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Article

Peter Wenner and Pernille Bülow

Homeostatic plasticity refers to a collection of mechanisms that function to homeostatically maintain some feature of neural function. The field began with the view that homeostatic plasticity exists predominantly for the maintenance of spike rate. However, it has become clear that multiple features undergo some form of homeostatic control, including network activity, burst rate, or synaptic strength. There are several different forms of homeostatic plasticity, which are typically triggered following perturbations in activity levels. Homeostatic intrinsic plasticity (HIP) appears to compensate for the perturbation with changes in membrane excitability (voltage-gated conductances); synaptic scaling is thought to be a multiplicative increase or decrease of synaptic strengths throughout the cell following an activity perturbation; presynaptic homeostatic plasticity is a change in probability of release following a perturbation to postsynaptic receptor activity. Each form of homeostatic plasticity can be different in terms of the mechanisms that are engaged, the feature that is homeostatically regulated, the trigger that initiates the compensation, and the signaling cascades that mediate these processes. Homeostatic plasticity is often described in development, but can extend into maturity and has been described in vitro and in vivo.

Article

Monique Rooney

Melodrama is a mixed or transmedial artform that, having migrated from stage to film, television and digital screens, typically combines plastic arts (tableau, mise en scène, filmic close-up, sculptural poses) with performative arts (stage and screen acting, declamation, singing, orchestral or other music). It emerged first in the 18th century when Jean-Jacques Rousseau wrote and composed his “scène lyrique” Pygmalion, a formally innovative and experimental adaptation of the story from Ovid’s Metamorphoses. In the context of the speculative and neoAristotelian ideas that Rousseau contributed to public debate about the significance of imitation or mimesis in the development of language, Rousseau’s foundational melodrama represented the coming-to-life of Pygmalion’s beloved statue, Galatea, as a mimetic scene in which metamorphosis takes place through the statue’s responsiveness to the artist and vice versa. More than simply a theme, imitation is intrinsic to the musical-dramatic and, thus, transmedial structure of the ur-melodrama, through which the alternation of spoken lyric with musical phrasing was intended to draw attention to the mimetic role of vocal accent within the arrangement. This aesthetic structure opened the possibility of representing a diversity of voices on the metropolitan stage and beyond. Since its Enlightenment-era beginnings, the mixed form of melodrama has persisted even as it has been transformed in its itinerary from the 18th century to the early 21st century, transmedially adapting to new modalities and formats as it has moved from stage to print formats and then to film, television, and digital platforms. The transmedial form and reach of melodrama is discernible in latter-day performance and film, in which the mixed form—particularly vocal accent, melody, and gesture—continue to disrupt normative identities and hegemonic systems.

Article

Euopisthobranchia (Aplysia), Nudipleura (Tritonia, Hermissenda, Pleurobranchaea), and Panpulmonata (Lymnaea, Helix, Limax) gastropod mollusks exhibit a variety of reflex, rhythmic, and motivated behaviors that can be modified by elementary forms of learning and memory. The relative simplicity of their nervous systems and behavioral repertoires has allowed the uncovering of processes of neuronal and synaptic plasticity underlying non-associative learning, such as habituation, sensitization, and different forms of associative learning, such as classical and operant conditioning. Decades of work on these simpler and accessible animal systems have almost uniquely yielded an understanding into the mechanistic basis of learning and memory spanning behavior, neuronal circuitry, and molecules. Given the conservative nature of evolutionary processes, the mechanisms deciphered have also provided valuable insights into the neural basis of learning and memory in other metazoans, including higher vertebrates.

