21-40 of 152 Results

Article

James S.H. Wong and Catharine H. Rankin

The nematode, Caenorhabditis elegans (C. elegans), is an organism useful for the study of learning and memory at the molecular, cellular, neural circuitry, and behavioral levels. Its genetic tractability, transparency, connectome, and accessibility for in vivo cellular and molecular analyses are a few of the characteristics that make the organism such a powerful system for investigating mechanisms of learning and memory. It is able to learn and remember across many sensory modalities, including mechanosensation, chemosensation, thermosensation, oxygen sensing, and carbon dioxide sensing. C. elegans habituates to mechanosensory stimuli, and shows short-, intermediate-, and long-term memory, and context conditioning for mechanosensory habituation. The organism also displays chemotaxis to various chemicals, such as diacetyl and sodium chloride. This behavior is associated with several forms of learning, including state-dependent learning, classical conditioning, and aversive learning. C. elegans also shows thermotactic learning in which it learns to associate a particular temperature with the presence or absence of food. In addition, both oxygen preference and carbon dioxide avoidance in C. elegans can be altered by experience, indicating that they have memory for the oxygen or carbon dioxide environment they were reared in. Many of the genes found to underlie learning and memory in C. elegans are homologous to genes involved in learning and memory in mammals; two examples are crh-1, which is the C. elegans homolog of the cAMP response element-binding protein (CREB), and glr-1, which encodes an AMPA glutamate receptor subunit. Both of these genes are involved in long-term memory for tap habituation, context conditioning in tap habituation, and chemosensory classical conditioning. C. elegans offers the advantage of having a very small nervous system (302 neurons), thus it is possible to understand what these conserved genes are doing at the level of single identified neurons. As many mechanisms of learning and memory in C. elegans appear to be similar in more complex organisms including humans, research with C. elegans aids our ever-growing understanding of the fundamental mechanisms of learning and memory across the animal kingdom.

Article

Douglas K. Reilly and Jagan Srinivasan

To survive, animals must properly sense their surrounding environment. The types of sensation that allow for detecting these changes can be categorized as tactile, thermal, aural, or olfactory. Olfaction is one of the most primitive senses, involving the detection of environmental chemical cues. Organisms must sense and discriminate between abiotic and biogenic cues, necessitating a system that can react and respond to changes quickly. The nematode, Caenorhabditis elegans, offers a unique set of tools for studying the biology of olfactory sensation. The olfactory system in C. elegans is comprised of 14 pairs of amphid neurons in the head and two pairs of phasmid neurons in the tail. The male nervous system contains an additional 89 neurons, many of which are exposed to the environment and contribute to olfaction. The cues sensed by these olfactory neurons initiate a multitude of responses, ranging from developmental changes to behavioral responses. Environmental cues might initiate entry into or exit from a long-lived alternative larval developmental stage (dauer), or pheromonal stimuli may attract sexually mature mates, or repel conspecifics in crowded environments. C. elegans are also capable of sensing abiotic stimuli, exhibiting attraction and repulsion to diverse classes of chemicals. Unlike canonical mammalian olfactory neurons, C. elegans chemosensory neurons express more than one receptor per cell. This enables detection of hundreds of chemical structures and concentrations by a chemosensory nervous system with few cells. However, each neuron detects certain classes of olfactory cues, and, combined with their synaptic pathways, elicit similar responses (i.e., aversive behaviors). The functional architecture of this chemosensory system is capable of supporting the development and behavior of nematodes in a manner efficient enough to allow for the genus to have a cosmopolitan distribution.

