161-180 of 185 Results

Article

Steroids and Plasticity  

Alyssa L. Pedersen and Colin J. Saldanha

Given the profound influence of steroids on the organization and activation of the vertebrate central nervous system (CNS), it is perhaps not surprising that these molecules are involved in processes that restructure the cytoarchitecture of the brain. This includes processes such as neurogenesis and the connectivity of neural circuits. In the last 30 years or so, we have learned that the adult vertebrate brain is far from static; it responds to changes in androgens and estrogens, with dramatic alterations in structure and function. Some of these changes have been directly linked to behavior, including sex, social dominance, communication, and memory. Perhaps the most dramatic levels of neuroplasticity are observed in teleosts, where circulating and centrally derived steroids can affect several end points, including cell proliferation, migration, and behavior. Similarly, in passerine songbirds and mammals, testosterone and estradiol are important modulators of adult neuroplasticity, with documented effects on areas of the brain necessary for complex behaviors, including social communication, reproduction, and learning. Given that many of the cellular processes that underlie neuroplasticity are often energetically demanding and temporally protracted, it is somewhat surprising that steroids can affect physiological and behavioral end points quite rapidly. This includes recent demonstrations of extremely rapid effects of estradiol on synaptic neurotransmission and behavior in songbirds and mammals. Indeed, we are only beginning to appreciate the role of temporally and spatially constrained neurosteroidogenesis, like estradiol and testosterone being made in the brain, on the rapid regulation of complex behaviors.

Article

Stomatogastric Nervous System  

Wolfgang Stein

The crustacean stomatogastric nervous system contains a set of distinct but interacting rhythmic motor circuits that control movements of the foregut. When isolated, these circuits produce activity patterns that are almost perfect replicas of their behavior in vivo. The ease with which distinct circuit neurons are identified, recorded, and manipulated has provided considerable insight into the general principles of how motor circuits operate and are controlled at the cellular level. The small number of relatively large neurons has facilitated several technical advances in neuroscience research and allowed the identification of one of the earliest circuit connectomes. This enabled, for the first time, studies of circuit dynamics using the relationships between all component neurons of a nervous center. A major discovery was that circuits are not dedicated to producing a single neuronal activity pattern, and that the involved neurons are not committed to particular circuits. This flexibility results predominantly from the ability of neuromodulators to change the cellular and synaptic properties of circuit neurons. The relatively unique access to, and detailed documentation of, identified circuit, sensory, and descending pathways has also started new avenues into examining how individual modulatory neurons and transmitters affect their target cells. Groundbreaking experimental and modeling work has further demonstrated that the intrinsic properties of neurons depend on their recent history of activation and that neurons and circuits counterbalance destabilizing influences by compensatory homeostatic regulation of ionic conductances. The stomatogastric microcircuits continue to provide key insight into neural circuit operation in numerically larger and less accessible systems.

Article

Stomatopod Vision  

Thomas W. Cronin, N. Justin Marshall, and Roy L. Caldwell

The predatory stomatopod crustaceans, or mantis shrimp, are among the most attractive and dynamic creatures living in the sea. Their special features include their powerful raptorial appendages, used to kill, stun, or disable other animals (whether predators, prey, or competitors), and their highly specialized compound eyes. Mantis shrimp vision is unlike that of any other animal and has several unique features. Their compound eyes are optically triple, each having three separate regions that produce overlapping visual fields viewing certain regions of space. They have the most diverse set of spectral classes of receptors ever described in animals, with as many as 16 types in a single compound eye. These receptors are based on a highly duplicated set of opsin molecules paired with strongly absorbing photostable filters in some photoreceptor types. The receptor set includes six ultraviolet types, all spectrally distinct, many themselves tuned by photostable filters. There are as many as eight types of polarization receptors of up to three spectral classes (including an ultraviolet class). In some species, two sets of these receptors analyze circularly polarized light, another unique capability. Stomatopod eyes move independently, each capable of visual field stabilization, image foveation and tracking, or scanning of image features. Stomatopods are known to recognize colors and polarization features and evidently use these in predation and communication. Altogether, mantis shrimps have perhaps the most unusual vision of any animal.

