This document discusses evoked potentials, which are electrical activities in the neural pathway generated in response to external stimuli. It focuses on three types of sensory evoked potentials: visual evoked potentials (VEP), somatosensory evoked potentials, and brainstem auditory evoked potentials (BEAP). VEP assess the visual pathway and look for abnormalities in P100 latency and amplitude. BEAP assess the auditory pathway by analyzing wave latencies and amplitudes, with abnormalities indicating lesions in the auditory nerve, brainstem, or cranial nerves. Evoked potentials are used to detect disturbances in the central nervous system.

1. EVOKED POTENTIALS
KEERTHI PRIYA MPT NEURO,
ASSISTANT PROFESSOR

2. INTRODUCTION
Electrical activities occurs in neural pathway due to external stimulus by light,
sound, electrical current, smell or taste.
Polyphasic with amplitude of 0.1-20mA
To detect disturbances in CNS

3. CLASSIFICATION
SENSORY POTENTIALS
MOTOR POTENTIALS
EVENT RELATED POTENTIALS

4. SENSORY
SOMATO SENSORY
EVOKED
POTENTIALS
VISUAL EVOKED
POTENTIALS
BRAINSTEM
AUDITORY EVOKED
POTENTIALS

5. VEP
Non invasive studies that measure the evoked response to visual stimuli.
Assess visual conduction pathway I,e optic nerve & anterior chiasma.
Types : Based on stimuli
1. Pattern reversal
2. Pattern on /off set
3. Flash

6. VEP
Procedure
Electrodes
Filters : Low cut=1-3 HZ
High cut =100-300 HZ

7. VEP
2 channels
Channel 1: oz FPz
Channel 2: oz linked
4 channels
Channel 1: Oz FPz
Channel 2: Pz FPz
Channel 3: L5 FPz
Channel 4: R5 FPz

8. VEP
NORMAL: N70,P100 & N135
P100
LATENCY 96.9 +/-3.6
AMPLITUDE 7.8 +/-1.9
DURATION 55.9 +/- 7.7

9. VEP
FACTORS AFFECTING VEP:
• Age
• Gender
• Eye dominance
• Eye movements
• Visual acuity
• Drugs

10. VEP ABNORMALITIES
P100 LATENCY IS PROLONGED:
 Multiple Sclerosis
Optic Neuritis
Usher’s Syndrome
Spinocerebellar Degeneration
Glaucoma

11. VEP ABNORMALITIES
Decreased amplitude in compressive optic nerve lesions
Normal in cortical blindness
Infections no abnormalities
Alcoholics abnormalities are reversed
Nutritional neuropathy latency is prolonged
Latency is prolonged in hereditary & degenerative diseases

12. BEAP
Evoked potentials caused by an aural stimulus positioned on scalp record response
to sound.
Aural stimulus activates central & peripheral auditory pathway.
Assess central & periphery auditory conduction pathway to rule out lesions in
auditory pathway & brainstem.

13. BEAP
Procedure
Electrodes
Filters : Low cut=100 HZ
High cut =3000 HZ

14. BEAP
2 channels
Channel 1: Ai Cz
Channel 2: Ac Cz
Ground : Fz

15. BEAP
NORMAL: Wave I -V

16. BEAP
WAVE I:
 Generator: Auditory Nerve
 Latency = 1.4 ms
 Absent in auditory nerve
WAVE II:
 Generator: Cochlear nucleus
Latency is prolonged
 wave II & III : M

17. BEAP
WAVE III:
 Generator: Superior Olivary Nucleus
 Latency decreases
 Bifid
 Prominent crest & troughs
WAVE IV & V:
 Generator: Wave IV: Lateral Leminiscus
Wave V: Inferior Colliculi
 Latency is 5.5. ms

18. BEAP
NORMAL:
Latency & Amplitude
Inter peak latency
Amplitude ratio of wave V/I or IV-V/I
Inter Ear Inter Peak Differences

19. BEAP
INTER PEAK LATENCY
I-V 8th cranial nerve to mid
brain or pons
4.5ms
I-III 8th cranial nerve to
lower pons
2.5ms
III-V Lower pons to mid brain 2.4ms

20. BEAP ABNORMALITIES
 Abnormal latency
Abnormal IPL
Abnormal amplitude ratio
Right to left asymmetry

21. BEAP ABNORMALITIES
CP ANGLE TUMOUR:
 Prolonged latency of III-V
 Prolonged I-III & I-V IPL
BRAIN TUMOUR:
Prolonged I-III & III-V IPL
MULTIPLE SCLEROSIS:
 Absence of wave V/ wave III
 Prolonged III-V IPL
Decrease amplitude of V/I

22. BEAP ABNORMALITIES
CP ANGLE TUMOUR:
 Prolonged latency of III-V
 Prolonged I-III & I-V IPL
BRAIN TUMOUR:
Prolonged I-III & III-V IPL
MULTIPLE SCLEROSIS:
 Absence of wave V/ wave III
 Prolonged III-V IPL
Decrease amplitude of V/I
COMA: Absence of wave III & V

23. THANK YOU