Article

Kevin T. Larkin, Alaina G. Tiani, and Leah A. Brown

Based on its distinctive innervation between the brain and body, the vagal nerve has long been considered to play an important role in explaining how exposure to stress leads to numerous psychiatric disorders and cardiac diseases. In contrast to activation of the sympathetic nervous system during exposures to stress, the vagal nerve is responsible for parasympathetic regulation of visceral activity including cardiac functioning that often but not always co-occurs during periods of stress. Although methods exist to measure vagal nerve influences on the heart directly, most of the literature on both human and animal participants’ responses to stress employs the measurement of heart rate variability (HRV). HRV, the tendency for the heart rate to increase and decrease in adaptation to the changing physiological and external environment, can be easily detected using surface electrodes; several HRV parameters have been shown to be valid indicators of parasympathetic nerve activity. Theories of the evolutionary heritage of the vagal nerve, like Porges’ polyvagal theory and the subsequent neurovisceral integration perspective of Thayer and colleagues that traces the autonomic regulation of the heart into higher cortical regions, have served as important conceptual works to guide empirical work examining the effects of stress on both tonic and phasic vagal activity. A number of methodological approaches have been employed to evaluate whether exposure to stress affects vagal tone, including use of animal models, case-control samples of humans exposed to stressful living situations, and samples of humans diagnosed with a range of psychiatric disorders. Findings from studies comprising this literature support a relation between exposure to stress and reduced cardiac vagal tone. Both humans and animals typically exhibit reductions in daily HRV when exposed to a range of stressful situations or contexts. The relation between stress and phasic alterations in vagal functioning, the magnitude of the acute change in HRV in response to an acute stressor, is more complicated, likely involving significant moderating variables that have yet to be elucidated. In sum, considerable evidence supports an important neuroregulatory role of the vagal nerve in modulating the body’s response to environmental stress and potentially serving as an avenue for understanding how exposure to stress increases risk for psychiatric disorders as well as cardiovascular disease.

Article

Josef P. Rauschecker

When one talks about hearing, some may first imagine the auricle (or external ear), which is the only visible part of the auditory system in humans and other mammals. Its shape and size vary among people, but it does not tell us much about a person’s abilities to hear (except perhaps their ability to localize sounds in space, where the shape of the auricle plays a certain role). Most of what is used for hearing is inside the head, particularly in the brain. The inner ear transforms mechanical vibrations into electrical signals; then the auditory nerve sends these signals into the brainstem, where intricate preprocessing occurs. Although auditory brainstem mechanisms are an important part of central auditory processing, it is the processing taking place in the cerebral cortex (with the thalamus as the mediator), which enables auditory perception and cognition. Human speech and the appreciation of music can hardly be imagined without a complex cortical network of specialized regions, each contributing different aspects of auditory cognitive abilities. During the evolution of these abilities in higher vertebrates, especially birds and mammals, the cortex played a crucial role, so a great deal of what is referred to as central auditory processing happens there. Whether it is the recognition of one’s mother’s voice, listening to Pavarotti singing or Yo-Yo Ma playing the cello, hearing or reading Shakespeare’s sonnets, it will evoke electrical vibrations in the auditory cortex, but it does not end there. Large parts of frontal and parietal cortex receive auditory signals originating in auditory cortex, forming processing streams for auditory object recognition and auditory-motor control, before being channeled into other parts of the brain for comprehension and enjoyment.

Article

In response to changes in metabolic demand, the cardiovascular and respiratory systems are regulated in a highly coordinated fashion, such that both ventilation and cardiac output increase in a parallel fashion, thus maintaining a relatively constant level of arterial blood PO2, PCO2, and pH. In addition, external alerting stimuli that trigger defensive or orienting behavioral responses also trigger coordinated cardiorespiratory changes that are appropriate for the particular behavior. Furthermore, environmental challenges such as hypoxia or submersion evoke complex cardiovascular and respiratory response that have the effect of increasing oxygen uptake and/or conserving the available oxygen. The brain mechanisms that are responsible for generating coordinated cardiorespiratory responses can be divided into reflex mechanisms and feedforward (central command) mechanisms. Reflexes that regulate cardiorespiratory function arise from a wide variety of internal receptors, and include those that signal changes in blood pressure, the level of blood oxygenation, respiratory activity, and metabolic activity. In most cases more than one reflex is activated, so that the ultimate cardiorespiratory response depends upon the interaction between different reflexes. The essential central pathways that subserve these reflexes are largely located within the brainstem and spinal cord, although they can be powerfully modulated by descending inputs arising from higher levels of the brain. The brain defense mechanisms that regulate the cardiorespiratory responses to external threatening stimuli (e.g., the sight, sound, or odor of a predator) are highly complex, and include both subcortical and cortical systems. The subcortical system, which includes the basal ganglia and midbrain colliculi as essential components, is phylogenetically ancient and generates immediate coordinated cardiorespiratory and motor responses to external stimuli. In contrast, the defense system that includes the cortex, hypothalamus, and limbic system evolved at a later time, and is better adapted to generating coordinated responses to external stimuli that involve cognitive appraisal.