Article

Stress and Neuroimmunology  

Eric S. Wohleb

Stress is experienced when stimuli pose a perceived or actual threat to an organism. Exposure to a stressor initiates physiological and behavioral responses that are aimed at restoring homeostasis. In particular, stress activates the hypothalamic-pituitary-adrenal axis, leading to release of glucocorticoids, and engages the autonomic nervous system, causing release of norepinephrine. These “stress hormones” have widespread effects, because most cells express respective receptors that initiate cell-type-specific molecular signaling pathways. In the brain, acute stress promotes neuronal activation, resulting in alertness and adaptive behavioral responses. However, chronic or uncontrolled stress exposure can have deleterious effects on neuronal function, including loss of synaptic connections, which leads to behavioral and cognitive impairments. Stress responses also influence the function of brain-resident microglia and peripheral immune cells that interact with the brain, and alterations in these neuroimmune systems can contribute to the neurobiological and behavioral effects of chronic stress. Ongoing research is aimed at uncovering the molecular and cellular mechanisms that mediate stress effects on neuroimmune systems, and vice versa.

Article

Stress-Modulated Pathways  

Nicolas Rohleder

Stress is a condition or an experience that is pervasive throughout human life. While there are many definitions of stress, a common notion is that stress is processed in the central nervous system and has effects on health that are mediated by stress-modulated pathways. Several brain areas, such as the amygdala and the broader limbic system, are involved in interpreting situations as potentially stressful. The signals of these areas converge in the hypothalamus, which orchestrates peripheral stress-modulated pathways, mainly the hypothalamus-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS). Health effects of stress are mediated by long-term alterations of basic stress system activity, which has downstream effects on pathophysiological pathways such as the inflammatory system.

Article

Suprachiasmatic Nucleus Anatomy, Physiology, and Neurochemistry  

Rae Silver

We live in an approximately 24-hour world and circadian rhythms have evolved to adapt organisms to the opportunities presented by Earth’s 24-hour cycle of light and dark. A “master clock” located in the suprachiasmatic nucleus (SCN) of the brain orchestrates daily rhythms in all manner of behavioral, endocrine, metabolic, autonomic, and homeostatic systems in our bodies. The SCN is comprised of about 20,000 neurons and about one third as many astroglia. How can so few neurons and astroglia guide so many rhythms? How do neurons time out an interval as long as a day? The answers are a case study in understanding how genes within cells, and cells within circuits, function together to perform complex activities and optimize bodily functions. While individual clock cells are found in virtually all bodily tissues, the unique connectome of the SCN, its specialized afferent inputs from the retinohypothalamic tract, and its neural and humoral outputs enable its “babel” of neuronal types to synchronize their activity and signal time to the rest of the body. At the molecular-cellular level, circadian rhythms are regulated by a 24-hour transcriptional–translational feedback loop. At the SCN tissue level, individual SCN neurons coordinate their gene expression and electrical activity, working together in circuits that sustain coherent rhythms. The SCN has many distinct cell types based on their neurotransmitters, neuropeptides, and afferent and efferent connections. There has been much progress in unraveling the dynamic network organization that underlies the SCN network’s communications. Though the precise anatomical connections underlying interneuronal communication in the SCN are not completely understood, key signaling mechanisms that sustain the SCN’s intrinsic rhythmicity have been tackled using intersectional genomic tools. Transgenic animals that permit the visualization of clock gene–protein expression have enabled analysis of SCN network activity over time. Availability of animals bearing mutations in clock genes or proteins enable the determination of changes within neurons, among neurons in networks, and their impact on behavior. The use of continuous readouts of circadian activity that track behavior, or clock gene expression, or electrical activity changes over time, within an SCN or a single neuron, leads the way to unraveling mechanisms sustaining the circadian timing system. Because the results of circadian studies generate huge amounts of data, the entry of mathematical modelers and statisticians into the field has begun to yield useful and testable predictions on how these multiplexed systems work to adapt to our 24-hour world.

