Exploring the Depths of Neuronal Dynamics: Simulating 3D Reaction-Diffusion

Published on May 17, 2022

Imagine you’re exploring a vast forest, where each tree represents a unique neuron. To understand the complex activity happening within these neurons, scientists have developed a simulation method that takes into account both the electrical and chemical processes at play. Just like how a tree’s branches extend in all directions, this simulation expands beyond the traditional 1D representation to capture the intricate dynamics that occur when spatial conditions change. By employing an advanced algorithm, researchers have successfully transformed neuron morphologies into consistent 3D regions, allowing for more accurate simulations of reaction-diffusion kinetics. This technique not only considers ion channels and synapses but also factors in dendritic spines and the soma, uncovering hidden details that would be overlooked in a simpler 1D simulation. The methods have been thoroughly tested and validated, demonstrating impressive performance in capturing the nuanced behaviors of neurons and their networks.

Neuronal activity is the result of both the electrophysiology and chemophysiology. A neuron can be well-represented for the purposes of electrophysiological simulation as a tree composed of connected cylinders. This representation is also apt for 1D simulations of their chemophysiology, provided the spatial scale is larger than the diameter of the cylinders and there is radial symmetry. Higher dimensional simulation is necessary to accurately capture the dynamics when these criteria are not met, such as with wave curvature, spines, or diffusion near the soma. We have developed a solution to enable efficient finite volume method simulation of reaction-diffusion kinetics in intracellular 3D regions in neuron and network models and provide an implementation within the NEURON simulator. An accelerated version of the CTNG 3D reconstruction algorithm transforms morphologies suitable for ion-channel based simulations into consistent 3D voxelized regions. Kinetics are then solved using a parallel algorithm based on Douglas-Gunn that handles the irregular 3D geometry of a neuron; these kinetics are coupled to NEURON’s 1D mechanisms for ion channels, synapses, pumps, and so forth. The 3D domain may cover the entire cell or selected regions of interest. Simulations with dendritic spines and of the soma reveal details of dynamics that would be missed in a pure 1D simulation. We describe and validate the methods and discuss their performance.

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