Article

Simona Candiani and Mario Pestarino

The central and peripheral nervous systems of amphioxus adults and larvae are characterized by morphofunctional features relevant to understanding the origins and evolutionary history of the vertebrate CNS. Classical neuroanatomical studies are mainly on adult amphioxus, but there has been a recent focus, both by TEM and molecular methods, on the larval CNS. The latter is small and remarkably simple, and new data on the localization of glutamatergic, GABAergic/glycinergic, cholinergic, dopaminergic, and serotonergic neurons within the larval CNS are now available. In consequence, it has been possible begin the process of identifying specific neuronal circuits, including those involved in controlling larval locomotion. This is especially useful for the insights it provides into the organization of comparable circuits in the midbrain and hindbrain of vertebrates. A much better understanding of basic chordate CNS organization will eventually be possible when further experimental data will emerge.

Article

Z. Yan Wang and Clifton W. Ragsdale

Over 700 species of cephalopods live in the Earth’s waters, occupying almost every marine zone, from the benthic deep to the open ocean to tidal waters. The greatly varied forms and charismatic behaviors of these animals have long fascinated humans. Cephalopods are short-lived, highly mobile predators with sophisticated brains that are the largest among the invertebrates. While cephalopod brains share a similar anatomical organization, the nervous systems of coleoids (octopus, squid, cuttlefish) and nautiloids all display important lineage-specific neural adaptations. The octopus brain, for example, has for its arms a well-developed tactile learning and memory system that is vestigial in, or absent from, that of other cephalopods. The unique anatomy of the squid giant fiber system enables rapid escape in the event of capture. The brain of the nautilus comprises fewer lobes than its coleoid counterparts, but contains olfactory system structures and circuits not yet identified in other cephalopods.

Article

Anna Di Cosmo and Gianluca Polese

Within the Phylum Mollusca, cephalopods encompass a small and complex group of exclusively marine animals that live in all the oceans of the world with the exception of the Black and Caspian seas. They are distributed from shallow waters down into the deep sea, occupying a wide range of ecological niches. They are dominant predators and themselves prey with high visual capability and well-developed vestibular, auditory, and tactile systems. Nevertheless, their perceptions are chemically facilitated, so that water-soluble and volatile odorants are the key mediators of many physiological and behavioral events. For cephalopods as well as the other aquatic animals, chemical cues convey a remarkable amount of information critical to social interaction, habitat selection, defense, prey localization, courtship and mating, affecting not only individual behavior and population-level processes, but also community organization and ecosystem function. Cephalopods possess chemosensory systems that have anatomical similarities to the olfactory systems of land-based animals, but the molecules perceived from distance are different because their water solubility is of importance. Many insoluble molecules that are detected from distance on land must, in an aquatic system, be perceived by direct contact with the odour source. Most of the studies regarding olfaction in cephalopods have been performed considering only waterborne molecules detected by the “olfactory organs.” However cephalopods are also equipped with “gustatory systems” consisting of receptors distributed on the arm suckers in octopods, buccal lips in decapods, and tentacles in nautiluses. To date, what is known about the olfactory organ in cephalopods comes from studies on nautiloids and coleoids (decapods and octopods). In the nautiloid’s olfactory system, there is a pair of rhinophores located below each eye and open to the environment with a tiny pore, whereas in coleoids a small pit of ciliated cells is present on either side of the head below the eyes close to the mantle edge.

