Article Summary

Title : Heterogeneous firing rate response of mouse layer V pyramidal neurons in the fluctuation-driven regime
Authors : Yann Zerlaut, Bartosz Telenczuk, Charlotte Deleuze, Thierry Bal, Gilles Ouanounou and Alain Destexhe
Year : 2016
Journal : The Journal of Physiology
Volume : 594
Pages : 3791-3808


<p> </p> <p class="p1"><span class="s1">Characterizing the input–output properties of neocortical neurons is of crucial importance for understanding the properties emerging at the network level. In the regime of low-rate irregular firing (such as in the <em>awake</em> state), determining those properties for neocortical cells remains, however, both experimentally and theoretically challenging. Here, we studied this problem using a combination of theoretical modelling and <em>in vitro</em> experiments. We first identified, theoretically, three somatic variables that describe the dynamical state at the soma in this <em>fluctuation-driven</em> regime: the mean, standard deviation and time constant of the membrane potential fluctuations. Next, we characterized the firing rate response of individual layer V pyramidal cells in this three-dimensional space by means of perforated-patch recordings and <em>dynamic clamp</em> in the visual cortex of juvenile mice <em>in vitro</em>. We found that individual neurons strongly differ not only in terms of their excitability, but also, and unexpectedly, in their sensitivities to fluctuations. Finally, using theoretical modelling, we attempted to reproduce these results. The model predicts that heterogeneous levels of biophysical properties such as sodium inactivation, sharpness of sodium activation and spike frequency adaptation account for the observed diversity of firing rate responses. Because the firing rate response will determine population rate dynamics during asynchronous neocortical activity, our results show that cortical populations are functionally strongly inhomogeneous in young mouse visual cortex, which should have important consequences on the strategies of cortical computation at early stages of sensory processing.</span></p>