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Neuronal activity patterns contain information in their temporal structure, indicating that information transfer between neurons may be optimized by temporal filtering. In the zebrafish olfactory bulb, subsets of output neurons (mitral cells) engage in synchronized oscillations during odour responses, but information about odour identity is contained mostly in non-oscillatory firing rate patterns. Using optogenetic manipulations and odour stimulation, we found that firing rate responses of neurons in the posterior zone of the dorsal telencephalon (Dp), a target area homologous to olfactory cortex, were largely insensitive to oscillatory synchrony of mitral cells because passive membrane properties and synaptic currents act as low-pass filters. Nevertheless, synchrony influenced spike timing. Moreover, Dp neurons responded primarily during the decorrelated steady state of mitral cell activity patterns. Temporal filtering therefore tunes Dp neurons to components of mitral cell activity patterns that are particularly informative about precise odour identity. These results demonstrate how temporal filtering can extract specific information from multiplexed neuronal codes. Optogenetic stimulation in the zebrafish olfactory bulb and downstream read out of activity in the homologue of olfactory cortex demonstrate how temporal filtering can extract specific components of neuronal codes. Timing as a neuronal filter Neurons in the olfactory bulb of zebrafish and other species respond to odours with complex firing that contains both oscillatory and non-oscillatory components, but the functional importance of these different components is unclear. Using optogenetic stimulation, Rainer Friedrich and colleagues examine directly the downstream readout of oscillatory bulb activity in the posterior zone of the dorsal telencephalon (Dp), a zebrafish homologue of the olfactory cortex. Dp neurons were largely insensitive to synchronized oscillatory activity, but respond to steady-state activity. These findings could be accounted for by low-pass filter-like biophysical properties of Dp neurons, and demonstrate how filtering can extract individual components of neuronal codes., Author(s): Francisca Blumhagen [sup.1] [sup.5] , Peixin Zhu [sup.1] , Jennifer Shum [sup.1] [sup.5] , Yan-Ping Zhang Schärer [sup.1] , Emre Yaksi [sup.2] , Karl Deisseroth [sup.3] , Rainer W. [...]