The document discusses the history and methodology of brainstem auditory evoked responses (BAER), highlighting key milestones and studies from 1967 onwards. It details the process of eliciting and recording BAERs, including electrode placement and stimulation techniques, as well as the interpretation of results. Additionally, it addresses clinical applications and variables that may influence BAER outcomes.

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…..