Determination of Effective Synaptic Conductances Using Somatic Voltage Clamp

TL;DR

This paper reveals limitations of traditional voltage clamp methods in measuring synaptic conductances, introduces the concept of effective conductance, and proposes a new framework for accurate assessment of synaptic influences on neurons.

Contribution

It identifies the nonlinear interaction issues in traditional conductance measurement and introduces a novel framework to accurately determine effective synaptic conductances.

Findings

Traditional methods can produce significant measurement errors.

Negative conductance values can arise from methodological flaws.

The proposed framework improves accuracy of synaptic conductance estimation.

Abstract

The interplay between excitatory and inhibitory neurons imparts rich functions of the brain. To understand the underlying synaptic mechanisms, a fundamental approach is to study the dynamics of excitatory and inhibitory conductances of each neuron. The traditional method of determining conductance employs the synaptic current-voltage (I-V) relation obtained via voltage clamp. Using theoretical analysis, electrophysiological experiments, and realistic simulations, here we demonstrate that the traditional method conceptually fails to measure the conductance due to the neglect of a nonlinear interaction between the clamp current and the synaptic current. Consequently, it incurs substantial measurement error, even giving rise to unphysically negative conductance as observed in experiments. To elucidate synaptic impact on neuronal information processing, we introduce the concept of effective conductance and propose a framework to determine it accurately. Our work suggests re-examination of previous studies involving conductance measurement and provides a reliable approach to assess synaptic influence on neuronal computation.