DEVELOPMENT OF ACTIVITY PATTERNS IN AUDITORY-NERVE FIBERS OF PIGEONS

Little is known about inner ear development in pigeons. This paper add resses the question of maturation in activity patterns of pigeon audit ory 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 ani mals (about 40 spikes/s) are half that found in adults. Spontaneous di scharge rate does not increase with decreasing characteristic frequenc y (CF) of the fibre if the animals are immature. Rate thresholds are l ess 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. Prefe rred intervals are found in 10% of the ISTHs of fibres in immature ani mals but in 30% of adults. Cross-correlations between heart beats of t he animal and spontaneous activities show good correlation for about 7 0% 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 I-week-o ld animal is smaller than in an adult animal (by 10% in length and by 10% in width), judged by scanning electron microscopy (SEM). Changes o f activity patterns in this study are likely to be a result of maturat ion of the middle ear. In addition to the latter, development of the i nner ear is conceivable.