Article

Hiroshi Ueda

Chemoreception is the physiological capacity whereby organisms detect the varied external and internal chemical information required for survival and is the most primitive sensory process. Fish living in water have respiratory, gustatory, and olfactory chemosensory systems that detect water-soluble chemical cues. Respiratory chemoreception mainly in the gills detects changes in the levels of three respiratory gases: oxygen (O2), carbon dioxide (CO2), and ammonia (NH3). Gustatory chemoreception (gustation), which involves several taste receptor genes, is primarily involved in the tasting of foods. Olfactory chemoreception (olfaction), which involves between 15 and 150 olfactory receptor genes, is involved in a variety of important biological functions such as procuring foods, recognizing hazards (predators, contaminants, and toxic and alarm substances), discriminating species (individual, kin, and conspecific), controlling social behavior (dominance hierarchies, symbiotic behavior, territorial behavior, and schooling behavior), and reproductive and migratory behavior (mating, search for spawning site, imprinting, and homing). The olfactory functions are primarily controlled by hormones secreted from various endocrine glands that are the key mediators and integrators of external and internal information in organisms. Conversely, olfactory stimuli cause changes in hormone conditions. One good example is the amazing olfactory abilities of salmon. They can memorize information related to their natal stream odors during downstream migration in juveniles so that, after they travel thousands of kilometers in the ocean over many years during feeding migration, they are able to use their homing abilities to migrate precisely to their natal stream for reproduction in adults. Olfactory memory formation and retrieval of natal stream odors in salmon, which are primarily controlled by the brain–pituitary–thyroid hormones and brain–pituitary–gonad hormones, respectively, are essential to imprinting and homing migration. Salmon olfactory systems can discriminate seasonally and yearly stable compositions of dissolved amino acids in their natal streams produced by biofilms in the riverbed. Ocean and freshwater ecosystems may have been affected by climate change-related CO2-induced acidification that impairs olfactory-mediated neural and behavioral responses in fish.

Article

Megan A.K. Peters

The human brain processes noisy information to help make adaptive choices under uncertainty. Accompanying these decisions about incoming evidence is a sense of confidence: a feeling about whether a decision is correct. Confidence typically covaries with the accuracy of decisions, in that higher confidence is associated with higher decisional accuracy. In the laboratory, decision confidence is typically measured by asking participants to make judgments about stimuli or information (type 1 judgments) and then to rate their confidence on a rating scale or by engaging in wagering (type 2 judgments). The correspondence between confidence and accuracy can be quantified in a number of ways, some based on probability theory and signal detection theory. But decision confidence does not always reflect only the probability that a decision is correct; confidence can also reflect many other factors, including other estimates of noise, evidence magnitude, nearby decisions, decision time, and motor movements. Confidence is thought to be computed by a number of brain regions, most notably areas in the prefrontal cortex. And, once computed, confidence can be used to drive other behaviors, such as learning rates or social interaction.

Article

Yaniv Cohen, Emmanuelle Courtiol, Regina M. Sullivan, and Donald A. Wilson

Odorants, inhaled through the nose or exhaled from the mouth through the nose, bind to receptors on olfactory sensory neurons. Olfactory sensory neurons project in a highly stereotyped fashion into the forebrain to a structure called the olfactory bulb, where odorant-specific spatial patterns of neural activity are evoked. These patterns appear to reflect the molecular features of the inhaled stimulus. The olfactory bulb, in turn, projects to the olfactory cortex, which is composed of multiple sub-units including the anterior olfactory nucleus, the olfactory tubercle, the cortical nucleus of the amygdala, the anterior and posterior piriform cortex, and the lateral entorhinal cortex. Due to differences in olfactory bulb inputs, local circuitry and other factors, each of these cortical sub-regions appears to contribute to different aspects of the overall odor percept. For example, there appears to be some spatial organization of olfactory bulb inputs to the cortical nucleus of the amygdala, and this region may be involved in the expression of innate odor hedonic preferences. In contrast, the olfactory bulb projection to the piriform cortex is highly distributed and not spatially organized, allowing the piriform to function as a combinatorial, associative array, producing the emergence of experience-dependent odor-objects (e.g., strawberry) from the molecular features extracted in the periphery. Thus, the full perceptual experience of an odor requires involvement of a large, highly dynamic cortical network.

