RESEARCH HIGHLIGHTS Nature Reviews Neuroscience | AOP, published online 5 June 2013; doi:10.1038/nrn3532 NEURAL CODING Timing is key in the olfactory system In principle, when populations of neurons (PCNs), which are when there was a reasonably long neurons encode sensory information, downstream of OBNs, while optoge- lag between the first and second ... temporal the combination of neurons activated, netically stimulating the OBNs of stimulus, indicating that delayed their rate of firing (rate coding) and channelrhodopsin 2-expressing mice. inhibition or delayed facilitation patterns of the timing of their firing in relation to By varying the order of and time has a role in the generation of order activation in one another (temporal coding) could between (the lag) the presentation sensitivity. the periphery all be used to convey information. The of two spots of light that stimulated Finally, the authors investigated can have an importance of each coding strategy is, different parts of the olfactory bulb, the relative importance of temporal- however, unclear. Now, Uchida and they assessed the sensitivity of PCNs versus rate-coding in different parts important colleagues provide evidence for the to changes in temporal coding. of the olfactory system. A decoding functional involvement of temporal coding in the The authors found that the firing analysis showed that in the olfactory effect on transmission of olfactory information. rates of PCNs were influenced by bulb, the temporal features of neu- the coding Exposure to odours generates both the lag and the order of stimulus ronal firing more accurately predicted specific spatiotemporal patterns of presentation. This indicates that the order of the stimulus presentation of sensory activation in olfactory bulb neurons information about the relative spike than did the firing rate. However, information ... (OBNs). Here, the authors acquired timing in OBNs is transmitted to predictions based on firing rate extracellular recordings from piriform higher-order neurons in the olfactory were more successful in the piriform cortex system. cortex, indicating a progression from What are the mechanisms by temporal- to rate-coding, as informa- which variations in relative tion moves from the periphery to firing times can alter the central brain areas. firing of downstream These findings indicate that neurons? The temporal patterns of activation in authors found the periphery can have an important that the sensi- functional effect on the coding of tivity of many sensory information, at least in the PCNs to the olfactory system. order of Katherine Whalley stimulus presenta- ORIGINAL RESEARCH PAPER Haddad, R. et al. tion was Olfactory cortical neurons read out a relative time only code in the olfactory bulb. Nature Neurosci. 19 May 2013 (doi:10.1038/nn.3407) apparent J. Vallis/NPG NATURE REVIEWS | NEUROSCIENCE VOLUME 14 | JULY 2013 © 2013 Macmillan Publishers Limited. All rights reserved.