The Rewiring Brain

A Computational Approach to Structural Plasticity in the Adult Brain

Arjen van Ooyen, Markus Butz-Ostendorf

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780128037843
• eBook ISBN: 9780128038727
• Topic: Biological Sciences
• Subtopic: Developmental Psychology
• Index: Biological Sciences

The adult brain is not as hard-wired as traditionally thought. By modifying their small- or large-scale morphology, neurons can make new synaptic connections or break existing ones (structural plasticity). Structural changes accompany memory formation and learning, and are induced by neurogenesis, neurodegeneration and brain injury such as stroke.Exploring the role of structural plasticity in the brain can be greatly assisted by mathematical and computational models, as they enable us to bridge the gap between system-level dynamics and lower level cellular and molecular processes. However, most traditional neural network models have fixed neuronal morphologies and a static connectivity pattern, with plasticity merely arising from changes in the strength of existing synapses (synaptic plasticity). In The Rewiring Brain, the editors bring together for the first time contemporary modeling studies that investigate the implications of structural plasticity for brain function and pathology. Starting with an experimental background on structural plasticity in the adult brain, the book covers computational studies on homeostatic structural plasticity, the impact of structural plasticity on cognition and cortical connectivity, the interaction between synaptic and structural plasticity, neurogenesis-related structural plasticity, and structural plasticity in neurological disorders.Structural plasticity adds a whole new dimension to brain plasticity, and The Rewiring Brain shows how computational approaches may help to gain a better understanding of the full adaptive potential of the adult brain. The book is written for both computational and experimental neuroscientists.- Reviews the current state of knowledge of structural plasticity in the adult brain- Gives a comprehensive overview of computational studies on structural plasticity- Provides insights into the potential driving forces of structural plasticity and the functional implications of structural plasticity for learning and memory- Serves as inspiration for developing novel treatment strategies for stimulating functional repair after brain damage

Section II

Homeostatic Structural Plasticity

Outline

Chapter 5 Network Formation Through Activity-Dependent Neurite Outgrowth: A Review of a Simple Model of Homeostatic Structural Plasticity

Chapter 6 Clustered Arrangement of Inhibitory Neurons Can Lead to Oscillatory Dynamics in a Model of Activity-Dependent Structural Plasticity

Chapter 7 A Detailed Model of Homeostatic Structural Plasticity Based on Dendritic Spine and Axonal Bouton Dynamics

Chapter 8 Critical Periods Emerge from Homeostatic Structural Plasticity in a Full-Scale Model of the Developing Cortical Column

Chapter 9 Lesion-Induced Dendritic Remodeling as a New Mechanism of Homeostatic Structural Plasticity in the Adult Brain

Chapter 5

Network Formation Through Activity-Dependent Neurite Outgrowth

A Review of a Simple Model of Homeostatic Structural Plasticity

Arjen van Ooyen, VU University Amsterdam, Amsterdam, The Netherlands

Abstract

Both during development and in adulthood, neurite outgrowth is influenced by neuronal electrical activity. High activity levels suppress outgrowth, and low levels, provided they do not fall below a minimum value, promote outgrowth. In this chapter, I review one of the first models of structural plasticity, devised to unravel the implications of activity-dependent neurite outgrowth. In the model, each neuron has a circular neuritic field, which expands when the neuron’s electrical activity is below a homeostatic set-point and retracts when it is above the set-point. Neurons connect when their neuritic fields overlap. Many interesting phenomena emerge from this simple model. The neurons self-organize into a network via a transient phase of high connectivity before reaching activity homeostasis. At equilibrium, network connectivity is critical and, owing to inhibitory cells, has a clustered structure. Although lacking intrinsic growth differences, excitatory and inhibitory cells differentiate in size. Network connectivity self-repairs following cell loss (stroke) and reorganizes after insertion of new cells (neurogenesis). In addition, the network can produce retinal mosaics and generate developmental transitions in cognition. Together, the results show that homeostatic regulation of activity through activity-dependent neurite outgrowth is a potent driving force for both network development and network reorganization.

Keywords

Homeostasis; structural plasticity; neurite outgrowth; network formation; self-organization; cell differentiation; criticality; hysteresis; retinal mosaics

Outline

1 Introduction 96

2 Model 97

2.1 Overview 97

2.2 Neuron Model 97

2.3 Outgrowth and Connectivity 98

2.4 Parameters 99

3 Results 99

3.1 Network Assembly, Overshoot, and Homeostasis 99

3.2 Relationship Between Activity and Connectivity 101

3.3 Slow Fluctuations in Activity 102

3.4 Effect of Inhibition on Overshoot 103

3.5 Multiple Equilibrium States 103

3.6 Differentiation Between Excitatory and Inhibitory Cells 105

3.7 Patchy Connectivity Structure 107

3.8 Self-Repair of Connectivity After Lesions 107

3.9 Neurogenesis-Induced Network Reorganization 108

3.10 Neuronal Death During Development 108

3.11 Differentiation of Intrinsic Properties 108

3.12 Self-Organized Criticality 108

3.13 Retinal Mosaics 109

3.14 Developmental Changes in Burst Patterns 111

3.15 Developmental Transitions in Cognition 112

4 Discussion 112

4.1 Future Experimental Studies 113

4.2 Future Modeling Studies 114

References 116

1 Introduction

Neuronal electrical activity plays an important role in the development of neurons into neural networks. Many processes that determine network connectivity and neuronal function are, on a variety of time scales and levels of organization, modulated by electrical activity. Cell death, cell differentiation, neurite outgrowth and branching, synapse formation and elimination, and ion channel and neurotransmitter expression are all influenced by electrical activity.^1–3 This activity-dependent maturation begins even before the onset of sensory responses, driven by intrinsically generated patterns of electrical activity.⁴

Electrical activity is a prominent factor not only during development but also in adulthood. Alterations in afferent activity in the mature brain, such as those caused by peripheral or central lesions (retinal lesions or stroke, for example), trigger extensive axon and dendrite remodeling and changes in synapse numbers, leading to massive adaptations in network connectivity.^5–9

This chapter focuses on activity-dependent n...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Editorial
• Section I: Experimental Background
• Section II: Homeostatic Structural Plasticity
• Section III: Structural plasticity and connectivity
• Section IV: Structural Plasticity and Learning and Memory
• Section V: Neurogenesis-Related Structural Plasticity
• Section VI: Structural plasticity and pathology
• Index