzheimer’s disease
impact of aging, hearing loss
Three types of Gamma waves
at rest
induced
evoked
induced gamma waves
response to a stimulus NOT time locked
- not phase-locked, jittery latency
- varies from trial to trial
- cannot average across many responses as you average it out
- time-frequency analysis is needed: average the power across trials
evoked gamma waves
response to a stimulus is time locked
- depend on synchrony
- dynamic
- reflect response patterns across population of neurons
Dendrites - postsynaptic potentials (PSP)
Axons - action potentials (AP)
Evoked Responses - reflect both PSP and AP
exogenous EP components
sensitive to stimulus manipulations
endogenous EP components
sensitive to psychological state of subject
- if they’re asleep, paying attention etc.
What are the three cochlear responses and their latencies?
Cochlear Microphonic (CM) 0 Summating Potential (SP) 0 Otoacoustic Emissions 0
What are the three brainstem and their latencies?
Auditory Brainstem Response (ABR) 1-12
Frequency Following Response (FFR) 6+
Brainstem Response to Complex Sounds (cABR) 6+
What are the middle latency responses and their latencies (MLR)?
Na, Pa, TP41, Nb, Pb, (P1) 10-60
What are the event related potentials and their latencies?
N1, N1b (N100), N1c (N150) (all from auditory cortex), P2, N2, Sustained negativity 80-250 Elicited with oddball paradigm mismatch negativity (MMN) 150-275 Nc 400-700 Processing negativity Nd 60-700 P300, P3a, P3b 250 - 350 N400 - 400
Electrocochleaography (ecochg) - where does the electricity around the cochlea come from?
- potential difference across hair cells
- dendrite potentials in 8th nerve
- action potentials along 8th nerve
Amplitude of cortical vs subcortical potentials
The shorter the latency the smaller amplitude
- subcortical: < 10 mV
- cortical: > 10 mV
What is latency?
point in time relative to the stimulus onset
What is a trigger?
beginning of time window, signals averaged to enable alignment of all stimulus presentation sweeps
What is a pre-stimulus interval?
period between trigger and stimulus, enables assessment of non-stimulus-related brain activity
Which has shorter recovery times, brainstem (earlier) or cortical (later) responses?
earlier responses have shorter recovery times than later
What are Gamma waves and what are their frequency?
- 31-120
- hyper brain activity which is great for learning
What are beta waves and what are their frequencies?
- 13-30
- here we are busily engaging in activities and conversation
What are alpha waves and what are their frequencies?
8-12 Hz
very relaxed, deepening into meditation
What are theta waves and what are their frequencies?
4-7 Hz
drowsy and drifting down into sleep and dreams
what are delta waves and what are their frequencies?
.5-3 Hz
deeply asleep and not dreaming
Exogenous
sensitive to stimulus manipulations (EP)
Endogenous
sensitive to physiological state of the subject (EP)
Where does electricity around the cochlea come from?
- potential difference across hair cells
- dendrite potentials in 8th nerve
- action potentials along 8th nerve
What are electric currents in the cochlea measured with?
electrocochleaography (ECochG)
