Continuum of Type I Somatic to Type II Dendritic PRCs; Phase Response Properties of a Morphologically Reconstructed Globus Pallidus Neuron Model

Abstract

A neuron’s phase response curve (PRC) describes how inputs at different times during the spike cycle affect the timing of subsequent spikes, and PRC analysis is a powerful technique for predicting and interpreting the emergence of synchronous modes in coupled networks and neuronal populations. However, neuron models whose PRCs are used to study network dynamics typically consist of a minimal set of dynamic variables and often lack a realistic dendritic structure. In this chapter I describe the phase response properties of a fully reconstructed morphological model of a globus pallidus (GP) neuron during intrinsic pacemaking and during faster spiking driven by somatic current injection. This approach allows investigation of how intrinsic conductances contribute to neuronal responses in a model that preserves the complex staptiotemporal interactions between active properties of the model. I demonstrate that a single neuron can possess both type I and type II PRCs for inputs delivered to different places within the neuronal morphology. Whereas the somatic PRC for the GP model is type I, the distal dendritic PRC is type II as a consequence of the high voltage activated calcium current (CaHVA) and the small conductance calcium-activated potassium current (SK) in distal dendritic segments. The precise shapes of these somatic and dendritic PRCs are highly sensitive to the spike frequency of the model such that during faster spiking the skewness of the primary somatic PRC is reduced, the second-order somatic PRC contains a significant negative lobe, and the negative lobe in the primary dendritic PRC is shifted to the second-order PRC. These results illustrate the complex spatiotemporal interactions of synaptic inputs with intrinsic neuronal mechanisms and highlight the need to consider network connectivity on a scale that distinguishes inputs to different regions of the neuronal morphology.