Phase locking in monaural and binaural medullary neurons: Implications for binaural phenomena

Abstract

The synchrony of neural impulses in response to low-frequency sinusoids was described for auditory medullary neurons [Dipodomys spectabilis]. In general, neural synchrony improved with increases in intensity and frequency of stimulation for monaural and binaural neurons when measurements were made in absolute time. An analysis of this population of neurons implied that 2 separate mechanisms were responsible for the decrease in synchrony found in many neurons as compared to primary-like neurons with high-locking ability. The 2 mechanisms were convergence of mistimed impulses and electrontonic changes which occurred in dendrites. An analysis of binaural vector strength data prpvided an explanation for physiological differences between cyclic and noncyclic vector strengths as a function of interaural time and reveals the effects of mistimed convergence upon neural synchrony. In contrast to the inferior colliculus, where the neurons discharge best with contralateral leads in time, superior olivary neurons exhibited no such preference. Some discharged best to ipsilateral while others to contralateral leads. This comparison revealed a striking difference in the coding characteristics of medullary and inferior colliculus neurons. The results were compared with the psychophysically determined difference limens.