Multisensory integration (MSI) combines information from more than one sensory modality to elicit behaviours distinct from unisensory behaviours. MSI is best understood in animals with complex brains and specialized centres for parsing different modes of sensory information, but dispersive larvae of sessile marine invertebrates utilize multimodal environmental sensory stimuli to base irreversible settlement decisions on, and most lack complex brains. Here, we examined the sensory determinants of settlement in actinula larvae of the hydrozoan Ectopleura crocea (Cnidaria), which possess a diffuse nerve net. A factorial settlement study revealed that photo-, chemo- and mechanosensory cues each influenced the settlement response in a complex and hierarchical manner that was dependent on specific combinations of cues, an indication of MSI. Additionally, sensory gene expression over development peaked with developmental competence to settle, which in actinulae, requires cnidocyte discharge. Transcriptome analyses also highlighted several deep homological links between cnidarian and bilaterian mechano-, chemo-, and photosensory pathways. Fluorescent in situ hybridization studies of candidate transcripts suggested cellular partitioning of sensory function among the few cell types that comprise the actinula nervous system, where ubiquitous polymodal sensory neurons expressing putative chemo- and photosensitivity interface with mechanoreceptive cnidocytes. We propose a simple multisensory processing circuit, involving polymodal chemo/photosensory neurons and mechanoreceptive cnidocytes, that is sufficient to explain MSI in actinulae settlement. Our study demonstrates that MSI is not exclusive to complex brains, but likely predated and contextualized their evolution.
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After a period marked by one-sided emphasis on psychodynamics and social issues, or what could be called "brainless" psychiatry on account of its relative neglect of cerebral processes, we are witnessing an opposite trend towards extreme biologism or "mindless" psychiatry. The pendulum has swung periodically from one to the other of these reductionistic positions throughout the history of psychiatry. The author argues that neither brainless nor mindless psychiatry can do justice to the complexity of mental illness and to the treatment of patients. Psychiatry's distinguishing feature as a clinical discipline is its equal concern with subjective experience, or the mind, and with the body, including brain function, which together constitute a person, a psychiatrist's proper focus of inquiry and intervention. Moreover, a person, viewed as a mindbody complex, is in constant interaction with the environment. It follows that both study of mental illness and clinical practice need to take into account the psychological, the biological and the social aspects. These three aspects are not mutually reducible and are indispensable for the understanding and treatment of the individual patient. Such a comprehensive, biopsychosocial approach provides an antithesis to the reductionistic viewpoints and, in the writer's opinion, is both practically and theoretically most satisfying.
For highly heritable brain disorders, such as schizophrenia and autism, investigating genetic effects on the level of neural systems seems an obvious approach. Nevertheless, the usefulness of the intermediate phenotypes ('endo' phenotypes) continues to be debated energetically. We argue that, while not all intermediate phenotypes are created equal, the hypothesis-driven investigation of the translational cascades linking genetic variation to disturbed behavior is a viable and important strategy that should not be supplanted by an exclusive focus on brainless, clinical/categorical phenotypes investigated in very large numbers of participants.
In this study, we discovered a phenomenon in which a quadruped robot without any sensors or microprocessor can autonomously generate the various gait patterns of animals using actuator characteristics and select the gaits according to the speed. The robot has one DC motor on each limb and a slider-crank mechanism connected to the motor shaft. Since each motor is directly connected to a power supply, the robot only moves its foot on an elliptical trajectory under a constant voltage. Although this robot does not have any computational equipment such as sensors or microprocessors, when we applied a voltage to the motor, each limb begins to adjust its gait autonomously and finally converged to a steady gait pattern. Furthermore, by raising the input voltage from the power supply, the gait changed from a pace to a half-bound, according to the speed, and also we observed various gait patterns, such as a bound or a rotary gallop. We investigated the convergence property of the gaits for several initial states and input voltages and have described detailed experimental results of each gait observed.
A review of the behavioral and neurophysiological estimates of the time-course of compound word recognition brings to light a paradox whereby temporal activity associated with lexical variables in behavioral studies predates temporal activity of seemingly comparable lexical processing in neuroimaging studies. However, under the assumption that brain activity is a cause of behavior, the earliest reliable behavioral effect of a lexical variable must represent an upper temporal bound for the origin of that effect in the neural record. The present research provides these behavioral bounds for lexical variables involved in compound word processing. We report data from five naturalistic reading studies in which participants read sentences containing English compound words, and apply a distributional technique of survival analysis to resulting eye-movement fixation durations (Reingold & Sheridan, 2014). The results of the survival analysis of the eye-movement record place a majority of the earliest discernible onsets of orthographic, morphological, and semantic effects at less than 200 ms (with a range of 138-269 ms). Our results place constraints on the absolute time-course of effects reported in the neurolinguistic literature, and support theories of complex word recognition which posit early simultaneous access of form and meaning.