Article

Anthony C. Hackney and Eser Ağgön

Stress is encountered by every individual on a daily basis. Such encounters can be of a negative (distress) or a positive (eustress) nature. Excessive and chronic distress exposure is associated with numerous health problems affecting both physiological and psychological components of a person’s well-being. One mediating aspect of these occurrences is the responses of the neuroendocrine system with the body. Physical activity (i.e., exercise) produces large and dramatic changes in the neuroendocrine system as it serves as a “stressor” to the system. To this end, though, chronic engagement in physical activity leads to exercise training-induced adaptations within the neuroendocrine system that potentiate an individual’s ability to deal with distressful experiences and exposures. Therefore, becoming more physically fit and exercise trained is one potential adjunctive therapy available for clinicians to recommend in the treatment of health problems associated with chronic exposure to distress.

Article

Robert J. McDonald and Ellen G. Fraser

One view of the organization of learning and memory functions in the mammalian brain is that there are multiple learning and memory networks that acquire and store different kinds of information. Each neural network is thought to have a central structure. The hippocampus, amygdala, perirhinal cortex, and dorsal striatum are thought to be central structures for different learning and memory networks important for spatial/relational, emotional, visual objects, and instrumental memory respectively. These central structures are part of a complex network including cortical and subcortical brain regions containing areas important for sensory, motivational, modulatory, and output functions. These networks are thought to encode and store information obtained during experiences via a general plasticity mechanism in which the relationship between synapses in these regions are changed. This view suggests that that memory has a physical manifestation in the brain, which allows for synapses to communicate more effectively as a result of activation. One form of synaptic plasticity called long-term potentiation (LTP) is considered a fundamental form of changes in synaptic efficacy mediating learning and long-term memory functions. One of the biochemical mechanisms for initiating LTP is triggered when a type of glutamate receptor, N-methyl-D-aspartate receptor (NMDAR), found in all of these memory networks is activated and various biochemical pathways that can produce long-term enhancements to the efficacy of that synapse are recruited. NMDAR-mediated LTP processes appear to be important for learning and memory processes in these different networks, but there are clear differences. None of the networks require NMDAR functions during expression of new learning. All the networks required NMDAR function during encoding of new information, except the network centered on perirhinal cortex. Finally, all of the networks required NMDAR-mediated plasticity processes for long-term consolidation of new information, except the one centered on the amygdala.

Article

Jimena Perez-Sanchez and Yves De Koninck

One of the most remarkable properties of neural circuits is the ability to restructure their synaptic connections throughout life. This synaptic plasticity allows neurons to structurally reorganize and adapt their function in response to experience. Among the multiple mechanisms that can modulate this property is synaptic inhibition by gamma-Aminobutyric acid (GABA) and/or glycine ionotropic receptors, which allow the flow of chloride and bicarbonate ions through the membrane. Neurons rely upon tight regulation of intracellular chloride for efficient inhibition through these receptors. The maintenance of chloride gradients is important not only to determine the strength of synaptic inhibition but also to determine its nature. Indeed, this inhibition can be hyperpolarizing or depolarizing, or with no outright change in the membrane potential. Despite the fact that membrane depolarization is commonly associated with excitation, depolarizing GABA/glycine can also produce inhibition, thereby highlighting the dual action of these neurotransmitters. Several considerations must be taken into account in order to allow depolarizing GABA/glycine responses to be excitatory. On the other hand, chloride homeostasis is never steady-state and even small changes of chloride across the membrane can impact the strength of inhibition. This dynamic effect has a direct impact on neuronal excitability and makes its regulation by changes in chloride gradients a highly tunable mechanism. Furthermore, increased excitability may also open a window for system refinement changes, such as synaptic plasticity. Indeed, the regulation of chloride homeostasis may underlie periods of enhanced plasticity, such as during early development. Finally, disruption of chloride gradients arises as a hub for pathology, which is evidenced in multiple disorders in the central nervous system.

