Principle Behind BERA Testing
BERA (Brainstem Evoked Response Audiometry) measures neural electrical activity generated in the cochlea, auditory nerve, and brainstem in response to acoustic stimuli delivered via earphones, using surface electrodes to record these responses. 1
Core Physiologic Mechanism
BERA records neural activity from the peripheral auditory system, eighth cranial nerve, and brainstem auditory pathway. 1 The test uses surface electrodes placed on the scalp to detect electrical potentials generated as sound travels through the auditory system. 1, 2
Key Technical Components
- Acoustic stimuli (clicks or tone bursts) are delivered through earphones to stimulate the auditory system 1
- Surface electrodes record the resulting neural activity as it propagates through the auditory pathway 1, 2
- Repetitive identical stimuli are presented and the electroencephalographic responses are averaged to produce distinct positive and negative deflections (waves) 3
- Wave reproducibility, morphology, and consistent peak latencies are used for clinical interpretation rather than absolute amplitude values 4
What BERA Detects vs. What It Misses
BERA Can Detect:
- Sensory (cochlear) hearing loss affecting the peripheral auditory system 1
- Neural conduction disorders involving the eighth nerve or auditory brainstem pathway 1
- Auditory neuropathy/dyssynchrony when using both condensation and rarefaction stimuli to identify cochlear microphonic presence 1
- Retrocochlear pathology including vestibular schwannomas, though ABR alone misses 20% (range 8-42%) of intracanalicular tumors 1
Important Limitations:
- Outer and middle ear dysfunction can affect ABR results, causing abnormal waveforms even with normal neural function 1
- Mild or isolated frequency region losses may be missed by screening ABR 1, 5
- High-frequency sensorineural hearing loss may produce abnormal waveforms or absent waves 6
Clinical Applications in Neonatal Screening
Automated ABR technology is essential for universal newborn hearing screening because it incorporates automated response detection, eliminating individual test interpretation and screener bias. 1
Specific Screening Protocols:
- NICU infants require ABR screening rather than OAE alone due to higher risk for auditory neuropathy 5, 7
- Diagnostic ABR must include frequency-specific testing using air-conducted tone bursts to determine degree and configuration of hearing loss for amplification fitting 1, 7
- Both condensation and rarefaction stimuli are required for infants with risk factors like hyperbilirubinemia or anoxia to detect cochlear microphonic 1, 7
Advantages Over Other Testing Methods
ABR is superior to OAE testing because it assesses the entire auditory pathway from cochlea through brainstem, whereas OAE only reflects cochlear outer hair cell function. 1 This distinction is critical because neural conduction disorders and auditory neuropathy/dyssynchrony without concomitant sensory dysfunction will not be detected by OAE testing. 1, 5
Key Clinical Advantage:
- ABR is unaffected by anesthesia and drugs, making it ideal for sick or sedated infants 6
- The test is non-invasive and objective, particularly suitable for very young or critically ill infants 8
- Sedation may be required for diagnostic ABR as the infant must remain relatively quiet during testing 7, 6
Diagnostic Evaluation Timeline
Infants who fail initial screening must undergo comprehensive audiological evaluation including diagnostic ABR by 3 months of age. 7 The diagnostic battery should include frequency-specific ABR, click-evoked ABR with both polarities, OAEs, and tympanometry using 1000-Hz probe tone. 1, 7
Common Pitfall:
Standard test-retest variability for ABR fluctuates by ±5 dB, so changes less than 10 dB may not represent true threshold shifts. 4 Clinicians must focus on wave reproducibility across repeated trials rather than meeting specific amplitude thresholds. 4