EEG Evoked Potentials 5 ā Questions and Answers
Question 1: Which cognitive evoked potential component is considered the gold standard for assessing auditory discrimination and working memory?
- N100
- P200
- P300 (P3b) (Correct answer)
- N400
Correct answer: P300 (P3b)
The P300 (P3b) is an endogenous, task-related component elicited by target detection in an oddball paradigm, widely used to assess cognitive processing speed and memory.
Question 2: The N400 event-related potential is characteristically elicited by:
- Unexpected tones in an auditory oddball task
- Semantically incongruent words in a sentence (Correct answer)
- Visual pattern reversal
- Painful cutaneous stimulation
Correct answer: Semantically incongruent words in a sentence
The N400 is a negative deflection peaking ~400 ms that reflects semantic mismatch processing, elicited when a word violates the expected meaning of a sentence.
Question 3: Cortical somatosensory evoked potentials recorded over the scalp after median nerve stimulation include which early obligate component?
- N9
- N13
- N20 (Correct answer)
- P40
Correct answer: N20
N20 is the first cortical (primary somatosensory cortex) component of the median nerve SSEP, typically appearing ~20 ms post-stimulus in adults.
Question 4: Mismatch negativity (MMN) is unique among auditory evoked potentials because it:
- Requires the patient to actively attend to sounds
- Can be recorded during sleep or in unresponsive patients (Correct answer)
- Only occurs with painful stimulation
- Requires bilateral hearing for generation
Correct answer: Can be recorded during sleep or in unresponsive patients
MMN is a pre-attentive, automatic response to auditory change that can be recorded without voluntary attention, making it useful for assessing auditory discrimination in comatose patients.
Question 5: In VEP testing, what is the main reason each eye is tested separately with the other eye patched?
- To reduce electrical interference between eyes
- To isolate each optic nerve's conduction independently (Correct answer)
- To improve signal averaging efficiency
- To prevent binocular rivalry artifacts
Correct answer: To isolate each optic nerve's conduction independently
Monocular testing isolates the optic nerve pathway anterior to the chiasm, allowing detection of unilateral demyelination or compressive lesions of a single optic nerve.
Question 6: Which BAEP wave is generated by the auditory nerve (cranial nerve VIII) and is commonly absent in acoustic neuroma?
- Wave I only (Correct answer)
- Wave II
- Wave III
- Wave V
Correct answer: Wave I only
Wave I is generated by the distal auditory nerve; its absence alongside preserved waves generated more centrally suggests a peripheral CN VIII lesion such as acoustic neuroma.
Question 7: Tibial nerve SSEPs are primarily used to monitor which spinal cord tracts during surgery?
- Anterior corticospinal tracts
- Dorsal columnāmedial lemniscus pathway (Correct answer)
- Spinothalamic tracts
- Rubrospinal tracts
Correct answer: Dorsal columnāmedial lemniscus pathway
Tibial nerve SSEPs ascend via the posterior (dorsal) columns carrying proprioception and fine touch, so they specifically monitor the dorsal columnāmedial lemniscal pathway.
EEG Evoked Potentials 5
Which cognitive evoked potential component is considered the gold standard for assessing auditory discrimination and working memory?