1
Q
What are the fast-latency responses?
A
- the auditory brainstem response (ABR)
- the auditory steady-state response (ASSR)
- the frequency-following response (FFR)
2
Q
You can get fast-latency responses when people are ____.
A
sleeping
3
Q
What are the cochlear responses?
A
- OAEs
- EcochG
4
Q
What are the 4 parts of an OAE?
A
- spontaneous (SOAE)
- transient (TEOAE)
- distortion product (DPOAE)
- stimulus frequency (SFOAE)
5
Q
What are the three parts of an EcochG?
A
- compound action potential (CAP)
- summating potential (SP)
- cochlear microphonic (CM)
6
Q
Where are responses coming from with an EcochG?
A
Cochlea and AN
7
Q
What does EcochG stand for?
A
Electrocochleographic
8
Q
What are the cortical auditory evoked responses?
A
- auditory middle-latency response
- auditory slow and late-latency response
9
Q
What are the middle-latency responses?
A
- transient MLR
- 40 Hz ASSR
10
Q
What are the slow and late-latency responses?
A
- P1-N1-P2 complex
- Mismatch negativity (MMN)
- P300 response
- N400 response
11
Q
True or false: cortical auditory evoked responses are commonly used in audiology?
A
False: used more in psychology
12
Q
Are objective measures or behavioural measures superior for testing brain activity?
A
behavioural
13
Q
What are the two ways to measure brain activity?
A
- Hemodynamic / Metabolic
- Electrical (EEG) or magnetic (MEG)
14
Q
What are the tests used with measuring Hemodynamic / Metabolic activity?
A
- PET
- fMRI
- Optical
15
Q
Describe the Hemodynamic / Metabolic approach
A
- rich blood supply to brain
- thinking requires blood
16
Q
Hemodynamic / Metabolic: spatial and temporal resolution
A
- spatial resolution is very good
- temporal resolution is poor (slow because you are looking at something that happens after the fact)
17
Q
Explain oxygen rich vs. oxygen poor blood
A
oxygen-rich and oxygen-poor blood has different magnetic properties, BOLD or T2* imaging based on loss of magnetization related to use of oxygen released (by blood) to cells that are firing
18
Q
What are the tests used with measuring electrical or magnetic activity?
A
- electrical (EEG)
- magnetic (MEG)
19
Q
Describe the electrical or magnetic approach
A
- neurons have electrical properties that can be directly recorded (single unit)
- electrical activity of many neurons sums to create voltage changes at the scalp (e.g. ABR/MLR/ERP)
- electrical activity also creates magnetic fields that can be measured at the scalp (MEG)
20
Q
electrical or magnetic: spatial and temporal resolution
A
- spatial resolution is poor (because looking at what multiple neurons are doing, not a single one)
- temporal resolution is very good
21
Q
What are some differences between electrical and magnetic imagine?
A
- Magnetic imaging is very expensive
- Magnetic instead of electrical because nothing is distorted by the scalp
- Electrical imagine isn’t expensive and is used often in clinic
22
Q
Optical imaging of changes in ____ with tonal stimulation in the chinchilla
A
Blood flow
23
Q
What is the hemodynamic approach typically used for?
A
- Used for studying the structure and function of the cortical networks involved in speech perception and language
- Used for studying high level things (networks, how different parts of the brain are involved in different things)
24
Q
Why is the hemodynamic approach not used in audiology assessment?
A
- poor temporal resolution
- expensive
- invasive
- requires compliant subject (awake)
- although referrals may be indicated (e.g., MRI)
25
What is the electrical/magnetic approach typically used for?
used for estimating hearing thresholds, detecting space-occupying lesions, assessing neural integrity and timing at multiple levels (cochlea to cortex)
26
the ____ approach is used extensively in audiological clinical assessment.
elecetrical/magnetic
27
Name 4 reasons why electrical/magnetic approaches are common in audiology clinic assessments
1. excellent temporal resolution
2. inexpensive and clinically available
3. non-invasive
4. little compliance is needed
28
why is the electrical/magnetic approach used in audiological clinical assessment?