Article

Synaptic Properties of Sensory Thalamus  

Martha E. Bickford

Detailed studies of thalamic circuits have revealed many features that are shared across nuclei. For example, glutamatergic inputs to the thalamus can be placed into three categories based on the size of the synaptic terminals they form, their synaptic arrangements, and the postsynaptic responses they elicit. Remarkably, these three categories can be identified in most sensory nuclei of the dorsal thalamus. Likewise, in most sensory thalamic nuclei, circuits that release the neurotransmitter gamma aminobutyric acid (GABA) can be placed into two general categories based on their dendritic or axonal origins. Finally, similar cholinergic circuits have been identified across thalamic nuclei. The ultimate goal of examining the shared versus diverse features of thalamic circuits is to identify fundamental modules, mechanisms, and/or conceptual frameworks, in order to decipher thalamic function.

Article

Synesthesia and Sensory Processing  

Louisa J. Rinaldi

Synesthesia is a neurodevelopmental condition that causes 4.4% of the population to experience the world differently. For these individuals certain stimuli (e.g., letters of the alphabet) trigger a secondary experience (e.g., color perception). This process is automatic and remains consistent over time. Tests for measuring synesthesia have successfully built on this principle of synesthetic associations being consistent over time, and using this method a number of studies have investigated the heritability of the condition, cognitive differences that synesthetes have compared with non-synesthetes, and the neurological architecture of synesthete brains. These measures have largely focused on adult synesthetes for whom the condition is already fully developed. Since 2009 researchers have begun to also investigate childhood synesthesia, which has helped to advance our understanding of how this condition emerges. Drawing on both adult and child studies, we can better understand the neurological and cognitive implications of a lifetime of experiencing synesthetic associations.

Article

Taste Buds and Gustatory Transduction: A Functional Perspective  

Alan C. Spector and Susan P. Travers

Everything a person swallows must pass a final chemical analysis by the sensory systems of the mouth; of these, the gustatory system is cardinal. Gustation can be heuristically divided into three basic domains of function: sensory-discriminative (quality and intensity), motivational/affective (promote or deter ingestion), and physiological (e.g., salivation and insulin release). The signals from the taste buds, transmitted to the brain through the sensory branches of cranial nerves VII (facial), IX (glossopharyngeal), and X (vagal), subserve these primary functions. Taste buds are collections of 50–100 cells that are distributed in various fields in the tongue, soft palate, and throat. There are three types of cells that have been identified in taste buds based on their morphological and cytochemical expression profiles. Type II cells express specialized G-protein-coupled receptors (GPCR or GPR) on their apical membranes, which protrude through a break in the oral epithelial lining called the taste pore, that are responsible for the sensing of sweeteners (via the taste type 1 receptor (T1R) 2 + T1R3), amino acids (via the T1R1+T1R3), and bitter ligands (via the taste type 2 receptors (T2Rs)). Type III cells are critical for the sensing of acids via the otopetrin-1 (Otop-1) ion channel. The sensing of sodium, in at least rodents, occurs through the epithelial sodium channel (ENaC), but the exact composition of this channel and the type of taste cell type in which the functional version resides remains unclear. It is controversial whether Type I cells, which have been characterized as glial-like, are involved in sodium transduction or play any taste signaling role. For the most part, receptors for different stimulus classes (e.g., sugars vs. bitter ligands) are not co-expressed, providing significant early functionally related segregation of signals. There remains a persistent search for yet to be identified receptors that may contribute to some functions associated with stimuli representing the so-called basic taste qualities—sweet, salty, sour, bitter, and umami—as well as unconventional stimuli such as fatty acids (in addition to cluster of differentiation-36 (CD-36), GPR40, and GPR120) and maltodextrins. The primary neurotransmitter in taste receptor cells is ATP, which is released through a voltage-gated heteromeric channel consisting of the calcium homeostasis modulator 1 and 3 (CALHM1/3) and binds with P2X2/X3 receptors on apposed afferent fibers. Serotonin released from Type III cells has been implicated as an additional neurotransmitter, binding with HT3a receptors, and possibly playing a role in acid taste (which is sour to humans). Taste bud cells undergo complete turnover about every two weeks. Although there remains much to be understood about the operations of the taste bud, perhaps the one very clear principle that emerges is that the organization of signals transmitted to the brain is not random and arbitrary to be decoded by complex algorithms in the circuits of the central gustatory system. Rather, the transmission of taste information from the periphery is highly ordered.

