Sound information is transduced from mechanical vibration to electrical signals in the cochlea and conveyed by the spiral ganglion neurons (SGNs) to the cochlear nucleus (CN) (Nayagam et al., 2011), which in turn project directly or indirectly to all upper nuclei of the central auditory nervous system(Cant and Benson, 2003). As the key cells connecting the peripheral and central auditory systems, SGNs have been widely studied in the field. There are two types of SGNs, including 95% type I SGNs that innervate inner hair cells (IHCs) to transmit auditory information, and 5% type II SGNs that innervate outer hair cells (OHCs) with possible function of nociception (Flores et al., 2015; Kiang et al., 1982; Spoendlin, 1969, 1985). Type I SGNs can be further classified into different subtypes encoding distinct aspects of sound information (Liberman, 1978), which is passed to the CN and further processed throughout the central neural network to form auditory perception. Most studies about SGNs focused in the cochlea, especially about their peripheral terminals (namely the cochlear synapses) and the roles of cochlear synaptopathy in different forms of hearing loss (Fernandez et al., 2015; Kujawa and Liberman, 2015; Liberman et al., 2015; Parthasarathy and Kujawa, 2018; Sergeyenko et al., 2013; Viana et al., 2015). Studies of SGN central terminals (namely the auditory nerve central terminals, or AN synapses for simplicity) focused on morphology in earlier days (Fekete et al., 1984; Rouiller et al., 1986; Rouiller and Ryugo, 1984; Ryugo and Fekete, 1982; Ryugo and Rouiller, 1988; Ryugo et al., 1996; Sento and Ryugo, 1989), and later flourished on synaptic physiology using patch clamp recording in acute brain slices, as reviewed by Manis et al (2011). However, our knowledge remains limited in regard to how information from different subtypes of type I SGNs are transmitted to CN neurons under normal and hearing loss conditions. This review aims to discuss recent progress on the innervation profile of different subtypes of AN synapses onto postsynaptic CN neurons, their distinct physiological properties, the changes during aging, and potential mechanisms underlying age-related hearing loss (ARHL).