- excellent temporal resolution
- inexpensive (i.e., EEG), clinically available
- non-invasive
- little compliance required
29
What setting are electrical/magnetic approach most commonly used in?
hospital
30
Electricity is movement of charge from ____ potential to ____ (like water)
high, low
31
Rate of flow is current (I) measured in ____
amps
32
Resistance to flow (R) is ____
resistance
33
Potential difference (V) is measured in ____
Volts
34
sodium-potassium pump moves ____ outside cell and ____ inside cell
Na+, K+
35
How much energy in the brain does the sodium-potassium pump use?
70% is used to reserve this resting potential
36
The sodium pump in the brain allows cells to have ____ resting potential
negative
37
calcium pump keeps ____ outside of cell
Ca2+
38
membrane is more permeable to ____ (about 40x)
K+
39
how does the sodium-potassium pump work?
- some potassium flows out (because of concentration gradient)
- but then more positive charge outside of cell, so electrical force pulls against this, leads to charge of about –80 mV
- leakage of Na+ changes this to about –65 mV
40
Where is resting potential?
-65mV
41
Neurotransmitters (e.g., glutamate) increase ____ of membrane to Ca2+ or Na+
permeability
42
What happens when the cell has a positive potential?
This triggers a closure of sodium channels and an opening of potassium channels, membrane potential swings back to negative, overshooting resting potential (hyperpolarized)
43
What are the two sides to the electric neuron?
1. action potentials
2. post-synaptic potentials
44
Explain action-potentials
- the output side
- all or none (digital or binary)
- fast!
45
Explain post-synaptic potentials
- the input side (what’s happening at the dendrites)
- graded (analogue)
- slow
- it’s the sum activity of lots of other neural action potentials
46
Explain the action potential bb gun anaolgy
- consider action potential like firing a BB gun (all or none)
- Bob is getting shot with the BB gun repeatedly… a post-synaptic potential is Bob’s mental state (not all or none, changes more slowly)
- once Bob gets to a certain point, he fires his BB gun!
47
What causes excitation?
inflow of Na+ into the dendrite or cell body due to neurotransmitter such as glutamate
48
A ____ is low potential
sink
49
A ____ is high potential
source
50
What happens to the post-synaptic potential during excitation?
- the cell membrane more positive (source)
- the surrounding extracellular fluid negative (sink)
51
Explain the dipole electric field in volume conductor
- In the extracellular space, current flows from sources (+) to sinks (-)… i.e., towards places where neurons are being excited
- It will take all possible paths and go to all possible places
52
The extracellular sinks and sources create voltage patterns that can be recorded at the ____
scalp
53
What way does current flow INSIDE the cell?
sink --> source
54
What does isotropic mean?
equal in all directions
55
what does anisotropic mean?
different properties in different directions
56
Is the extracellular space isotropic or anisotropic? Heterogenous or homogenous?
- ansiotropic and hetergeneous
- but linear at large scales (can ignore the fine details)
57
____ and ____ distort electric fields
Skull, scalp
58
the dipole field of a single neuron is too ____ to be recorded at the scalp
small (a lot of neurons need to work together and fire at the same time in order to get a response)
59
Far-Field
- A couple cm away
- Measuring on the scalp you are a few cm away
- Can get larger responses when people are upside-down
60
Does EEG relate to a single neuron?
No, it relates to many neurons acting together
61
Explain spatial summation
In order to be detected without averaging, responses must occur in many neurons (at least 60 million) at roughly the same time
62
How many mm thick is the cortex?
3-5 mm thick
63
How many layers is the cortex?
6
64
What cells make up the cortex and how are they aligned?
large pyramid cells, aligned in the same direction (in an open field)
65
cortical pyramid cells form an ____ field
open
66
true or false: both pyramid, thalamic cells, and axons form open fields?
false: pyramid cells do, but thalamic cells & axons don't
67
describe the orientation of neurons in an open and closed field
in an open field, they are all aligned parallel to each other
in a closed field, they are all tangled together
68
Dipole fields must be aligned to sum at the ____
scalp
69
Dipole fields must be temporally ____ to sum at the scalp
coincident
70
What two things do you need to generate a far-field response?
- spatial summation (which requires synchrony)
- an open field
71
What happens when many neurons work together, at the same time, in the same direction?
it creates a large dipole (battery) like a giant neuron
72
Most large responses are from ____
post-synaptic potentials (coordinated patterns of excitation or inhibition)
73
Do action potentials give rise to open fields?
