Development of activity patterns in auditory nerve fibres of pigeons

Little is known about inner ear development in pigeons. This paper addresses the question of maturation in activity patterns of pigeon auditory nerve fibers. Pigeons that were 1, 2 and 4 weeks and 1, 2, 3, and 4 years old were investigated. Adult-like activity patterns are found 4 weeks post- hatching. Spontaneous activities of fibers in immature animal (about 40 spikes/s) are half that found in adults. Spontaneous discharge rate dose not increase with decreasing characteristic frequency (CF) of the fibre if the animals are immature. Rate thresholds are less sensitive in immature animals. Differences between the age groups are generally significant if the CFs of the fibers are below 1.3 kHz. Sharpness of tuning is already adult-like in 1- week-old animals. Inter-spike time interval histograms (ISHT) of auditory fibers recorded in animals of all age groups often show Poison-like distributions. Preferred intervals are found in 10% of the ISTHs of fibers in immature animals but in 30% of adults. Cross-correlations between heart beats of the animals, the number of fibers showing correlation of spontaneous activities and heart beats decreases to about 40%. The basilar papilla of a 1-week-old animal is smaller than in an adult animal (by 10% in length and by 10% in width), judged by scanning electron microscopy (SEM). Changes of activity patterns in this study are likely to be a result of maturation of the middle ear. In addition to the latter, development of inner ear is conceivable.