Brainstem Auditory Evoked Responses (BAER)

Introduction

BAERs are a series of positive and negative waveforms that arise from neural structures associated with the ascending auditory pathway, including the cochlea, brainstem, and auditory cortex. Short latency BAERs (< 10 ms) are used to monitor brainstem function, whereas long‐latency BAERs (> 10 ms) are used to monitor cortical function.

Auditory pathways

When sound enters the ear, the sensory information is first transduced by the receptors in the cochlea (inner ear). The cochlea is composed of fluid-filled compartments separated by membranes. The membranes express hair cells that are 'tuned' to a particular frequency. Sufficient movement of the hair cells will depolarize individual fibers of the auditory portion of the VIII cranial nerve. There are inner and outer hair cells; the inner hair cells are involved in signal transduction and can connect to multiple axons of the auditory nerve. There are different types of electric potentials that are generated in the cochlea, including cochlear microphonics and summating potentials.

Stimulation

In the clinical setting, action potentials generated by the auditory nerve are elicited by click sounds or a tone burst.

Waveform

1. Peaks and neural generators
2. Latencies and interpeak latencies
3. Normal values