Active subthreshold dendritic conductances shape the local field potential

TL;DR

This study demonstrates that subthreshold active dendritic conductances, especially I$_{ m h}$, significantly influence local field potentials, affecting their spectral properties and offering insights into dendritic processing through LFP analysis.

Contribution

The paper provides a detailed modeling analysis showing how subthreshold active conductances shape the LFP, highlighting the role of I$_{ m h}$ and distribution effects, which was previously underexplored.

Findings

I$_{ m h}$ conductance causes resonance in LFP spectral density.

Asymmetric synaptic input enhances the effect of active conductances on LFP.

Distribution of conductances near synaptic input strongly influences LFP signals.

Abstract

The main contribution to the local field potential (LFP) is thought to stem from synaptic input to neurons and the ensuing subthreshold dendritic processing. The role of active dendritic conductances in shaping the LFP has received little attention, even though such ion channels are known to affect the subthreshold neuron dynamics. Here we used a modeling approach to investigate the effects of subthreshold dendritic conductances on the LFP. Using a biophysically detailed, experimentally constrained model of a cortical pyramidal neuron, we identified conditions under which subthreshold active conductances are a major factor in shaping the LFP. We found that particularly the hyperpolarization-activated inward current, I$_{\rm h}$, can have a sizable effect and cause a resonance in the LFP power spectral density. To get a general, qualitative understanding of how any subthreshold active dendritic conductance and its cellular distribution can affect the LFP, we next performed a systematic study with a simplified model. We found that the effect on the LFP is most pronounced when (1) the synaptic drive to the cell is asymmetrically distributed (i.e., either basal or apical), (2) the active conductances are distributed non-uniformly with the highest channel densities near the synaptic input, and (3) when the LFP is measured at the opposite pole of the cell relative to the synaptic input. In summary, we show that subthreshold active conductances can be strongly reflected in LFP signals, opening up the possibility that the LFP can be used to characterize the properties and cellular distributions of active conductances.