Article

Daniel Tomsic and Julieta Sztarker

Decapod crustaceans, in particular semiterrestrial crabs, are highly visual animals that greatly rely on visual information. Their responsiveness to visual moving stimuli, with behavioral displays that can be easily and reliably elicited in the laboratory, together with their sturdiness for experimental manipulation and the accessibility of their nervous system for intracellular electrophysiological recordings in the intact animal, make decapod crustaceans excellent experimental subjects for investigating the neurobiology of visually guided behaviors. Investigations of crustaceans have elucidated the general structure of their eyes and some of their specializations, the anatomical organization of the main brain areas involved in visual processing and their retinotopic mapping of visual space, and the morphology, physiology, and stimulus feature preferences of a number of well-identified classes of neurons, with emphasis on motion-sensitive elements. This anatomical and physiological knowledge, in connection with results of behavioral experiments in the laboratory and the field, are revealing the neural circuits and computations involved in important visual behaviors, as well as the substrate and mechanisms underlying visual memories in decapod crustaceans.

Article

Juha Merilä and Ary A. Hoffmann

Changing climatic conditions have both direct and indirect influences on abiotic and biotic processes and represent a potent source of novel selection pressures for adaptive evolution. In addition, climate change can impact evolution by altering patterns of hybridization, changing population size, and altering patterns of gene flow in landscapes. Given that scientific evidence for rapid evolutionary adaptation to spatial variation in abiotic and biotic environmental conditions—analogous to that seen in changes brought by climate change—is ubiquitous, ongoing climate change is expected to have large and widespread evolutionary impacts on wild populations. However, phenotypic plasticity, migration, and various kinds of genetic and ecological constraints can preclude organisms from evolving much in response to climate change, and generalizations about the rate and magnitude of expected responses are difficult to make for a number of reasons. First, the study of microevolutionary responses to climate change is a young field of investigation. While interest in evolutionary impacts of climate change goes back to early macroevolutionary (paleontological) studies focused on prehistoric climate changes, microevolutionary studies started only in the late 1980s. The discipline gained real momentum in the 2000s after the concept of climate change became of interest to the general public and funding organizations. As such, no general conclusions have yet emerged. Second, the complexity of biotic changes triggered by novel climatic conditions renders predictions about patterns and strength of natural selection difficult. Third, predictions are complicated also because the expression of genetic variability in traits of ecological importance varies with environmental conditions, affecting expected responses to climate-mediated selection. There are now several examples where organisms have evolved in response to selection pressures associated with climate change, including changes in the timing of life history events and in the ability to tolerate abiotic and biotic stresses arising from climate change. However, there are also many examples where expected selection responses have not been detected. This may be partly explainable by methodological difficulties involved with detecting genetic changes, but also by various processes constraining evolution. There are concerns that the rates of environmental changes are too fast to allow many, especially large and long-lived, organisms to maintain adaptedness. Theoretical studies suggest that maximal sustainable rates of evolutionary change are on the order of 0.1 haldanes (i.e., phenotypic standard deviations per generation) or less, whereas the rates expected under current climate change projections will often require faster adaptation. Hence, widespread maladaptation and extinctions are expected. These concerns are compounded by the expectation that the amount of genetic variation harbored by populations and available for selection will be reduced by habitat destruction and fragmentation caused by human activities, although in some cases this may be countered by hybridization. Rates of adaptation will also depend on patterns of gene flow and the steepness of climatic gradients. Theoretical studies also suggest that phenotypic plasticity (i.e., nongenetic phenotypic changes) can affect evolutionary genetic changes, but relevant empirical evidence is still scarce. While all of these factors point to a high level of uncertainty around evolutionary changes, it is nevertheless important to consider evolutionary resilience in enhancing the ability of organisms to adapt to climate change.

