2010-11-26 at 16:00
UMR 7102 - Neurobiology of Adaptive Processes, University Pierre and Marie Curie, Paris 6, Building B, 5th floor, Room 501 (How to come)
Sodium channel inactivation: an efficient mechanism for temporal coding?
Neurons transmit spikes following an all-or-none principle: an action potential is generated and propagated provided that the stimulus strength is large enough; otherwise the depolarization is not propagated. The minimal stimulus strength above which an action potential is emitted is called the excitability threshold. Recent in vivo experiments in different brain areas have shown that this threshold can be highly variable and adaptive on a fine time scale. This adaptation has been supposed to enhance the selectivity of sensory neurons. More generally, it confirms the importance of spike timing in neural coding.
We have investigated this issue from a biophysical point of view, both theoretically and numerically. First, we have analyzed the different contributions to threshold variability. Interestingly, we have observed that the threshold can be highly variable in detailed models of cortical neuron, and have been able to predict it variations with a simple formula. This led us to focus on the specific role of sodium channel inactivation in synaptic integration. Relying on a dataset on sodium channels, we have confirmed that this last mechanism can be responsible for threshold adaptation in central neurons. Moreover, we have proposed an integrate-and-fire model which takes specifically into account the effect of sodium channel inactivation. This allowed us to study more quantitatively the impact of this mechanism on the transmission of signal fluctuations.