The representations of natural sounds in the auditory nervous system are based on dense and redundant temporal and population codes in the first stages of processing, and sparse and highly specific rate and population codes in more central areas. This process of going from more ´literal´ to more ´abstract´ representations is of great interest in computational neuroscience, since it is closely related to how many different percepts are supposed to emerge from a continuous stimulus in our brains.On the other hand, natural sounds have broad band spectra, are highly structured in time and formed by segments with durations of a few seconds. Their temporal representation is based on both phase locking to neuronal firing to the fine structure (carrier frequency) and locking of some neurons to the, slower, amplitude (envelope) modulations. The encoding of envelope modulations is one of the main cues used to extract useful percepts from speech signals. These temporal picture coexist with the, more widely studied, tonotopic organization of all the auditory nuclei.While envelope modulations are encoded in the auditory nerve using solely synchronized spiking (temporal code), several response measures on neurons of the ventral cochlear nucleus (chopper units) have shown enhanced synchonization for a small range of modulation periods only. Therefore, an extra periodotopic (based on temporal information) dimension exists in this neural population, aside of the tonotopic organization inherited from the cochlea. Futhermore, in subsequent stages of processing (central nucleus of the inferior colliculus, upstream in the auditory pathway) the periodotopic information is also expresed in rate response [3].We will critically analyze two recent approaches to this problem, mostly based on simplifiedrealizations of neural networks [1,2], and propose a biologically rooted, dynamically simplified, and hopefully accurate model of envelope encoding in the ventral cochlear nucleus (VCN). In this scheme we combine a highly detailed implementation of the auditory periphery with generic, but channel based, VCN neuron models and a simplified and flexible connectionist framework.Keywords: Auditory system, Temporal coding, . Neural networks.References[1] Dicke U. et al. (2007) A neural circuit transforming temporal periodicity information intoa rate-based representation in the mammalian auditory system. J. Acoust. Soc. Am. 121: 310-326.[2] Guerin A. et al. (2006) Evaluation of two computational models of amplitude modulationcoding in the inferior colliculus. Hearing Research, 211: 54-62.[3] Joris, P. X. et al. (2004) Neural Processing of Amplitude-Modulated Sounds. Physiol Rev84: 541–577, 76