Development of activity patterns in auditory nerve fibres of pigeons

Abstract

Little is known about inner ear development in pigeons. This paper addresses the question of maturation in activity patterns of pigeon auditory nerve fibres. 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 fibres in immature animals (about 40 spikes/s) are half that found in adults. Spontaneous discharge rate does 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 fibres are below 1.3 kHz. Sharpness of tuning is already adult-like in 1-week-old animals. Inter-spike time interval histograms (ISTH) of auditory fibres recorded in animals of all age groups often show Poisson-like distributions. Preferred intervals are found in 10% of the ISTHs of fibres in immature animals but in 30% of adults. Cross-correlations between heart beats of the animal and spontaneous activities show good correlation for about 70% of the fibres in immature animals. With the growth of the animals, the number of fibres 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 the inner ear is conceivable.