Article

Healthy aging is associated with changes in sensory, motor, cognitive, and emotional functions. Such changes depend on various factors. In particular, physical activity not only improves physical and motor but also cognitive and emotional functions. Observational (i.e., associations) and cross-sectional studies generally show a positive effect of regular physical exercise on cognition in older adults. Most longitudinal randomized controlled intervention studies also show positive effects, but the results are inconsistent due to large heterogeneity of methodological setups. Positive changes accompanying physical activity mainly impact executive functions, memory functions, and processing speed. Several factors influence the impact of physical activity on cognition, mainly the type and format of the activity. Strength training and aerobic training yield comparable but also differential benefits, and all should be used in physical activities. Also, a combination of physical activity with cognitive activity appears to enhance its effect on cognition in older age. Hence, such combined training approaches are preferable to homogeneous trainings. Studies of brain physiology changes due to physical activity show general as well as specific effects on certain brain structures and functions, particularly in the frontal cortex and the hippocampus, which are those areas most affected by advanced age. Physical activity also appears to improve cognition in patients with mild cognitive dysfunction and dementia and often ameliorates the disease symptoms. This makes physical training an important intervention for those groups of older people. Apart from cognition, physical activity leads to improvement of emotional functions. Exercise can lead to improvement of psychological well-being in older adults. Most importantly, exercise appears to reduce symptoms of depression in seniors. In future intervention studies it should be clarified who profits most from physical activity. Further, the conditions that influence the cognitive and emotional benefits older people derive from physical activity should be investigated in more detail. Finally, measures of brain activity that can be easily applied should be included as far as possible.

Article

Karim Fouad, Abel Torres-Espín, and Keith K. Fenrich

Spinal cord injury results in a wide range of behavioral changes including impaired motor and sensory function, autonomic dysfunction, spasticity, and depression. Currently, restoring lost motor function is the most actively studied and sought-after goal of spinal cord injury research. This research is rooted in the fact that although self-repair following spinal cord injury in adult mammals is very limited, there can be some recovery of motor function. This recovery is strongly dependent on the lesion size and location as well as on neural activity of denervated networks activated mainly through physical activity (i.e., rehabilitative training). Recovery of motor function is largely due to neuroplasticity, which includes adaptive changes in spared and injured neural circuitry. Neuroplasticity after spinal cord injury is extensive and includes mechanisms such as moderate axonal sprouting, the formation of new synaptic connections, network remapping, and changes to neuron cell properties. Neuroplasticity after spinal cord injury has been described at various physiological and anatomical levels of the central nervous system including the brain, brainstem, and spinal cord, both above and below injury sites. The growing number of mechanisms underlying postinjury plasticity indicate the vast complexity of injury-induced plasticity. This poses important opportunities to further enhance and harness plasticity in order to promote recovery. However, the diversity of neuroplasticity also creates challenges for research, which is frequently based on mechanistically driven approaches. The appreciation of the complexity of neuronal plasticity and the findings that recovery is based on a multitude and interlinked adaptations will be essential in developing meaningful new treatment avenues.

Article

Susan C. P. Renn and Nadia Aubin-Horth

Several species show diversity in reproductive patterns that result from phenotypic plasticity. This reproductive plasticity is found for example in mate choice, parental care, reproduction suppression, reproductive tactics, sex role, and sex reversal. Studying the genome-wide changes in transcription that are associated with these plastic phenotypes will help answer several questions, including those regarding which genes are expressed and where they are expressed when an individual is faced with a reproductive choice, as well as those regarding whether males and females have the same brain genomic signature when they express the same behaviors, or if they activate sex-specific molecular pathways to output similar behavioral responses. The comparative approach of studying transcription in a wide array of species allows us to uncover genes, pathways, and biological functions that are repeatedly co-opted (“genetic toolkit”) as well as those that are unique to a particular system (“genomic signature”). Additionally, by quantifying the transcriptome, a labile trait, using time series has the potential to uncover the causes and consequences of expressing one plastic phenotype or another. There are of course gaps in our knowledge of reproductive plasticity, but no shortage of possibilities for future directions.