Article

Donald Edwards

Crayfish are decapod crustaceans that use different forms of escape to flee from different types of predatory attacks. Lateral and Medial Giant escapes are released by giant interneurons of the same name in response to sudden, sharp attacks from the rear and front of the animal, respectively. A Lateral Giant (LG) escape uses a fast rostral abdominal flexion to pitch the animal up and forward at very short latency. It is succeeded by guided swimming movements powered by a series of rapid abdominal flexions and extensions. A Medial Giant (MG) escape uses a fast, full abdominal flexion to thrust the animal directly backward, and is also followed by swimming that moves the animal rapidly away from the attacker. More slowly developing attacks evoke Non-Giant (NG) escapes, which have a longer latency, are varied in the form of abdominal flexion, and are directed initially away from the attacker. They, too, are followed by swimming away from the attacker. The neural circuitry for LG escape has been extensively studied and has provided insights into the neural control of behavior, synaptic integration, coincidence detection, electrical synapses, behavioral and synaptic plasticity, neuroeconomical decision-making, and the modulatory effects of monoamines and of changes in the animal’s social status.

Article

Charles Derby and Manfred Schmidt

Olfaction is a chemical sense present not only in mammals, insects, and other terrestrial animals, but also in crustaceans, most of which are aquatic. Crustaceans use olfaction for detecting and responding in appropriate ways to chemicals relevant to most ecological contexts, including: environmental cues indicating quality of food, habitat, and location; interspecies cues indicating presence of predators and competitors; and intraspecific signals indicating social status of conspecifics and presence of possible mating partners. Olfaction is only one of the chemical senses of crustaceans, being distinguished based on anatomical and functional features of the sensory neurons detecting the chemicals and the pathways within the central nervous system that processes this information.

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

Tim C. Kietzmann, Patrick McClure, and Nikolaus Kriegeskorte

The goal of computational neuroscience is to find mechanistic explanations of how the nervous system processes information to give rise to cognitive function and behavior. At the heart of the field are its models, that is, mathematical and computational descriptions of the system being studied, which map sensory stimuli to neural responses and/or neural to behavioral responses. These models range from simple to complex. Recently, deep neural networks (DNNs) have come to dominate several domains of artificial intelligence (AI). As the term “neural network” suggests, these models are inspired by biological brains. However, current DNNs neglect many details of biological neural networks. These simplifications contribute to their computational efficiency, enabling them to perform complex feats of intelligence, ranging from perceptual (e.g., visual object and auditory speech recognition) to cognitive tasks (e.g., machine translation), and on to motor control (e.g., playing computer games or controlling a robot arm). In addition to their ability to model complex intelligent behaviors, DNNs excel at predicting neural responses to novel sensory stimuli with accuracies well beyond any other currently available model type. DNNs can have millions of parameters, which are required to capture the domain knowledge needed for successful task performance. Contrary to the intuition that this renders them into impenetrable black boxes, the computational properties of the network units are the result of four directly manipulable elements: input statistics, network structure, functional objective, and learning algorithm. With full access to the activity and connectivity of all units, advanced visualization techniques, and analytic tools to map network representations to neural data, DNNs represent a powerful framework for building task-performing models and will drive substantial insights in computational neuroscience.

Article

The majority of anxiety disorders emerge during childhood and adolescence, a developmental period characterized by dynamic changes in frontolimbic circuitry. Frontolimbic circuitry plays a key role in fear learning and has been a focus of recent efforts to understand the neurobiological correlates of anxiety disorders across development. Although less is known about the neurobiological underpinnings of anxiety disorders in youth than in adults, studies of pediatric anxiety have revealed alterations in both the structure and function of frontolimbic circuitry. The amygdala, prefrontal cortex (PFC), anterior cingulate cortex (ACC), and hippocampus contribute to fear conditioning and extinction, and interactions between these regions have been implicated in anxiety during development. Specifically, children and adolescents with anxiety disorders show altered amygdala volumes and exhibit heightened amygdala activation in response to neutral and fearful stimuli, with the magnitude of signal change in amygdala reactivity corresponding to the severity of symptomatology. Abnormalities in the PFC and ACC and their connections with the amygdala may reflect weakened top-down control or compensatory efforts to regulate heightened amygdala reactivity associated with anxiety. Taken together, alterations in frontolimbic connectivity are likely to play a central role in the etiology and maintenance of anxiety disorders. Future studies should aim to translate the emerging understanding of the neurobiological bases of pediatric anxiety disorders to optimize clinical interventions for youth.