Not really
74
do post synaptic potentials need to be precisely aligned to add up? why or why not?
no, they are slow
75
do action potentials need to be precisely aligned to add up? why or why not?
yes, because they are very quick (about a msec)
76
ABR is composed of ____
action potentials
77
are most large responses from pre or post synaptic potentials?
post synaptic
78
With an EEG we are looking at ____ activity
spontaneus
79
Is stimulus needed for an EEG?
No
80
What is the EEG recording?
The scalp-recorded EEG is a pattern of voltage changes reflecting primarily post-synaptic activity (not action potentials)
81
What is the EEG picking up?
- only a small number of neurons are spiking at any given time
- post-synaptic potentials are slow and wide-spread
- the pyramid cells in the cortex produce open fields
82
With the EEG, oscillations likely reflect what?
Thalamocortical circuit dynamics
83
Explain the input/output of the brain
- The brain is a system that oscillates without input, not just input-output
- Only 5-10% of input is coming from the outside
- The brain is highly inwardly focused
84
All sensory input passes through the ____
Thalamus (except olfaction)
85
Sensory input targets pyramidal neurons in layer ____ of the thalamus
IV
86
What % of connections in layer IV are from other parts of the cortex?
90-95%
87
Are there more outgoing (corticothalamic) neurons or more incoming (thalamocortical) neurons?
10x as many outgoing
88
The brain is a complex system that is only perturbed by ____ input
external
89
What are the 5 rhythms of EEG?
1. Alpha
2. Beta
3. Gamma
4. Delta
5. Theta
90
Alpha occurs at which frequencies?
8-12 Hz (around 10 Hz)
91
Beta occurs at which frequencies?
13-20 Hz (around 20 Hz)
92
Gamma occurs at which frequencies?
>20 Hz (big peak around 40 Hz)
93
Delta occurs at which frequencies?
0.5-3 Hz (slow waves when deeply sleeping)
94
Theta occurs at which frequencies?
4-7 Hz (between delta and alpha)
95
What does gamma stimulate?
cortical columns
96
What does theta influence?
memory, communication, and syllabic rate
97
Eyes closed vs. eyes open EEG
Eyes closed
- A huge peak around 10Hz (alpha)
- When eyes are closed you aren’t processing visual information
- If asked to visualize something when eyes closed, alpha can decrease
Eyes open
- Flattens out (decreases as you go up in frequency)
- Lose alpha because they are processing what they are seeing
98
Where is alpha in the brain?
Alpha is everywhere in the brain (but prominent over visual cortex)
99
Where is beta in the brain?
beta is mostly motor and sensory cortex
100
What do the O, P, C, F, and Fp mean on an EEG?
O = occipital (can see that alpha is big until eyes are open)
P = parietal
C = central
F = frontal
Fp = frontal pole (forehead)
101
When eyes are closed, there is lots of ____, the brain is very ____
alpha, synchronized
102
When the eyes are open, ____ goes away, there is ____
alpha, desynchronization
103
What is the main clinical use of EEG?
tracking sleep
104
What are the stages of sleep?
stage 1: very similar to being awake
Stage 2: k complex and bursts of spindles
Stage 3: slow waves and spread out in time (delta waves)
Stage 4: more than 50% of what you are looking at is delta waves
105
One year after Berger’s discovery of EEG, the first auditory evoked response was recorded from the auditory nerve of a ____
Cat
106
auditory evoked responses refers to ....
electrical stuff occurring in response to sound
107
what did Pauline Davis note in EEGs when patients were stimulated with a loud sound?
k-complex
108
why do we think Pauline Davis named the k-complex the k-complex?
thought that someone knocked on the door then she discovered it
109
Who are the father and mother of auditory evoked responses?
Hallowell Davis and Pauline Davis
110
why was progress in auditory evoked response studies slow?
- becuase the spontaneous EEG was much larger than activity evoked by auditory stimuli
- harder to get and record
111
all early work with auditory evoked responses included what? like how did people study it?
looking at electrical responses from the cochlea using invasive electrodes (usually placed on the round window)
112
how close/far does an electrode have to be for it to be considered near vs far field?
- near field = electrode is in/on the structure
- far field = several cm away
113
What are the pros of near-field recording?
