The nervous system must adapt its circuits to a constantly changing environment while maintaining a level of stability necessary for coherent behaviour and individual identity. To achieve this, the brain continually adjusts organization and strength of its neuronal connections, a phenomenon known as `synaptic plasticity'. Because the organisation and function of the brain evolves during development and with ageing, and may have to cope with neurological disorders, it is likely that the need for plasticity and/or stability evolves as well throughout life. For instance, initial brain development and learning requires synapse formation, elimination and long-term plasticity, whereas stable information storage and stereotyped behaviours require circuit constancy in the form of stable, enduring and homeostatic synaptic networks. How this balance translates at the level of single synapses, neurons and circuits remains to be fully understood. Since the concept of homeostatic synaptic plasticity has emerged in the late 90's, a surge of studies has highlighted the complexity of the underlying mechanisms, which involve both neurons and glial cells. Moreover, the role of homeostatic plasticity in processes such as memory consolidation during sleep, the refinement of developing circuits and the progression of neurological disorders is just starting to be understood. Many questions remain to be addresssed, such as: 1) Can we organize the many molecules and signalling pathways required for homeostatic synaptic plasticity in a hierarchy? 2) How do brain circuits cooperate at the neuronal and synaptic level to produce homeostatic responses appropriate for information storage? 3) What functions do the many different types of homeostatic plasticity serve and how do they interact with Hebbian synaptic plasticity? 4) What is the implication of homeostatic processes in the etiology and development of neurological disorders such as autism spectrum disorder and Alzheimer?

The aim of this Research Topic (research articles and reviews) is to explore recent advances in our understanding of the cellular and molecular mechanisms that drive homeostatic synaptic processes and how they contribute to the development and physiopathology of neural circuits. We are keen to consider work exploring homeostatic processes on different organism models and different physiological or pathological contexts.

Keywords: homeostatic synaptic plasticity, synaptic scaling, glia, adaptation, neurological disorders

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