Article

The role of experience in brain organization and function can be studied by systematically manipulating developmental experiences. The most common protocols use extremes in experiential manipulation, such as environmental deprivation and/or enrichment. Studies of the effects of deprivation range from laboratory studies in which animals are raised in the absence of sensory or social experiences from infancy to children raised in orphanages with limited caregiver interaction. In both cases there are chronic perceptual, cognitive, and social dsyfunctions that are associated with chronic changes in neuronal structure and connectivity. Deprivation can be more subtle too, such as being raised in a low socioeconomic environment, which is often associated with poverty. Such experience is especially detrimental to language development, which in turn, limits educational opportunities. Unfortunately, the effects of some forms of socioemotional deprivation are often difficult, if not impossible, to ameliorate. In contrast, adding sensory or social experiences can enhance behavioral functions. For example, placing animals in environments that are cognitively, motorically, and/or socially more complex than standard laboratory housing is associated with neuronal changes that are correlated with superior functions. Enhanced sensory experiences can be relatively subtle, however. For example, tactile stimulation with a soft brush for 15 minutes, three times daily for just two weeks in infant rats leads to permanent improvement in a wide range of psychological functions, including motoric, mnemonic, and other cognitive functions. Both complex environments and sensory stimulation can also reverse the negative effects of many other experiences. Thus, tactile stimulation accelerates discharge from hospital for premature human infants and stimulates recovery from stroke in both infant and adult rats. In sum, brain and behavioral functions are exquisitely influenced by manipulation of sensory experiences, especially in development.

Article

Robbin Gibb

The process of brain development begins shortly after conception and in humans takes decades to complete. Indeed, it has been argued that brain development occurs over the lifespan. A complex genetic blueprint provides the intricate details of the process of brain construction. Additional operational instructions that control gene and protein expression are derived from experience, and these operational instructions allow an individual to meet and uniquely adapt to the environmental demands they face. The science of epigenetics provides an explanation of how an individual’s experience adds a layer of instruction to the existing DNA that ultimately controls the phenotypic expression of that individual and can contribute to gene and protein expression in their children, grandchildren, and ensuing generations. Experiences that contribute to alterations in gene expression include gonadal hormones, diet, toxic stress, microbiota, and positive nurturing relationships, to name but a few. There are seven phases of brain development and each phase is defined by timing and purpose. As the brain proceeds through these genetically predetermined steps, various experiences have the potential to alter its final form and behavioral output. Brain plasticity refers to the brain’s ability to change in response to environmental cues or demands. Sensitive periods in brain development are times during which a part of the brain is particularly malleable and dependent on the occurrence of specific experiences in order for the brain to tune its connections and optimize its function. These periods open at different time points for various brain regions and the closing of a sensitive period is dependent on the development of inhibitory circuitry. Some experiences have negative consequences for brain development, whereas other experiences promote positive outcomes. It is the accumulation of these experiences that shape the brain and determine the behavioral outcomes for an individual.

Article

Quentin Gaudry and Jonathan Schenk

Olfactory systems are tasked with converting the chemical environment into electrical signals that the brain can use to optimize behaviors such as navigating towards resources, finding mates, or avoiding danger. Drosophila melanogaster has long served as a model system for several attributes of olfaction. Such features include sensory coding, development, and the attempt to link sensory perception to behavior. The strength of Drosophila as a model system for neurobiology lies in the myriad of genetic tools made available to the experimentalist, and equally importantly, the numerical reduction in cell numbers within the olfactory circuit. Modern techniques have recently made it possible to target nearly all cell types in the antennal lobe to directly monitor their physiological activity or to alter their expression of endogenous proteins or transgenes.

Article

A brain-based approach can provide a framework for intelligence, for integration of biology and cognitive processes that have direct implications for education and brain plasticity. Intelligence is reframed here as a selective cluster of different cognitive processes often localized in broad divisions of the brain. Theories and systems that have guided investigation into the brain mechanisms for cognitive processes are reviewed. The focus is on education and cultural disadvantage, delineating changes in the brain due to learning and its dysfunction. Selected programs for enhancement of neurocognitive abilities are presented. Neuronal changes appear to occur as a consequence of learning throughout life. A brain-based approach not only relates to how intelligence works, but also opens the door to understanding the mind and hence consciousness. One may say that the mind is not an eclectic collection of intellectual functions of the brain. Rather, the ultimate goal of intelligence is to form a better view of self that gives meaning to an individual’s existence.

