BRAINSTEM EVOKED RESPONSE AUDIOMETRY (BERA)
Definition: Brainstem Evoked Response Audiometry (BERA) is an objective electrophysiological test measuring response in the brain waves that are stimulated by a clicking sound to check the central auditory pathways (hearing) of the brainstem. It is a non-invasive technique to find the integrity of central auditory pathways through the VIIIth nerve, pons and midbrain.
Indications:
- Nervous system abnormalities
- Children with hearing loss
- To assess neurological functions
- Malingering patients
- Suspected acoustic neuroma
- Central pontine myelinolysis
Bera test Procedure
- The test is done in an air-conditioned room.
- Patient is asked to wash the hair the night before the test.
- Infants and small children need to be administered sedatives like triclofos sodium in a dose of 50 mg per kg of body weight or promethazine hydrochloride in a dose of 0.5mg per kg of body weight so that the child is deeply sedated during the test.
- Electrodes are placed on the patient’s scalp, along the vertex and on each earlobe.
- Patient in lying down position, eyes closed and preferably asleep.
- Earphones are put on the ear. The patient hears a clicking sound between 10 and 40 clicks per second through the earphones.
- The electrodes pick up the brain’s response and record it on the graph.
- It measures hearing sensitivity in the range of 1000–4000 Hz.
- In a normal person, seven waves are produced in the first 10 ms.
- The first, third and fifth waves are most stable and are used in measurements.
- The waves are studied for absolute latency, inter-wave latency (usually between wave I and V) and the amplitude.
- Wave V is the most reliable and easily identifiable wave in the BERA tracing.
BERA waves Interpretation
- Wave I - Distal part of CN VIII
- Wave II - Proximal part of CN VIII near the brainstem
- Wave III - Cochlear nucleus
- Wave IV - Superior olivary complex
- Wave V - Lateral lemniscus
- Waves VI - Inferior colliculus
- Waves VII - Medial geniculate body
Absolute latency:
Wave |
Latency (ms) |
Wave I |
1.55 - 1.75 |
Wave III |
3.8 |
Wave IV |
5.5 - 5.85 |
Interaural latency:
Parameter measured |
Normal value (milliseconds) |
Criteria for abnormality (milliseconds) |
Interaural latency difference of wave V |
Less than 0.3 |
More than 0.3 |