EDT Evoked Potentials 1 — Questions and Answers
Question 1: Which nerve is typically stimulated at the wrist to obtain upper extremity somatosensory evoked potentials (SSEPs)?
- Median nerve (Correct answer)
- Ulnar nerve
- Radial nerve
- Musculocutaneous nerve
Correct answer: Median nerve
The median nerve at the wrist is the standard stimulation site for upper extremity SSEPs due to its reliable brachial plexus and cortical responses.
Question 2: What does 'P100' refer to in visual evoked potential (VEP) recordings?
- A positive polarity peak occurring approximately 100 ms after the visual stimulus (Correct answer)
- A negative peak occurring 100 ms before stimulus onset
- The 100th averaged response waveform
- A positive peak with amplitude of 100 µV
Correct answer: A positive polarity peak occurring approximately 100 ms after the visual stimulus
P100 is a positive-polarity component peaking around 100 ms post-stimulus and is the primary waveform evaluated in clinical VEP studies.
Question 3: What type of stimulus is used to elicit pattern-reversal visual evoked potentials?
- A checkerboard pattern that alternates black and white squares at a set rate (Correct answer)
- A single brief flash of white light
- An auditory tone burst at a fixed frequency
- Electrical stimulation of the retina
Correct answer: A checkerboard pattern that alternates black and white squares at a set rate
Pattern-reversal VEPs use a contrast-reversing checkerboard that produces more reproducible and reliable responses than flash stimuli.
Question 4: The N20 component recorded over the contralateral scalp in median nerve SSEPs is generated by which structure?
- Primary somatosensory cortex (Correct answer)
- Thalamus
- Cervical spinal cord
- Brachial plexus
Correct answer: Primary somatosensory cortex
N20 is the earliest cortical response to median nerve stimulation and is generated in the contralateral primary somatosensory cortex (area 3b).
Question 5: What is the primary purpose of signal averaging in evoked potential recordings?
- To improve signal-to-noise ratio by canceling random background EEG activity (Correct answer)
- To increase the intensity of the electrical stimulus
- To filter out frequencies above 100 Hz
- To synchronize stimulation with the cardiac cycle
Correct answer: To improve signal-to-noise ratio by canceling random background EEG activity
Averaging enhances the time-locked evoked response while random background noise cancels out mathematically, improving SNR proportional to the square root of the number of averages.
Question 6: Which evoked potential modality is the most widely used for intraoperative monitoring during spinal cord and spinal column surgery?
- Somatosensory evoked potentials (SSEPs) (Correct answer)
- Visual evoked potentials (VEPs)
- Brainstem auditory evoked potentials (BAEPs)
- Cognitive event-related potentials (P300)
Correct answer: Somatosensory evoked potentials (SSEPs)
SSEPs monitor the integrity of the dorsal column-medial lemniscal pathway and are the established standard for intraoperative neurophysiological monitoring during spinal surgery.
Question 7: What does the Erb's point potential represent in upper extremity SSEP recordings?
- Brachial plexus activation recorded in the supraclavicular fossa (Correct answer)
- Cervical spinal cord synaptic response
- Thalamic relay response
- Initial cortical arrival of the sensory volley
Correct answer: Brachial plexus activation recorded in the supraclavicular fossa
The Erb's point electrode is placed in the supraclavicular fossa and records the near-field potential generated by activation of the brachial plexus, confirming peripheral pathway integrity.
EDT Evoked Potentials 1
Which nerve is typically stimulated at the wrist to obtain upper extremity somatosensory evoked potentials (SSEPs)?