Article

Michael J. Valenzuela

Cognitive reserve refers to the many ways that neural, cognitive, and psychosocial processes can adapt and change in response to brain aging, damage, or disease, with the overarching effect of preserving cognitive function. Cognitive reserve therefore helps to explain why cognitive abilities in late life vary as dramatically as they do, and why some individuals are brittle to degenerative pathology and others exceptionally resilient. Historically, the term has evolved and at times suffered from vague, circular, and even competing notions. Fortunately, a recent broad consensus process has developed working definitions that resolve many of these issues, and here the evidence is presented in the form of a suggested Framework: Contributors to cognitive reserve, which include environmental exposures that demand new learning and intellectual challenge, genetic factors that remain largely unknown, and putative G × E interactions; mechanisms of cognitive reserve that can be studied at the biological, cognitive, or psychosocial level, with a common theme of plasticity, flexibility, and compensability; and the clinical outcome of (enriched) cognitive reserve that can be summarized as a compression of cognitive morbidity, a relative protection from incident dementia but increased rate of progression and mortality after diagnosis. Cognitive reserve therefore has great potential to address the global challenge of aging societies, yet for this potential to be realized a renewed scientific, clinical, and societal focus will be required.

Article

Gerard Bodeker, Sergio Pecorelli, Lawrence Choy, Ranieri Guerra, and Kishan Kariippanon

The scientific landscape of wellbeing and mental wellness has developed significantly through interdisciplinary cross-pollination by researchers in molecular genetics, neuroscience, sociology, economics, including traditional and complementary medicine. The public health challenge lies in using this diverse body of scientific evidence to reframe wellbeing and mental wellness within a 21st-century global public health framework that incorporates evidence-based modalities alongside Western biomedical practice. Evidence on modalities, case studies, policy examples, and emerging directions in societal objectives in wellbeing and mental wellness are discussed in the context of a way forward that focuses on individual self-care, development of resilience, lifespan pathways for wellbeing, and a different economic calculus in framing public health priorities and policies.

Article

Ski Hunter

Various models and theories of adult development exist but they are more assumptions about development than theories. The most popular age and stage theories have lost favor to contextual theories that put more emphasis on interaction with the environment. It has also become recognized that adults are a diverse group and do not follow universal stages of development. The usefulness of chronological age is also questionable as it does not tell us much about any particular person. Instead, we have to know their concerns and the events they are dealing with, and their dreams and aspirations.

Article

American gymnotiformes and African mormyriformes have evolved an active sensory system using a self-generated electric field as a carrier of signals. Objects polarized by the discharge of a specialized electric organ project their images on the skin where electroreceptors tuned to the time course of the self-generated field transduce local signals carrying information about impedance, shape, size, and location of objects, as well as electrocommunication messages, and encode them as primary afferents trains of spikes. This system is articulated with other cutaneous systems (passive electroreception and mechanoception) as well as proprioception informing the shape of the fish’s body. Primary afferents project on the electrosensory lobe where electrosensory signals are compared with expectation signals resulting from the integration of recent past electrosensory, other sensory, and, in the case of mormyriformes, electro- and skeleton-motor corollary discharges. This ensemble of signals converges on the apical dendrites of the principal cells where a working memory of the recent past, and therefore predictable input, is continuously built up and updated as a pattern of synaptic weights. The efferent neurons of the electrosensory lobe also project to the torus and indirectly to other brainstem nuclei that implement automatic electro- and skeleton-motor behaviors. Finally, the torus projects via the preglomerular nucleus to the telencephalon where cognitive functions, including “electroperception” of shape-, size- and impedance-related features of objects, recognition of conspecifics, perception based decisions, learning, and abstraction, are organized.