Table 6.

BAEP waves and blink test

BAEP waves	Anatomic localization
I	Distal portion of the auditory nerve
II	Proximal portion of the auditory nerve or cochlear nuclear complex, in the upper part of the medulla, ipsilateral to the stimulation side
III	Cochlear nucleus or superior olivary complex in caudal pontine tegmentum, ipsilateral to the stimulation side
IV	Superior olivary complex (lateral lemniscus), contralateral to the stimulation side
V	Inferior colliculus located in the midbrain, contralateral to the stimulation side
Blink test	Response
After stimulation of the supraorbital nerve, three responses are recorded on eyelid orbicular muscles: an early ipsilateral (R1) response and the two (ipsi- and contralateral) late responses (R2)	R1 response generated at the level of the pons, R2 responses at the level of the trigeminal-spinal tract at the pons level, the medulla oblongata, and the caudal trigeminal-spinal nucleus

Brainstem lesions can result in absent or delayed peaks III and V, prolonged III–V and I–V inter-peak latency, or a reduced I/V amplitude ratio (< 0.5)

Delay or absence of R1 indicates a facial /trigeminal nerve injury. R2 can be delayed in comatose patient and is also bilaterally delayed or absent in Wallenberg’s syndrome (with a R1 preserved)