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Because of its peculiar biology and the ease with which it can be cultured, the acellular slime mould Physarum polycephalum has long been a model organism in a range of disciplines. Due to its macroscopic, syncytial nature, it is no surprise that it has been a favourite amongst cell biologists. Its inclusion in the experimental tool kit of behavioural ecologists is much more recent. These recent studies have certainly paid off. They have shown that, for an organism that lacks a brain or central nervous system, P. polycephalum shows rather complex behaviour. For example, it is capable of finding the shortest path through a maze, it can construct networks as efficient as those designed by humans, it can solve computationally difficult puzzles, it makes multi-objective foraging decisions, it balances its nutrient intake and it even behaves irrationally. Are the slime mould's achievements simply "cute", worthy of mentioning in passing but nothing to take too seriously? Or do they hint at the fundamental processes underlying all decision making? We will address this question after reviewing the decision-making abilities of the slime mould.
In many animals in which females store sperm, males may detect female mating status and, in order to outcompete rival sperm, increase ejaculate size when copulating with non-virgin females. Although most studies have been restricted to organisms with separate sexes, theoretical models suggest that sperm competition should also be an important selective agent shaping life-history traits in simultaneous hermaphrodites. Nevertheless, the empirical support for ejaculate adjustment in a mating opportunity is scarce in hermaphrodites. In the present study, we performed a double-mating experiment to determine whether earthworms (Eisenia andrei) detect the mating status of their partners and whether they respond by adjusting their ejaculate. We found that earthworms triplicated the donated sperm when mating with a non-virgin mate. Moreover, such increases were greater when the worms were mated with larger (more fecund) partners, indicating that earthworms perform a fine-tune control of ejaculate volume. The results of the present study suggest that, under high intensity of sperm competition, partner evaluation is subject to intense selection in hermaphrodite animals, and donors are selective about to whom they donate how much sperm.
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Brittle stars move with remarkable whole-body coordination despite lacking a central brain. With five identical arms radiating from a central disc, they predominantly adopt a bilaterally symmetrical rowing gait: one arm leads, two neighbouring arms row in synchrony and the remaining arms trail. This raises a puzzle: how does a brainless nervous system generate coherent whole-body gaits, and why does it favour rowing? To address this, this work introduces an in silico framework combining (i) a three-dimensional model of brittle star morphology in a physics simulator, (ii) an artificial neural network (ANN) architecture that mirrors the decentralized arm-level ganglia, which interconnect through the nerve ring and (iii) reinforcement learning (RL) to optimize controllers for locomotion. Analysis of optimized controllers shows that ganglia behave as distributed oscillators whose coupling via the nerve ring yields synchronization, analogous to that of central pattern generators (CPGs). Gait analysis reveals that rowing emerges as the strategy most compatible with the arms' dual role as effectors and sensors. Taken together, these results provide a mechanistic view of how decentralized neural dynamics and sensory constraints shape brittle star locomotion. The presented framework offers an open-ended test bed for hypotheses inaccessible in vivo, and more broadly, for exploring decentralized control in embodied agents. We provide a link to our project web page and interactive results dashboard: https://airo.ugent.be/projects/brittle-star.
Memory is generally thought to be stored within centralized neural circuits. However, whether learned behaviors can persist in the absence of a brain remains unresolved. Planaria (Girardia spp.) possess a primitive cephalic ganglion and a remarkable capacity for regeneration, providing a unique system to examine non-cephalic memory retention. The primary aim of this study was to determine whether sucrose-induced conditioned place preference (CPP) is retained in posterior, brainless planarian fragments. Planaria were trained using a Pavlovian conditioning paradigm in which an initially unpreferred surface was paired with a 10% sucrose solution, resulting in a robust shift in surface preference. Following amputation, anterior fragments containing the cephalic ganglion as well as posterior fragments lacking the brain preserved the conditioned preference, demonstrating that reward-associated memory is stored even outside the cephalic nervous system. As a secondary objective, we examined the role of dopaminergic reinforcement using a D1 dopamine receptor antagonist during training. While antagonist-treated planaria failed to develop a CPP, posterior fragments from these amputated planaria likewise showed no conditioned preference, indicating that dopamine-dependent signaling is essential for sucrose-associated memory formation across the body. These results provide support for the hypothesis that reward-associated memory in planaria is distributed beyond the brain and can be modulated by dopaminergic pathways, highlighting the utility of this model for exploring fundamental mechanisms of reward, memory, and potential pharmacological interventions.