Article

Thalamocortical Interactions for Sensory Processing  

Jose M. Alonso and Harvey A. Swadlow

The thalamocortical pathway is the main route of sensory information to the cerebral cortex. Vision, touch, hearing, taste, and balance all depend on the integrity of this pathway that connects the thalamic structures receiving sensory input with the cortical areas specialized in each sensory modality. Only the ancient sense of smell is independent of the thalamus, gaining access to cortex through more anterior routes. While the thalamocortical pathway targets different layers of the cerebral cortex, its main stream projects to the middle layers and has axon terminals that are dense, spatially restricted, and highly specific in their connections. The remarkable specificity of these thalamocortical connections allows for a precise reconstruction of the sensory dimensions that need to be most finely sampled, such as spatial acuity in vision and sound frequency in hearing. The thalamic axon terminals also segregate topographically according to their stimulus preferences, providing a simple principle to build cortical sensory maps: neighboring values in sensory space are represented by neighboring points within the cortex. Thalamocortical processing is not static. It is continuously modulated by the brain stem and corticothalamic feedback based on the level of attention and alertness, and during sleep or general anesthesia. When alert, visual thalamic responses become stronger, more reliable, more sustained, more effective at sampling fast changes in the scene, and more linearly related to the stimulus. The high firing rates of the alert state make thalamocortical synapses chronically depressed and excitatory synaptic potentials less dependent on temporal history, improving even further the linear relation between stimulus and response. In turn, when alertness wanes, the thalamus reduces its firing rate, and starts generating spike bursts that drive large postsynaptic responses and keep the cortex responsive to sudden stimulus changes.

Article

The Neuroendocrinology of Empathy  

James Burkett and Farzaneh Naghavi

“Empathy” is an umbrella term for any type of process in which one is affected by the emotional state of others, and it is of great importance for daily social interaction. Empathic processes are thought to have evolved in the context of parental care to motivate caregivers to respond to helpless neonates’ needs, but over time may have been generalized outside the rearing context to make a wider social network and help shape social behaviors. It is becoming more apparent that in several psychiatric disorders, such as major depressive disorder, autism spectrum disorder, and antisocial personality disorder, impaired empathic behaviors are correlated with the severity of the disease and a reduced quality of life. Therefore, developing scientific avenues for the study of empathy, its mechanisms, and origins is important for human health and understanding the human condition.

Article

The Regulation of Sleep  

Craig Heller

The words “regulation” and “control” have different meanings. A rich literature exists on the control mechanisms of sleep—the genomic, molecular, cellular, and circuit processes responsible for arousal state changes and characteristics. The regulation of sleep refers to functions and homeostatic maintenance of those functions. Much less is known about sleep regulation than sleep control, largely because functions of sleep are still unknown. Regulation requires information about the regulated variable that can be used as feedback information to achieve optimal levels. The circadian timing of sleep is regulated, and the feedback information is entraining stimuli such as the light–dark cycle. Sleep itself is homeostatically regulated, as evidenced by sleep deprivation experiments. Eletroenceophalography (EEG) slow-wave activity (SWA) is regulated, and it appears that adenosine is the major source of feedback information, and that fact indicates an energetic function for sleep. The last aspect of sleep regulation discussed in this short article is the non-rapid eye movement (NREM) and rapid eye movement (REM) sleep cycling. Evidence is discussed that supports the argument that NREM sleep is in a homeostatic relationship with wake, and REM sleep is in a homeostatic relationship with NREM sleep.