Article

Talita de Melo e Silva, Catherine Miriam Czeisler, and José Javier Otero

Breathing is essential for survival and is precisely regulated by the nervous system. From a neuroanatomical perspective, the respiratory tract is innervated by afferent and efferent autonomic nerves, which regulate aspects of airway function and ensure appropriate tissue oxygenation. The general concepts of how the peripheral nervous system (PNS) develops as it relates to lung function are reviewed. The vagus (cranial nerve X), a mixed motor and sensory nerve, supplies parasympathetic and sensory fibers to the airways. During development, preganglionic visceromotor efferent neurons of the cranial nerves arise in the hindbrain basal plate and later migrate dorsally through the neuroepithelium. The neural crest is a migratory and multipotent embryonic cell population that develops at the dorsal portion of the neural tube, which delaminates from the neuroepithelium to enter distinct pathways, forming various derivatives, among which include the peripheral nervous system. Neural crest cells emerging from the vagal region migrate into the ventral foregut and give rise to intrinsic ganglia in the respiratory tract that are innervated from the vagus and send out postganglionic fibers. The lung is innervated by sympathetic nerves derived from the upper thoracic and cervical ganglia. The sympathetic preganglionic neurons are derived from trunk neural crest cells that migrate, forming two chains of sympathetic ganglia referred to as the lateral vertebral sympathetic chains. Neural crest cells that migrate along defined pathways to generate sympathetic ganglia also derivate the dorsal root ganglia that send somatosensory afferent innervations to the respiratory tract.

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

Carlos A. Díaz-Balzac and José E. García-Arrarás

The nervous system of echinoderms has been studied for well over a century. Nonetheless, the information available is disparate, with in-depth descriptions for the nervous component of some groups or of particular organs while scant data is available for others. The best studied representatives to date are the nervous system of echinoid embryos and larva, and the adult holothurian nervous system. Although described sometimes inaccurately as a neural net, the echinoderm nervous system consists of well-defined neural structures. This is observed since early embryogenesis when activation of the anterior neuroectoderm gene regulatory networks initiate the formation of the embryonic nervous system. This system then undergoes expansion and differentiation to form the larval nervous system, which is centered on the ciliary bands. This “simpler” nervous system is then metamorphosed into the adult echinoderm nervous system. The adult echinoderm nervous system is composed of a central nervous system made up of a nerve ring connected to a series of radial nerve cords. Peripheral nerves extending from the radial nerve cords or nerve ring connect with the peripheral nervous system, located in other organs or effectors including the viscera, podia, body wall muscles, and connective tissue. Both the central and peripheral nervous systems are composed of complex and diverse subdivisions. These are mainly characterized by the expression of neurotransmitters, namely acetylcholine, catecholamines, histamine, amino acids, GABA, and neuropeptides. Other areas of interest include the amazing regenerative capabilities of echinoderms that have been shown to be able to regenerate their nervous system components; and the analysis of the echinoderm genome that has provided essential insights into the molecular basis of how echinoderms develop an adult pentaradial symmetry from bilaterally symmetric larvae and the role of the nervous system in this process.

Article

Although the Cnidaria have evolved a wide range of body forms matched with an equally varied neural anatomy, individual species exhibit common patterns of behavior. For example, in all species a key challenge for the nervous system is to transfer food from the peripherally mounted tentacles to the centrally located stomach. Foraging movements, necessary to maintain the food supply, must be accomplished in such a way as to avoid interference with the primary objective of getting prey into the mouth. Furthermore, the hunt for prey must be balanced by a measured response to “threat.” Different species respond to threat in markedly different ways, but in each case foraging is inhibited, just as it is during transmission of food. One hundred years ago, G. H. Parker questioned whether a centralized or a locally organized nervous system could best account for sea anemone behavior. Anatomical and electrophysiological studies now suggest that in most Cnidaria there is a degree of hierarchical control, with local reflexes coordinated by more condensed systems of neurons. This organization is highly developed in the nerve rings of hydrozoan medusae and takes the form of ganglion-like rhopalia in the Cubozoa. Even in hydrozoan polyps such as Hydra there are at least four separate neuronal systems. It is likely that the underlying mechanisms (containing both homologous and analogous elements) will be best revealed by a comparative approach that directly relates behavior with its molecular basis. Useful examples include comparisons between sea anemones with and without through-conducting systems; between hydra with and without oral rings; between medusae with and without coordinated escape swimming. Recent advances in transgenomic labeling have shown the way forward.