Home Research Project Details B2 - Organization of temporal coding in the Xenopus olfactory system
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B2 - Organization of temporal coding in the Xenopus olfactory system

Detlev Schild and Fred Wolf

Odours are detected by olfactory sensory neurons (OSNs), which send their axons to the glomeruli of the olfactory bulb. Here OSNs synapse upon dendrites of mitral cell dendrites whereby a number of 5 to 25 MCs enter in every glomerulum. It is now generally accepted that OSNs decompose odorants into odorant features and that these are projected onto the olfactory bulb. Odours thereby generate spatio-temporal activity patterns in the MCs of the OB, which can be regarded as neuronal odour images. As the perception of an odour or a behavioural response to it takes a rather short time (a few hundred ms), it is conceivable that the olfactory system may use a spike latency code, that is known to carry substantial information in the relative timings of the first stimulus driven spikes. Based on our finding that MC spikes in Xenopus olfactory bulb can be optically recorded as discrete jumps in [Ca2+] fluorescence (Chen et al. 2006, Lin et al. 2007), we succeeded in simultaneously optically recording the spiking activity of more than a dozen MCs with ms temporal resolution. Our data indicate that the relative delays between stimulus and MC spikes in fact appear to bear odour information. Additional evidence that OB output may use a temporal coding scheme is provided by our demonstration that MCs fire in tightly synchronized groups upon odour presentation (Chen et al. 2009, Junek et al. 2009).

In this project, we utilize these advances to quantitatively characterize the properties of spike latency coding in the Xenopus OB and to study its origin in the OB network dynamics. To this end we characterize the spike timing response properties of groups of MCs to individual odorants and binary mixtures of odorants. In particular, we will explore how temporal features of odour representations change when a binary mixture is modified such that dominance shifts from one of the two components to the other. Key features of spike timing assessed by optical recording will be verified by targeted electrical recordings (cell attached). Based on the accumulating data we will use statistical and information theoretical measures to quantify the information content of the relative spike timing in different size groups of MCs. Building on our previous work on the dynamics of spiking neuronal networks (Timme et al. 2008, Timme et al. 2006, Zumdieck et al. 2004), we will use simplified models of OB network dynamics to study which neuronal interactions can generate, preserve and limit the ability of MC neurons to temporally encode stimulus information. In parallel, we will perform simultaneous recording of OSNs firing patterns in response to the same sets of odorant stimuli. OSNs firing patterns will be assessed by (i) optical recording in the olfactory epithelium to determine potentially existing temporal correlations among OSNs and by (ii) optical recording of presynaptic activity in OB glomeruli to precisely characterize the nature of input activity to the OB. In particular the later measurements will be critical to assess to which degree coincidence detection at the level of glomerular processing may contribute to latency coding at the MC level.

Belongs to Group(s):
Neurophysiology of the olfactory system, Theoretical Neurophysics

Is part of  Section B 

Members working within this Project:
Engelken , Rainer J. 
Wolf, Fred 
Schild, Detlev 

Selected Publication(s):

Kludt, E, Okom, C, Brinkmann, A, and Schild, D (2015).
Integrating Temperature with Odor Processing in the Olfactory Bulb
Journal of Neuroscience 35(20):7892-7902.

Martinelli, E, Magna, G, Polese, D, Vergara, A, and Schild, D (2015).
Stable Odor Recognition by a neuro-adaptive Electronic Nose
Scientific Reports 5(Article number: 10960).

Monteforte, M, and Wolf, F (2012).
Dynamic Flux Tubes Form Reservoirs of Stability in Neuronal Circuits
Physical Review X 2(041007):1-12.

Junek, S, Kludt, E, Wolf, F, and Schild, D (2010).
Olfactory Coding with Patterns of Response Latencies
Neuron 67:872-884.

Junek, S, Kludt, E, Wolf, F, and Schild, D (2010).
Olfactory Coding with Patterns of Response Latencies
Neuroforum 16(4):277.

Monteforte, M, and Wolf, F (2010).
Dynamical Entropy Production in Spiking Neuron Networks in the Balanced State
Physical Review Letters 105(26):268104.