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Cephalopod Nervous System Organization  

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

Behavioral Neuroendocrinology: Cognition  

Victoria Luine

The demonstration of steroid binding proteins in brain areas outside of the hypothalamus was a key neuroendocrine discovery in the 1980s. These findings suggested that gonadal hormones, estradiol and testosterone, may have additional functions besides controlling reproduction through the hypothalamic–pituitary–gonadal axis (HPG) and that glucocorticoids may also influence neural functions not related to the hypothalamic–pituitary–adrenal axis (HPA). In the past 30 years, since the early 1990s, a body of neuroendocrine studies in animals has provided evidence for these hypotheses, and in 2020, it is generally accepted that steroid hormones exert robust influences over cognition—both learning and memory. Gonadal hormones, predominantly estrogens, enhance learning and memory in rodents and humans and influence cognitive processes throughout the lifespan. Gonadal hormones bind to classical nuclear estrogen receptors and to membrane receptors to influence cognition. In contrast to the generally positive effects of gonadal hormones on learning and memory, adrenal hormones (glucocorticoids in rodents or cortisol in primates) released during chronic stress have adverse effects on cognition, causing impairments in both learning and memory. However, emerging evidence suggests that impairments may be limited only to males, as chronic stress in females does not usually impair cognition and, in many cases, enhances it. The cognitive resilience of females to stress may result from interactions between the HPG and HPA axis, with estrogens exerting neuroprotective effects against glucocorticoids at both the morphological and neurochemical level. Overall, knowledge of the biological underpinnings of hormonal effects on cognitive function has enormous implications for human health and well-being by providing novel tools for mitigating memory loss, for treating stress-related disorders, and for understanding the bases for resilience versus susceptibility to stress.

Article

Caenorhabditis elegans Learning and Memory  

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

Crustacean Visual Circuits Underlying Behavior  

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

Psycholinguistic Research on Inflectional Morphology in the Romance Languages  

Claudia Marzi and Vito Pirrelli

Over the past decades, psycholinguistic aspects of word processing have made a considerable impact on views of language theory and language architecture. In the quest for the principles governing the ways human speakers perceive, store, access, and produce words, inflection issues have provided a challenging realm of scientific inquiry, and a battlefield for radically opposing views. It is somewhat ironic that some of the most influential cognitive models of inflection have long been based on evidence from an inflectionally impoverished language like English, where the notions of inflectional regularity, (de)composability, predictability, phonological complexity, and default productivity appear to be mutually implied. An analysis of more “complex” inflection systems such as those of Romance languages shows that this mutual implication is not a universal property of inflection, but a contingency of poorly contrastive, nearly isolating inflection systems. Far from presenting minor faults in a solid, theoretical edifice, Romance evidence appears to call into question the subdivision of labor between rules and exceptions, the on-line processing vs. long-term memory dichotomy, and the distinction between morphological processes and lexical representations. A dynamic, learning-based view of inflection is more compatible with this data, whereby morphological structure is an emergent property of the ways inflected forms are processed and stored, grounded in universal principles of lexical self-organization and their neuro-functional correlates.