Postsynaptic inhibition can explain the concentration of short inter-spike-intervals in avian auditory nerve fibres.

Spontaneous and sound-evoked single-unit activity was recorded from afferent neurones in the cochlear ganglion of the anaesthetized pigeon. The histogram of successive intervals of spontaneous activity of 51% of neurones exhibited more short intervals than expected from a Poisson point-process description of spike times; for another 43% of neurones the point-process was Poisson. A model of spike generation was developed to account for the concentration of short spike-intervals. The proposed model contains inhibitory postsynaptic potentials at the afferent dendrite, in addition to the excitatory postsynaptic potentials. Not only does the model reproduce the first-order interval statistics of neural activity, but it provides a mechanism for improving phase-locking to the fundamental frequency of a sinusoid, and also offers an explanation for the presence of reciprocal synapses in the human cochlea.