Microglia are largely known as the major orchestrators of the brain inflammatory response. As such, they have been traditionally studied in various contexts of disease, where their activation has been assumed to induce a wide range of detrimental effects. In the last few years, a series of discoveries have challenged the current view of microglia, showing their active and positive contribution to normal brain function. This Research Topic reviewed the novel physiological roles of microglia in the developing, mature and aging brain, under non-pathological conditions. In particular, this Research Topic discussed the cellular and molecular mechanisms by which microglia contribute to the formation, pruning and plasticity of synapses; the regulation of adult neurogenesis as well as hippocampal learning and memory; among other important roles. Because these novel findings defy our understanding of microglial function in health as much as in disease, this Research Topic also summarized the current view of microglial nomenclature, phenotypes, origin and differentiation, and contribution to various brain pathologies. Additionally, novel imaging approaches and molecular tools to study microglia in their non-activated state have been discussed. In conclusion, this Research Topic seeked to emphasize how the current research in neuroscience is challenged by never-resting microglia.

The importance of this unique book's approach lies in addressing the impact of neurobiological factors as well as psychological influences on brain recovery following injury. There is growing evidence that emotional, motivational, and cognitive factors along with personality traits play a crucial role in brain plasticity, resilience, and recovery. Topics include synaptic and neuronal plasticity, development of brain reserves, biological markers, environmental factors, emotional resilience, and personality traits. By combining the latest research on neural mechanisms and psychological resilience the authors present a book that will help lead to the development of better treatment strategies for functional recovery from brain damage. The new edition is fully updated throughout and contains completely new chapters on brain recovery in childhood, epigenetic aspects of brain recovery, and artificial intelligence techniques in traumatic brain injury research.

The brainstem reticular formation is the archaic core of ascending and descending pathways connecting the brain with spinal cord. After the pioneer description of the activating role of the ascending reticular activating system by Moruzzi and Magoun in 1949, an increasing number of studies have contributed to disclose the multifaceted roles of this brain area. In fact, the brainstem reticular formation sub-serves a variety of brain activities such as the modulation of the sleep-waking cycle, the level of arousal and attention, the drive for novelty seeking behaviors and mood. Meanwhile, descending pathways play a key role in posture modulation, extrapyramidal movements, and autonomic functions such as breathing and blood pressure. Moreover, both descending and ascending fibers of the reticular formation are critical in gating the sensory inputs and play a critical role in pain modulation and gaze control. All these activities are impaired when a damage affects critical nuclei of the reticular formation. Remarkably, in neurodegenerative diseases involving reticular nuclei, the rich collaterals interconnecting reticular isodendritic neurons represent a gateway for disease spreading placing the role of the reticular nuclei as a pivot in a variety of brain disorders. The present Research Topic is an updated collection of recent studies, which contribute to define the systematic anatomy of the reticular formation, its physiological and pharmacological features, as well as its involvement in neurodegenerative disorders and neuroprotection.

The term “synaptic plasticity” is a broad concept, which is studied with a variety of experimental approaches. One focus is the impact of changes in synaptic, neuronal and glial morphology on brain circuitry and behavior. In this regard, unique animal models have been key to the study of affective and social behaviors and neurological and psychiatric diseases. However, there is a paucity of compilations directed toward the correlation of alterations in synaptic structure with various physiological and behavioral paradigms. This Frontiers Research Topic will, therefore, serve as an exciting forum for the exchange of novel hypotheses and data and an important resource and reference for investigators studying synaptic and brain plasticity, as well as those in related fields.

This book examines recent key findings on the mechanisms of axonal and dendritic remodeling in different model organisms. Each chapter is contributed by a panel of experts in their respective subfields of neurosciences, to provide and discuss the latest discoveries ranging from neuronal morphogenesis during development, experience-dependent structural plasticity, to neuronal degeneration, regeneration, and pathologies in neurological disorders. The process of neuronal remodeling, specifically their axons and dendrites, is essential for the proper wiring of the nervous system during early development and continues during postnatal ages to shape the pattern of synaptic connections throughout the life of the organism, including humans. Over recent years, substantial progress has been made in our understanding of the cellular and molecular mechanisms that control neuronal remodeling. In addition, there is accumulating evidence demonstrating how the nervous system could remodel in response to injury and in pathological conditions. Topics discussed in the book include: Axonal degeneration during development and in pathological or disease conditions Neuronal morphogenesis (axons and dendrites) Experience-dependent structural plasticity to synaptogenesis Dendrite degeneration and regeneration