Cortical Auditory Evoked Potentials

Question 1

What recording system is used for CAEPs?

Answer 1

• International 10-20 system
• The “10” and “20” between electrodes refer to the fact that distances between adjacent electrodes are either 10% or 20% of the total front-back or right-left distance of the skull

Question 2

Describe maturation effects on the CAEP.

Answer 2

• Waveforms change dramatically with age
• Bigger is not always better (smaller response may just require less cortical energy)
• With age, peaks decrease in amplitude (P1 and P2, butN1 emerges)

Question 3

What are the prominent peak components of the CAEP?

Answer 3

• P1: sensation of sound
• N1: attention to sound
• P2: auditory object identification of sound

Question 4

What does duration of response coincide with?

Answer 4

-Duration of stimulus

Question 5

Why is there more variability in the CAEP?

Answer 5

• Typical waveform has a wide range of normal latencies and amplitudes
• Reduced temporal precision compared to at the level of the brainstem

Question 6

What are sleep effects on the CAEP?

Answer 6

• Reduced peak amplitudes and poorer morphology

- Can see oscillatory response when patient is asleep

Question 7

Describe the vulnerability of the P1-N1-P2 complex.

Answer 7

• Lots of rapid information in speech
• Speech sounds are complex
• The world is noisy
• Therefore, degraded neural processing of speech sounds in kids (associated with impaired perception of speech sounds, impaired development of language skills)

Question 8

How do CAEPs relate to SIN ability in children?

Answer 8

• Bottom SIN children need to allocate more cortical energy to understanding speech in noise than top SIN children
• Bottom SIN group has diffuse, over-allocation of neural responses
• AND these group differences are noted only in noise, not in quiet

Question 9

How do CAEPs in noise relate to language ability in children?

Answer 9

• CAEPs in noise are poorer for language-impaired but not normal-language children
• Difference between Q and N observed for language-impaired but not normal-language children

Question 10

What are oddball paradigms?

Answer 10

-Presenting standard stimulus MOST of the time but occasionally presenting odd/non-standard stimulus

Question 11

What are three oddball paradigms?

Answer 11

• P300
• MMN
• N400

Question 12

What is P300?

Answer 12

• Diffuse (multiple neural generators)
• Multimodal (auditory, visual, somatosensory)
• Requires oddball paradigm
• Stimulus differences are large
• Most often obtained in an active-attention mode

Question 13

What is P300 an index of?

Answer 13

• Gross discrimination
• Sequential information processing
• Short term memory

Question 14

What are clinical applications of P300?

Answer 14

• Biomarker for alcoholism
• Alzheimer’s
• ADHD
• ASD
• APD
• LD
• Schizophrenia

Question 15

How is P300 affected by age?

Answer 15

-Prolonged latency

Question 16

Describe P300 and APD.

Answer 16

• Children ages 7-14 with reading and writing disorders
• APD tests: SSW and SIN tasks
• P300: listened to 750 and 2000 Hz tones
• Instructed to listen for rare tone which occurred in 1:4 interval
• Children divided into 2 groups based on P300 latency (early and later latency groups)
• Children in the later latency group had abnormal SSW and SIN results
• Results were difficult to classify in single individual

Question 17

What is Mismatch Negativity (MMN)?

Answer 17

• Response to stimulus change (echoic memory)
• Objective measure of auditory discrimination
• Elicited by minimal (just perceptible) acoustic differences in: frequency, intensity, duration, location, phonetic content, interstimulus interval, sound patterns, speech, music, etc.
• Passively elicited, does not require a behavioral task
• Can be tested in newborn infants
• Analyzed for latency/amplitude or area under the curve

Question 18

Where does MMN originate?

Answer 18

-Auditory thalamus and cortex, frontal cortex, non-primary pathway

Question 19

Is MMN a direct or indirect measure?

Answer 19

• Indirect (derived)

- Difference wave between the standard stimulus waveform and the deviant stimulus waveform

Question 20

Describe MMN in children with SLI.

Answer 20

• Groups: expressive SLI, receptive SLI, control

- Group differences were noted for speech stimuli but not for tones

Question 21

Describe N400.

Answer 21

• Can be elicited with visual English words, auditory English words, or ASL signs
• Reduced N400 in TBI patients

Question 22

What is the Acoustic Change Complex (ACC)?

Answer 22

• Aka P1-N1-P2 change complex
• CAEP analogous to N1/P2
• A response to change in an ongoing acoustic stimulus (NOT an oddball paradigm)
• EX: change in intensity, frequency (formant)

Question 23

What are clinical applications of ACC?

Answer 23

• Benefits of training (CIs)

- Only investigational at this point

Question 24

What EEG measures are attention-independent/pre-conscious?

Answer 24

• Brainstem response: ABR/FFR

- Cortical response: Na/P2/N2, MMN

Question 25

What is a cortical response?

Answer 25

-Stimulus-locked post-synaptic potential

Question 26

Why don’t the late latency responses work for clinical purposes?

Answer 26

-VARIABILITY