Cortical Auditory Evoked Potentials Flashcards
What recording system is used for CAEPs?
- 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
Describe maturation effects on the CAEP.
- 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)
What are the prominent peak components of the CAEP?
- P1: sensation of sound
- N1: attention to sound
- P2: auditory object identification of sound
What does duration of response coincide with?
-Duration of stimulus
Why is there more variability in the CAEP?
- Typical waveform has a wide range of normal latencies and amplitudes
- Reduced temporal precision compared to at the level of the brainstem
What are sleep effects on the CAEP?
- Reduced peak amplitudes and poorer morphology
- Can see oscillatory response when patient is asleep
Describe the vulnerability of the P1-N1-P2 complex.
- 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)
How do CAEPs relate to SIN ability in children?
- 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
How do CAEPs in noise relate to language ability in children?
- 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
What are oddball paradigms?
-Presenting standard stimulus MOST of the time but occasionally presenting odd/non-standard stimulus
What are three oddball paradigms?
- P300
- MMN
- N400
What is P300?
- Diffuse (multiple neural generators)
- Multimodal (auditory, visual, somatosensory)
- Requires oddball paradigm
- Stimulus differences are large
- Most often obtained in an active-attention mode
What is P300 an index of?
- Gross discrimination
- Sequential information processing
- Short term memory
What are clinical applications of P300?
- Biomarker for alcoholism
- Alzheimer’s
- ADHD
- ASD
- APD
- LD
- Schizophrenia
How is P300 affected by age?
-Prolonged latency
Describe P300 and APD.
- 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
What is Mismatch Negativity (MMN)?
- 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
Where does MMN originate?
-Auditory thalamus and cortex, frontal cortex, non-primary pathway
Is MMN a direct or indirect measure?
- Indirect (derived)
- Difference wave between the standard stimulus waveform and the deviant stimulus waveform
Describe MMN in children with SLI.
- Groups: expressive SLI, receptive SLI, control
- Group differences were noted for speech stimuli but not for tones
Describe N400.
- Can be elicited with visual English words, auditory English words, or ASL signs
- Reduced N400 in TBI patients
What is the Acoustic Change Complex (ACC)?
- 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)
What are clinical applications of ACC?
- Benefits of training (CIs)
- Only investigational at this point
What EEG measures are attention-independent/pre-conscious?
- Brainstem response: ABR/FFR
- Cortical response: Na/P2/N2, MMN
What is a cortical response?
-Stimulus-locked post-synaptic potential
Why don’t the late latency responses work for clinical purposes?
-VARIABILITY
