few slides on basics of auditory evoked responses. will be helpful for neurology and audiology students and healthcare professionals

1. BRAINSTEM AUDITORY
EVOKED RESPONSE
MEENAKSHY SUDEEP
BSc NEUROTECHNOLOGY

2. HISTORY
• 1967, Sohmer and Feinmesser were the first to
publish ABRs recorded with surface electrodes in
humans which showed that cochlear potentials
could be obtained non-invasively
• 1971, Jewett and Williston gave a clear description
of the human ABR and correctly interpreted the later
waves as arriving from the brainstem
• 1977, Selters and Brackman published landmark
findings on prolonged interpeak latencies in tumor
cases

3. • 1974, Hecox and Galambos showed that ABR
could be used for threshold estimation in adults
and infants
• 1975, Starr and Anchor were the first to report
effect on ABR of CNS pathology in the brain stem

4. BAEP
• Brainstem Auditory Evoked Potentials are electric
field potentials generated with repetitive
auditory stimulation of auditory pathways

5. BAEP
• Brainstem auditory evoked potentials (BAEPs)
reflect neuronal activity in the auditory nerve,
cochlear nucleus, superior olive, and inferior
colliculus of the brainstem
• These potentials are recorded from ear and
vertex in response to brief auditory stimulation
• BAEP comprise five or more waves within 10ms
stimulus

7. BAEP
• Short Latency Response < 10mS
• Middle Latency Response 10 – 100mS
• Long Latency Response >100ms

8. BAEP: ELECTRODE
PLACEMENT
• RECORDING ELECTRODE: Cz placed at vertex
• REFERENCE ELECTRODE: A1 placed at ipsilateral
ear lobule or mastoid process
• GROUND ELECTRODE: A2 p0laced at
contralateral ear lobule

9. METHOD OF RECORDING
• To elicit and record BAEPs an auditory stimulus is
delivered to the patient via headphones
• Auditory stimulus is a square wave pulse of 0.1
ms duration
• The pulse can move earphone diaphragm either
towards or away from the ear
• The earphone movement towards the ear is
called condensation phase stimulus
• The stimulus away from patients ear is called
rarefaction stimulus

10. • Intensity of stimulation in stimulating ear rangs
from 70 to 100 dB
• As one ear is stimulated with clicks, the other is
masked with white noise, typically 30 to 50 dB
• This method helps to prevent the undesired
coactivation of the contralateral ear caused by
bony conduction from the ipsilateral stimulated
ear
• Atleast 2000 trials are averaged to get a good
quality recording. 2 to 3 repetitions are done
and superimposed to check for reproducibility

11. BAEP waveform

13. INTERPRETATION OF RESULT
• When interpreting the ABR, we look at
AMPLITUDE (the number of neurons firing)
LATENCY (the speed of transmission)
INTERPEAK LATENCY (the time between peaks)
INTERAURAL LATENCY (the difference in wave V
latency between ears

14. • Wave I should be observed but will only be
present ipsilaterally
• Wave III and V should be detactable in all healthy
individuals
• Wave VI and VII appear variably after wave v

15. MEASUREMENT AND
NORMAL VALUES OF BAEP
• The following parameters are measured foe the
analysis of BAEP
 absolute latency and amplitude
Interpeak latencies
Amplitude ratio of wave v to I or waves IV-V
complex and I
Inter ear interpeak difference

16. NORMAL VALUES

17. ABNORMAL BAEP
• BAEP abormalities may include one or more of
the following
Absence of waveform
Abnormal absolute or interpeak latencies
Amplitude ratio abnormality
Right to left assymetry

18. CLINICAL
NEUROPHYSIOLOGICAL
CORRELATIONS
• BAEP has been studied in numerous neurological
disorders
• The most important clinical applications are
CEREBELLOPONTINE ANGLE TUMOR
INTRINSIC BRAIN TUMOR
MULTIPLE SCLEROSIS
COMA
STROKE

19. PATIENT RELATED
VARIABLES AFFECTING BAEP
• Age
• Gender
• Level of arousal
• Body postion
• Temperature
• Pre existing hearing loss

20. References
• Text book of clinical neurophysiology by UK
Mishra and J kalitha
• Google images

21. THANK YOU…..