- can record post-synaptic potentials and spikes in individual neurons
- can record in closed fields (spatial alignment of dipole fields not necessary)… e.g. thalamus, nuclei
- can record very localized activity
- much larger than far-field
- e.g. CAP is 100 times larger at cochlear wall (e.g. promontory) than at earlobe or mastoid
114
What are the cons of near-field recording?
- invasive, often limited to animal studies
- small-scale neural activity might not relate to perception and cognition
115
What was the response averager?
- From the 1950s
- Made it possible to detect responses that were smaller than the background EEG activity
116
What is a more modern example of response averaging?
face averaging
117
what are the 2 assumptions of signal averaging?
1. auditory responses should be time locked to stimulus
2. background activity (EEG) should not be time locked
118
with signal averaging, what are we trying to preserve and reduce?
- trying to preserve time-locking
- trying to reduce background activity
119
since the auditory response should be the same after each stimulus, averaging the period after each stimulus should ____ this activity
preserve
120
since the background activity should not be the same after each stimulus, averaging should ____ this activity
reduce
121
Overall, what does averaging show you?
averaging shows you what stays the same on each trial
122
Where do late potentials come from?
the cortex
123
ABR refers to actions potentials that come from where?
The AN and brainstem
124
what are the 5 ways we can classify evoked responses?
1. latency
2. stimulus dependence
3. source tissue
4. source location
5. type of activity
125
which classification type is the easiest and most common?
latency
126
classify the following auditory evoked responses by short-, mid-, or long-latency:
ECochG
MLR
LLR
ABR
ECochG and ABR = short (<10ms)
MLR - mid (10-50ms)
LLR = long (50+ms)
127
ABR is sometimes called the ____ latency response
fast (short = fast)
128
Auditory Evoked Responses picture
129
Need better resolution and more amplification to pick up ____ vs. ____
fast latency response (ABR) vs. long latency response
130
What are 3 ways to describe potentials?
- exogenous
- endogenous
- mesogenous
131
what does exogenous mean and give an example
- determined by stimulus
- cochlear microphonic
- AEPs
132
what does endogenous mean and give an example
- your reaction to something
- N400 - response to a word that doesn't make sense in the semantic context
- ERPs
133
what does mesogenous mean and give an example
- partially determined by the stimulus, partially by perception/cognition
- P1-N1-P2 complex
134
is stimulus dependence an easy or hard way to classify?
hard
135
what determines a response for endogenous?
attention
136
what are the 2 things we observe in EEGs associated with auditory stimuli based on time locked changes?
- AEPs
- ERPs
137
What are auditory evoked potentials (AEPs)? Give examples
- responses that are determined by the stimulus (exogenous)
- ECochG, ABR, MLR, ASSR (80 Hz and 40 Hz), FFR
138
What are event-related potentials (ERPs)? Give examples
- responses that relate to events
- often relate to cognitive processes
- affected by attention (endogenous)
- LLR, MMN, P300, N400
139
source tissue includes ____ activity, which includes what 3 things?
Neural
- Action Potentials
- Post-Synaptic Potentials
- Myogenic or Artifact
140
What does source location refer to?
Where it occurs
- Planum Temporale,
- Heschl’s Gyrus
- Cochlear Nucleus
141
what are the 5 types of potentials?
- spontaneous
- transient
- sustained
- steady state
- induced
142
What are transient potentials?
play a stimulus and get a response (happens once after the stimulus)
143
What are spontaneous potentials?
no stimulus, measuring waves from the brain
144
What are induced potentials?
- changes in the spontaneous activity in response to a stimulus
- play a sound and see changes in the alpha (induced change)
145
What are steady-state potentials?
activity that follows the stimulus in some way
146
What are sustained potentials?
EcochG, a pedestal response (constant positivity or negativity), does not fluctuate with the stimulus
147
Onset and offset responses are ____
transient
148
What is used for a neuropathy assessment?
EcochG
149
What are ABR and ASSR used in?
- peripheral hearing assessment (in babies)
- neurological diagnosis
- suprathreshold tests (discrimination)
- speech-evoked responses
150
true or false: EEGs in clinical audiology can also be used to detect hidden hearing loss and for advanced assessments?
true
Electrophysiology
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