During development, the innervation of the cochlea - the inner ear region that is responsible for hearing - is controlled by neurotrophins and their high-affinity Trk receptors. To date, only the earliest postnatal effects of absent neurotrophin signalling on cochlear innervation have been described. Schimmang et al. now report the effects that disrupted neurotrophin signalling has on cochlear innervation during this organ's maturation in mice; they have found that striking changes occur in the pattern of innervation deficits in TrkB mutant mice (see p. 4741). During the early postnatal development of these mice, outer hair cell innervation in the apical part of the cochlea fails but nerve fibres in the basal part are maintained. Surprisingly, this innervation pattern is reversed during cochlear maturation, possibly owing to autocrine signalling between neurotrophins and their receptors. The authors suggest that further studies on re-innervating the mature cochlea could lead to new treatments for hearing loss.