Evoked Potentials

Question 1

What is averaging?

Answer 1

• apply a stimulus
• the response is time locked to the stimulus
• noise and other neuronal activity is random
• averaging will allow you to see only activity generated in response to signal

Question 2

What nerve is stimulated in a SSEP study

Answer 2

tibial for lower limbs
median for upper limbs

Question 3

Where do you record in SSEP

Answer 3

arm/leg, back neck and cortex

Question 4

What is the spinal columns for the median nerves

Answer 4

C3 and C4

Question 5

What is the spinal columns for the tibial nerve

Answer 5

L4-S3

Question 6

What reference is used in SSEP

Answer 6

frontal (Fz) or extracortical

Question 7

How many averages and runs are used in SSEPs

Answer 7

500/1,000
2 runs

Question 8

What is the latency in the cortex from the median nerve

Answer 8

N19

Question 9

What is the latency in the cortex from the tibian nerve

Answer 9

P37

Question 10

Name the relevant peaks from the tibial nerve

Answer 10

P37 and N45

Question 11

Name the relevant peaks from the median nerve

Answer 11

N9, N13 and P14
N19 cortex

Question 12

What are the applications for SSEPs

Answer 12

• correlation with imaging of brain or spine
• surgical monitoring
• prognostication after cardiac arrest or other brain injury

Question 13

What visual stimulus is used in a visual evoked potential study

Answer 13

flash or reversing checkerboard

Question 14

Where do you record for VEP

Answer 14

• O1 and O2 to a frontal reference (12cm from inion)

Question 15

Why do you cover each eye in VEP

Answer 15

to look at the function of each occipital nerve

Question 16

List other important factors for VEPs

Answer 16

1. patient attention
2. visual acuity
3. ambient light
4. intensity of stimulus
5. distance from screen

Question 17

what latency response should you see

Answer 17

large positive response (P100)

Question 18

Why are half fields used in VEPs

Answer 18

to see if lesion post chiasm

Question 19

What are the three latencies outlined in VEP

Answer 19

N75, P100, N145

Question 21

What are the applications for VEPs

Answer 21

• optic nerve disease
• can confirm functional demyelination in multiple sclerosis
• can help with investigation of visual loss

Question 22

If you use enough stimuli in BAEP what responses can you measure

Answer 22

medullary and pons

Question 23

How do you perform the auditory stimulus in BAEP

Answer 23

use earphones to play a click

Question 24

What electrodes are used

Answer 24

Cz to A1 and A2

Question 25

How many stimuli do you need in BAEP

Answer 25

up to 1,000

Question 26

How long does it take to get response from brainstem in BAEP

Answer 26

first 10ms

Question 27

What measurements are done in BAEP

Answer 27

latencies between I-V
amplitude and intra-peak latencies

Question 28

What are the applications for BAEP

Answer 28

• correlation with imaging for brain stem lesions
• evaluation of hearing loss
• surgical monitoring