Layer specific sub- and suprathreshold coding of voluntary movements in the motor cortex of awake mice

Intracellular recordings of neurons in vivo are becoming routine, yielding rich insights in neural dynamics and the integration of information by neurons under realistic situations. In particular, these methods have been used to estimate the mean excitatory and mean inhibitory conductances experienced by the soma.
We first present a novel method to estimate the effective somatic excitatory and inhibitory conductance as well as their rate and event size from the intracellular in vivo recordings. We apply this technique to the intracellular recordings from the primary motor cortex of awake behaving mice.
Next, we study how dendritic filtering affects these estimates. While the effects of the inputs on the conductance change are mostly local, the effects on the membrane voltage extend further, resulting in the misestimation of the compound excitatory and inhibitory conductances. Using analytical treatment of a simplified model and simulations in a detailed model, we show how much both the mean as well as the variation of the dendritic synaptic conductances are underestimated
by the methods based on conductance measurements at the soma. We discuss the influence of the synaptic distance from the soma on the underestimation for both excitatory as well as inhibitory inputs for different realistic neuronal morphologies.