What is the 10-20 system?
- Method that describes and applies the location of scalp electrodes
- Developed to ensure standardized reproducibility so results can be compared across time
- Based on the relationship between the location of an electrode and underlying area of cerebral cortex
What is the typical maturation in the CAEP response?
Children
- Most prominent components are P1 and N2
As you get older, the peaks are smaller and P1 becomes minimized
- N1 becomes more prominent
- N2 is minimal
Older people tend to have more exaggerated amplitudes for P1 and N1
How do you analyze the CAEP response?
Usually look at onset, but can also look at offset
- Duration of the stimulus coincides with duration of the response
Typical waveform
- Wide range of normal latencies and amplitudes
- A difference of 30 ms is not significant
What are the clinical applications of P1-N1-P2?
Inter-response correlations describe changes in morphology (timing)
Correlations in noise are poorer for LP than for NL children
- 2 groups have the same response in quiet, but in noise it breaks down
Resistance to degradation in noise relates to auditory processing
- The higher the inter-response correlation relates to higher auditory processing scores
Resistance to noise in cortical responses may underlie normal perception of speech
What CAEPs are elicited with an oddball paradigm?
P300, P3a, P3b
Mismatch negativity (MMN)
Processing negativity (Nd)
N400
What is the P300, P3a, P3b CAEP?
- Diffuse (multiple neural generators)
- Multimodal (auditory, visual, somatosensory)
- Stimulus differences are large, obvious
Index of:
- Gross discrimination
- Sequential information processing
- Short term memory
What are the clinical applications of P300, P3a, P3b?
- Biomarker for alcoholism
- Alzheimer’s
- ADHD
- Autism
- APD
- Language disorder
- Schizophrenia (auditory hallucinations)
What P300 results are seen in subjects with APD?
- Children ages 7 to 14 with reading and writing disorders
- APD tests: SSW and speech-in-noise performance tests
- Children within the later latency group had abnormal SSW and speech-in-noise test results
What is the mismatch negativity (MMN)?
- Response to stimulus change, echoic memory
- Objective measure of auditory discrimination
- Elicited by minimal (just perceptible) acoustic differences
- Passively elicited, does not require a behavioral task
- Can be tested in newborn infants
- Originates in auditory thalamus and cortex, frontal cortex, non-primary pathway especially
What are the acoustic differences which elicit a mismatch response in the MMN?
- Frequency
- Intensity
- Duration
- Location
- Phonetic content
- Inter-stimulus interval
- Sound patterns
- Speech
- Music
What is the acoustic change complex (AAC) (P1-N1-P2 change complex)?
- Cortical auditory-evoked response
- Analogous to N1/P2
- A response to change in an ongoing acoustical stimulus
- Not elicited by an oddball paradigm
What are the clinical applications of the P1-N1-P2 change complex?
Benefits of training- CIs
- Only investigational at this state
Why don’t the late responses work for clinical purposes?
- Variability in responses
- Don’t need to wear a cap for a cortical response
- Cannot say that one individual response is abnormal
