INTERAURAL DELAY-DEPENDENT CHANGES IN THE BINAURAL DIFFERENCE POTENTIAL IN CAT AUDITORY BRAIN-STEM RESPONSE - IMPLICATIONS ABOUT THE ORIGINOF THE BINAURAL INTERACTION COMPONENT

Auditory brainstem responses (ABRs) evoked by dichotic clicks with 12 different interaural delays (ITDs) between 0 and 1500 mu s were record ed from the vertices of 10 cats under ketamine anesthesia. The so-call ed binaural difference potential (BDP), considered to be an indicator of binaural interaction (BI), was computed by subtracting the sum of t he two monaural responses From the binaural one. The earliest and most prominent component of BDP was a negative deflection (DN1) at a laten cy between 4 and 4.8 ms. Like all the other components of BDP, DN1 was also due to binaural reduction rather than enhancement of the corresp onding ABR wave, P4 in this case. Furthermore, the way its latency inc reased as a function of ITD was also not compatible with what would be predicted by the delay-line coincidence detector models based on the excitatory-excitatory units in the medial superior olive (MSG). We the refore proposed an alternative hypothesis for the origin of this BI co mponent based on the inhibitory-excitatory (IE) units in the lateral s uperior olive (LSO). The computational model designed closely simulate d the ITD-dependent attenuation and latency shifts observed in DN1. It was therefore concluded that the origin of this BI component in the c at's vertex-ABR could be the lateral lemniscal output of the LSO, alth ough the delay lines which have been shown to exist also in the mammal ian brain may play an important role in encoding ITDs.