AUDITORY BRAIN-STEM RESPONSE FINDINGS IN BRAIN-STEM ISCHEMIA FOLLOWING SELECTIVE OCCLUSION OF THE ANTERIOR INFERIOR CEREBELLAR ARTERY IN THE RAT

Auditory brainstem responses (ABRs) were measured ipsilaterally (n = 13) or contralaterally (n = 5) after inducing permanent right or left anterior inferior cerebellar artery (AICA) occlusion. Three types of wave pat terns were classified when ABRs were recorded ipsilaterally. In type 1 (n = 4) all components disappeared; in type 2 (n = 2) all components disappeared transiently and then reappeared; and in type 3 (n = 7) only the latency difference between components I and IV increased. These findings indicate that all components reappeared in type 2 responses because cochlear blood flow was re-established quickly by collateral circulation, while type 3 changes reflected the relative sensitivity of the cochlea to ischemic damage when compared with the rest of the auditory pathways. When the ABRs were recorded contralaterally, characteristic findings included a delay in latency of component IV and a significant increase in inter-peak latency in components I-IV and IIb-IV.