[Paper Review] A Neural-Astrocytic Network Architecture: Astrocytic calcium waves modulate synchronous neuronal activity

Ioannis Polykretis, Vladimir A. Ivanov+1 more|arXiv (Cornell University)|Jul 5, 2018

Neural dynamics and brain function85 references3 citations

TL;DR

This paper proposes a biophysically realistic astrocytic model that simulates intracellular calcium waves propagating across subcellular compartments, demonstrating how these waves modulate synchronous neuronal activity through gliotransmission. The model reveals a calcium cascade mechanism that enables astrocytes to regulate neural synchronization, offering a novel computational role for non-neuronal cells in neural-astrocytic networks (NANs).

ABSTRACT

Understanding the role of astrocytes in brain computation is a nascent challenge, promising immense rewards, in terms of new neurobiological knowledge that can be translated into artificial intelligence. In our ongoing effort to identify principles endow-ing the astrocyte with unique functions in brain computation, and translate them into neural-astrocytic networks (NANs), we propose a biophysically realistic model of an astrocyte that preserves the experimentally observed spatial allocation of its distinct subcellular compartments. We show how our model may encode, and modu-late, the extent of synchronous neural activity via calcium waves that propagate intracellularly across the astrocytic compartments. This relationship between neural activity and astrocytic calcium waves has long been speculated but it is still lacking a mechanistic explanation. Our model suggests an astrocytic "calcium cascade" mechanism for neuronal synchronization, which may empower NANs by imposing periodic neural modulation known to reduce coding errors. By expanding our notions of information processing in astrocytes, our work aims to solidify a computational role for non-neuronal cells and incorporate them into artificial networks.

Motivation & Objective

• To develop a biophysically realistic model of astrocytes that preserves spatial compartmentalization of subcellular structures.
• To investigate how intracellular calcium waves in astrocytes modulate synchronous neuronal activity.
• To establish a mechanistic link between neuronal activity and astrocytic calcium signaling for use in artificial intelligence.
• To integrate astrocytes into neural-astrocytic networks (NANs) to enhance computational capabilities beyond traditional neural networks.

Proposed method

• Develops a compartmentalized astrocytic model with distinct subcellular regions reflecting experimental morphology.
• Simulates calcium dynamics using biophysically informed equations to capture wave propagation across astrocytic processes.
• Applies stimulation patterns within the biological range to elicit medium-scale and global calcium waves.
• Models gliotransmission as a mechanism through which calcium waves influence synaptic activity in neurons.
• Validated wave propagation patterns against recent experimental findings on calcium wave types (medium-scale and global).
• Integrates the astrocytic model into a neural-astrocytic network (NAN) framework to explore computational roles in synchronization.

Experimental results

Research questions

• RQ1 How do calcium waves propagate across astrocytic subcompartments in a biologically realistic model?
• RQ2 What functional role do astrocytic calcium waves play in modulating synchronous neuronal activity?
• RQ3 Can a calcium cascade mechanism in astrocytes explain neuronal synchronization observed in experiments?
• RQ4 How might astrocytic calcium dynamics contribute to information processing in artificial neural networks?
• RQ5 What computational advantages does incorporating astrocytes bring to brain-morphic and non-Von Neumann computing architectures?

Key findings

• The model successfully reproduces medium-scale calcium waves propagating toward thick astrocytic branches and full-scale global waves reaching the soma.
• Calcium wave propagation is consistent with experimental observations of both local and network-scale calcium signaling in astrocytes.
• The model demonstrates that synaptic-induced calcium waves can modulate silent neurons via gliotransmission, depending on wave extent.
• Astrocytic calcium waves are shown to impose periodic neural modulation, which may reduce coding errors and enhance synchronization.
• The findings support a functional role for astrocytes in regulating neuronal network dynamics through calcium-mediated signaling.
• The study provides a mechanistic explanation for long-speculated links between neuronal activity and astrocytic calcium waves, advancing NAN-based computation.