Preface As in all sensory systems, olfactory perception is shaped by experience. However, unlike other sensory systems, it is increasingly clear that nearly all components of the olfactory pathway, from olfactory sensory neurons to higher order cortical networks, are malleable. Odor experience shapes olfactory system neurogenesis and survival, membrane excitability, synaptic structure and strength, local circuit activity levels, single-unit receptive fields, and regional network functional connectivity. These learned changes in structure and function of the olfactory pathway contribute to the memory of the odor and its associations. But in addition, they shape the perception of the odor. Through such perceptual learning, odors can become more or less distinct from similar odors, allowing the emergence of important or meaningful odor percepts to emerge from the chemical soup in which we live. In this volume, we bring together a collection of authors that cut across model systems, techniques, levels of analysis, and questions to highlight some important and exciting advances in the area of olfactory memory and perception. The first section includes several chapters focusing on invertebrate models. These models, here specifically Drosophila and honey bees, allow opportunities for both exceptional circuit and molecular dissection of odor memory but also often utilize ethologically relevant stimuli and conditions. The second section emphasizes advances using nonhuman mammalian model systems. This section highlights several important aspects of olfactory memory and perception. First, the olfactory system is plastic from the periphery to the cortex. Traditional views of sensory system plasticity have generally involved a stable periphery, allowing basic representations of sensory input to remain constant, while central cortical circuits supported plasticity required for associating those stable sensory representations with meanings or outcomes. However, as described in several chapters here, plasticity is robust in the olfactory bulb as well as throughout the olfactory pathway. Second, the tool box for changing circuit function in the olfactory system is remarkably large. Synaptic plasticity, neurogenesis, neural membrane plasticity, and anatomical changes are all available to store representations of learned familiar odors and their associations. Importantly, these mechanisms are available across the lifespan, from infancy to adulthood. Third, olfactory memory and perception do not rely simply on the local olfactory circuits, but occur within the context of neuromodulatory, and reciprocal and top-down inputs between olfactory and limbic structures. Finally, it is increasingly apparent that olfactory memory and perception are uniquely sensitive to pathology and disease. This may reflect the fact that olfaction is so dependent on plasticity, or may reflect something special about olfactory system structure and function. The final section focuses on recent advances in human olfactory memory and perception. Over the past several years, major advances have been made in understanding olfaction through the brilliant use of cleverly designed functional magnetic resonance imaging in human subjects. This work, across many labs, has led to a state

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where many of the same questions can be asked using both invasive animal research and functional magnetic resonance imaging human research. Together, we believe this collection of chapters paints a broad picture of the state of the art in olfactory memory and perception. Many other authors, approaches, and concepts could have been included—this is an exciting, growing field. We thank the authors that contributed and thank the editorial staff at Elsevier for helping create this volume. Edi Barkai Donald A. Wilson