Article

Thirst and Water Balance  

Derek Daniels

Maintaining water balance is critical for survival, but our bodies are constantly losing more water than we produce. Consuming water, therefore, is needed to restore what is lost by sweating, bleeding, vomiting, urinating, even breathing. Because the fluid in the body is divided into intracellular and extracellular compartments, and because depletion can happen in one compartment without affecting the other, separate detection mechanisms for losses in each are required. Moreover, the relatively high concentration of sodium in the extracellular space means that sodium loss accompanies extracellular dehydration. Accordingly, the behavioral response to loss of fluid from the extracellular space needs to include sodium intake. Activity of osmoreceptors (in the case of intracellular loss), or baroreceptors and the renin-angiotensin system (in the case of extracellular loss), underlies the responses to perturbations of fluid balance, and promotes the appropriate behaviors needed to restore balance to the system. The peptide angiotensin II (AngII) is a key component of these responses. Studies of AngII in drinking have been critical in our understanding of how a peripherally derived peptide can act in the brain without transport across the blood–brain barrier, and AngII-induced drinking has served as an important model for the study of intracellular signaling pathways that affect behavior. Although much has been discovered about these systems and how they respond to fluid deficits, the precise means by which the systems generate a behavioral response and the mechanism that mediates satiety remains poorly understood. Nevertheless, ongoing experiments on these open questions have already started to provide a new perspective on the negative reinforcement that is provided by drinking under conditions of thirst.

Article

Transcriptional Regulation Underlying Long-Term Sensitization in Aplysia  

Robert J. Calin-Jageman, Theresa Wilsterman, and Irina E. Calin-Jageman

The induction of a long-term memory requires both transcriptional change and neural plasticity. Many of the links between transcription and memory have been revealed through the study of long-term sensitization in the Aplysia genus of marine mollusks. Sensitization is a conserved, non-associative form of pain memory in which a painful stimulus produces an increase in arousal and defensive behavior. The neural circuits that help encode sensitization memory are well characterized, and sensitization can be simulated in neuronal cell cultures. One feature of sensitization in Aplysia is that only some training protocols initiate transcription and produce long-term memory; others produce only short-term memories. This occurs because the induction of long-term sensitization requires the activation of two signal-transduction pathways that regulate transcription: (a) a fast but transient activation of the cAMP/PKA pathway that activates the transcription factor CREB1 and (b) a delayed activation of the ERK isoform of MAPK that deactivates the transcriptional repressor CREB2. The effectiveness of different training protocols is based on the synchronization of these pathways. The cAMP/PKA and MAPK pathways are complex, involving extracellular and trans-synaptic signaling, feedback loops, and crosstalk. It has proven possible to model transcriptional activation with enough fidelity to generate in silico predictions for optimized learning, which has been validated in cell cultures and intact animals. Training protocols that successfully activate CREB1 while deactivating CREB2 produce a complex transcriptional cascade that helps encode long-term sensitization memory. The transcriptional cascade involves a focused wave of immediate-early transcriptional activations. This includes the activation of additional transcription factors, such as C/EBP, as well as effectors such as uch, sensorin, and tolloid/BMP-1. These early transcriptional changes close feedback loops that help extend and stabilize the early wave of transcriptional changes, triggering a broader late wave of transcriptional changes likely to alter neural signaling, increase protein production, transport mRNAs, and induce meta-plasticity. A small set of transcripts participate in both the early and late waves, and several of these (CREB1, synataxin, eIF4) play essential roles in completing the induction of long-term sensitization. Most transcriptional changes fade as sensitization memory is forgotten, but some changes persist beyond forgetting, including a long-lasting up-regulation of an inhibitory peptide transmitter that could foster forgetting. The maintenance of long-term sensitization may involve self-sustaining transcriptional feedback loops. In particular, CREB1 binds to its own promoter, producing a long-lasting increase in CREB1 mRNA, protein, and gene activation that is essential for sustaining cellular correlates of sensitization for at least 1 day after induction. Many aspects of the induction, stabilization, and maintenance of sensitization memory in Aplysia are conserved, suggesting that it will continue to be a fruitful, simpler system for understanding the physical basis of lasting memory.

