Opposing Effects of Neuronal Activity on Structural Plasticity.

Michael Fauth,Christian Tetzlaff

doi:10.3389/fnana.2016.00075

Abstract

The connectivity of the brain is continuously adjusted to new environmental influences by several activity-dependent adaptive processes. The most investigated adaptive mechanism is activity-dependent functional or synaptic plasticity regulating the transmission efficacy of existing synapses. Another important but less prominently discussed adaptive process is structural plasticity, which changes the connectivity by the formation and deletion of synapses. In this review, we show, based on experimental evidence, that structural plasticity can be classified similar to synaptic plasticity into two categories: (i) Hebbian structural plasticity, which leads to an increase (decrease) of the number of synapses during phases of high (low) neuronal activity and (ii) homeostatic structural plasticity, which balances these changes by removing and adding synapses. Furthermore, based on experimental and theoretical insights, we argue that each type of structural plasticity fulfills a different function. While Hebbian structural changes enhance memory lifetime, storage capacity, and memory robustness, homeostatic structural plasticity self-organizes the connectivity of the neural network to assure stability. However, the link between functional synaptic and structural plasticity as well as the detailed interactions between Hebbian and homeostatic structural plasticity are more complex. This implies even richer dynamics requiring further experimental and theoretical investigations.

Highlights

Information from the environment leads to the activation of neural subnetworks in the brain
We showed that structural plasticity can be classified into two categories: (i) Hebbian structural plasticity leads to an increase of the number or density of dendritic spines and contacts with axonal boutons during phases of high activity (Figure 2, first column, orange). (ii) When these alterations in activity persist, homeostatic structural plasticity balances these changes by removing synapses (Figure 2, second column, orange) and, after days, even by retracting the dendrites themselves (Figure 2, second column, green)
We showed that there is a strong interaction between structural plasticity and synaptic plasticity

Summary

Introduction

Information from the environment leads to the activation of neural subnetworks in the brain. These variations in the number of synapses seem to depend on changes in the stability of the corresponding dendritic spines and axonal boutons correlated to the actual synaptic efficacy adapted by Hebbian synaptic plasticity.

Results

Conclusion