An investigation of dendritic delay in octopus cells of the mammalian cochlear nucleus

Octopus cells, located in the mammalian auditory brainstem, receive their excitatory synaptic input ex-clusively from auditory nerve fi□bers. They respond with accurately timed spikes but are broadly tunedfor sound frequency. Since the representation of information in the auditory nerve is well understood, itis possible to pose a number of questions about the relationship between the intrinsic electrophysiology,dendritic morphology, synaptic connectivity, and the ultimate functional role of octopus cells in thebrainstem. This study employed a multi-compartmental Hodgkin-Huxley model to determine whetherdendritic delay in octopus cells improves synaptic input coincidence detection in octopus cells by com-pensating for the cochlear traveling wave delay. The propagation time of post-synaptic potentials fromsynapse to soma was investigated. We found that the total dendritic delay was approximately 0.275ms. It was observed that low-threshold potassium channels in the dendrites reduce the amplitude de-pendence of the dendritic delay of post-synaptic potentials. As our hypothesis predicted, the model wasmost sensitive to acoustic onset events, such as the glottal pulses in speech when the synaptic inputswere arranged such that the model's dendritic delay compensated for the cochlear traveling wave delayacross the auditory nerve □fibers. The range of sound frequency input from auditory nerve □fibers was alsoinvestigated. The results suggested that input to octopus cells is dominated by high frequency auditorynerve □fibers.