Article

Transcriptomic Architecture of Reproductive Plasticity  

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

Understanding How Humans Learn and Adapt to Changing Environments  

Daphne Bavelier and Aaron Cochrane

Compared to other animals or to artificial agents, humans are unique in the extent of their abilities to learn and adapt to changing environments. When focusing on skill learning and model-based approaches, learning can be conceived as a progression of increasing, then decreasing, dimensions of representing knowledge. First, initial learning demands exploration of the learning space and the identification of the relevant dimensions for the novel task at hand. Second, intermediate learning requires a refinement of these relevant dimensions of knowledge and behavior to continue improving performance while increasing efficiency. Such improvements utilize chunking or other forms of dimensionality reduction to diminish task complexity. Finally, late learning ensures automatization of behavior through habit formation and expertise development, thereby reducing the need to effortfully control behavior. While automatization greatly increases efficiency, there is also a trade-off with the ability to generalize, with late learning tending to be highly specific to the learned features and contexts. In each of these phases a variety of interacting factors are relevant: Declarative instructions, prior knowledge, attentional deployment, and cognitive fitness have unique roles to play. Neural contributions to processes involved also shift from earlier to later points in learning as effortfulness initially increases and then gives way to automaticity. Interestingly, video games excel at providing uniquely supportive environments to guide the learner through each of these learning stages. This fact makes video games a useful tool for both studying learning, due to their engaging nature and dynamic range of complexity, as well as engendering learning in domains such as education or cognitive training.

Article

Urochordate Nervous Systems  

Kerrianne Ryan and Ian A. Meinertzhagen

Urochordates are chordate siblings that comprise the following marine invertebrates: the sessile Ascidiaceae, or sea squirts; planktonic Larvacea; and the pelagic salps, doliolids, and pyrosomes (collectively the Thaliacea), each more beautiful than the next. Tadpole larvae of ascidians and adult larvaceans both have a body plan that is chordate, with a notochord and dorsal, tubular nervous system that forms from a neural plate. Thalaciacea have a ganglion developed from a tubular structure, which has been compared to the vertebrate mes-metencephalic region, and while salps have well developed eyes, other anterior brain components are absent, and the connections within their central nervous system, as well as the neurobiology of other Thaliacea are all little reported. The ascidian tadpole larva is extensively reported, especially in the model species Ciona intestinalis, as is the caudal nerve cord in the larvacean Oikopleura dioica. Chordate features that share proposed homology with vertebrate features include ciliary photoreceptors that hyperpolarize to light, descending decussating motor pathways that resemble Mauthner cell pathways, coronet cells in the ascidian larva and saccus vasculosus of fishes, the neural canal’s Reissner’s fiber; secondary mechanoreceptors that resemble hair cells; and ascidian bipolar cells that are like dorsal root ganglion cells.

Article

Using Neural Stem Cells to Enhance Repair and Recovery of Spinal Circuits After Injury  

Itzhak Fischer and Shaoping Hou

Spinal cord injury is characterized by a complex set of events, which include the disruption of connectivity between the brain and the periphery with little or no spontaneous regeneration, resulting in motor, sensory and autonomic deficits. Transplantation of neural stem cells has the potential to provide the cellular components for repair of spinal cord injury (SCI), including oligodendrocytes, astrocytes, and neurons. The ability to generate graft-derived neurons can be used to restore connectivity by formation of functional relays. The critical requirements for building a relay are to achieve long-term survival of graft-derived neurons and promote axon growth into and out of the transplant. Recent studies have demonstrated that mixed populations of glial and neuronal progenitors provide a permissive microenvironment for survival and differentiation of early-stage neurons, but inclusion of growth factors with the transplant or cues for directional axon growth outside the transplant may also be needed. Other important considerations include the timing of the transplantation and the selection of a population of neurons that maximizes the effective transmission of signals. In some experiments, the essential neuronal relay formation has been developed in both sensory and motor systems related to locomotion, respiration, and autonomic functions. Despite impressive advances, the poor regenerative capacity of adult CNS combined with the inhibitory environment of the injury remain a challenge for achieving functional connectivity via supraspinal tracts, but it is possible that recruitment of local propriospinal neurons may facilitate the formation of relays. Furthermore, it is clear that the new connections will not be identical to the original innervation, and therefore there needs to be a mechanism for translating the resulting connectivity into useful function. A promising strategy is to mimic the process of neural development by exploiting the remarkable plasticity associated with activity and exercise to prune and strengthen synaptic connections. In the meantime, the sources of neural cells for transplantation are rapidly expanding beyond the use of fetal CNS tissue and now include pluripotent ES and iPS cells as well as cells obtained by direct reprogramming. These new options can provide considerable advantages with respect to preparation of cell stocks and the use of autologous grafting, but they present challenges of complex differentiation protocols and risks of tumor formation. It is important to note that although neural stem cell transplantation into the injured spinal cord is primarily designed to provide preclinical data for the potential treatment of patients with SCI, it can also be used to develop analogous protocols for repair of neuronal circuits in other regions of the CNS damaged by injury or neurodegeneration. The advantages of the spinal cord system include well-defined structures and a large array of quantitative functional tests. Therefore, studying the formation of a functional relay will address the fundamental aspects of neuronal cell replacement without the additional complexities associated with brain circuits.

Article

Vision and Art  

Bevil R. Conway

The premise of the field of vision and art is that studies of visual processing can inform an understanding of visual art and artistic practice, and a close reading of art, art history, and art practice can help generate hypotheses about how vision works. Paraphrasing David Hubel, visual neurobiology can enhance art just as knowledge of bones and muscles has for centuries informed artistic representations of the body. The umbrella of visual art encompasses a bewildering diversity of works. A focus on 2-dimensional artworks provides an introduction to the field. For each of the steps taken by the visual brain to turn retinal images into perception, one can ask how the biology informs one’s understanding of visual art, how visual artists have exploited aspects of how the brain processes visual information, and what the strategies deployed by visual artists reveal about neural mechanisms of vision.

Article

Visual Attention  

Sabine Kastner and Timothy J. Buschman

Natural scenes are cluttered and contain many objects that cannot all be processed simultaneously. Due to this limited processing capacity, neural mechanisms are needed to selectively enhance the information that is most relevant to one’s current behavior and to filter unwanted information. We refer to these mechanisms as “selective attention.” Attention has been studied extensively at the behavioral level in a variety of paradigms, most notably, Treisman’s visual search and Posner’s paradigm. These paradigms have also provided the basis for studies directed at understanding the neural mechanisms underlying attentional selection, both in the form of neuroimaging studies in humans and intracranial electrophysiology in non-human primates. The selection of behaviorally relevant information is mediated by a large-scale network that includes regions in all major lobes as well as subcortical structures. Attending to a visual stimulus modulates processing across the visual processing hierarchy with stronger effects in higher-order areas. Current research is aimed at characterizing the functions of the different network nodes as well as the dynamics of their functional connectivity.