Sea stars use hundreds of tube feet on their oral surface to crawl, climb, and navigate complex environments, despite lacking a central brain. While tube foot morphology and function as muscular hydrostats are well described, the mechanisms that coordinate their collective dynamics remain poorly understood. To investigate these dynamics, we employed an optical imaging method based on frustrated total internal reflection (FTIR) to visualize and quantify tube foot adhesive contacts in real time in the species Asterias rubens across individuals spanning a wide size range. Our results reveal an inverse relationship between crawling speed and tube foot adhesion time, indicating that sea stars regulate locomotion by modulating contact duration in response to mechanical load. To test this, we conducted perturbation experiments using 3D-printed backpacks that increased body mass by 25 and 50%, along with biomechanical modeling of decentralized feedback control of the tube feet. The added load significantly increased adhesion time, supporting the role of a load-dependent mechanical adaptation. We further investigated inverted locomotion, both experimentally and through simulation, and found that tube feet adjust their contact behavior when the animal is oriented upside down relative to gravity. Together, these findings demonstrate that sea stars adapt their locomotion to changing mechanical demands by modulating tube foot-substrate interactions, revealing a robust decentralized control strategy in a brainless organism and highlighting general principles of distributed control in biology and soft robotics.
Multicellular organisms utilize epithelial folding to achieve remarkable three-dimensional forms. During embryonic development, stereotypical epithelial folds emerge from underlying active cellular and molecular processes including cell shape change and differential cell growth. However, the origin of epithelial folding in early animals and how folding may be harnessed in synthetic systems remain open questions. Here, we identify a modality of behavior-induced epithelial folding and unfolding arising from cilia-substrate adhesion and ciliary walking in the basal animal Trichoplax adhaerens (phylum Placozoa). We show that T. adhaerens is capable of exhibiting dynamic nonstereotyped folding states, providing a 3D perspective to an organism previously only characterized in its 2D state. We correlate these folding states to local substrate geometry, revealing that the animal conforms to available substrate surface area, promoting the maintenance of a folded state. Using 4D fluorescence light sheet microscopy, we characterize fold geometry, curvature evolution during unfolding, and the nonstereotypy of unfolding behavior. Through repeated unfolding trials, we reveal the robustness and timescales associated with unfolding behavior and employ scaling analysis and toy model simulations to establish how collective ciliary activity can robustly drive unfolding. In this way, despite lacking any folding-unfolding "pathway," transitions between folding and unfolding states emerge as a function of the animal's environment and motility. Our work reveals a remarkable behavior exhibited by a brainless, nerveless animal, and demonstrates the capacity for 3D-2D transitions in folding epithelial sheets using ciliary activity.
This perspective article presents the work of Dr. Edmund (Ed) C Levin (1931-2022), child and adolescent psychiatrist in Berkeley, California. Levin drew from over half a century of continuity of clinical practice with his patients and knowledge of developmental psychopathology. He was witness to a paradigm shift in American psychiatry from what Eisenberg termed a 'brainless' to a 'mindless' approach in research and clinical practice. He was motivated by concern for medical ethical treatment guided by awareness of the patient's individual biopsychosocial contributing factors to their predicament and symptoms. He addressed the pediatric bipolar disorder era by championing a recognition of the long-term effects of childhood maltreatment and developmental trauma across the lifespan. His work in both child and youth residential and geriatric residential units exemplified this.
Sleep is a conserved physiological phenomenon across species. It is mainly controlled by two processes: a circadian clock that regulates the timing of sleep and a homeostat that regulates the sleep drive. Even cnidarians, such as Hydra and jellyfish, which lack a brain, display sleep-like states. However, the manner in which environmental cues affect sleep-like states in these organisms remains unknown. In the present study, we investigated the effects of light and temperature cycles on the sleep-like state in Hydra vulgaris. Our findings indicate that Hydra responds to temperature cycles with a difference of up to 5° C, resulting in decreased sleep duration under light conditions and increased sleep duration in dark conditions. Furthermore, our results reveal that Hydra prioritizes temperature changes over light as an environmental cue. Additionally, our body resection experiments show tissue-specific responsiveness in the generation ofthe sleep-like state under different environmental cues. Specifically, the upper body can generate the sleep-like state in response to a single environmental cue. In contrast, the lower body did not respond to 12-h light-dark cycles at a constant temperature. These findings indicate that both light and temperature influence the regulation of the sleep-like state in Hydra. Moreover, these observations highlight the existence of distinct regulatory mechanisms that govern patterns of the sleep-like state in brainless organisms, suggesting the potential involvement of specific regions for responsiveness of environmental cues for regulation of the sleep-like state.
Active systems of self-propelled agents, e.g., birds, fish, and bacteria, can organize their collective motion into myriad autonomous behaviors. Ubiquitous in nature and across length scales, such phenomena are also amenable to artificial settings, e.g., where brainless self-propelled robots orchestrate their movements into spatial-temporal patterns via the application of external cues or when confined within flexible boundaries. Like their natural counterparts, these approaches typically require many units to initiate collective motion, so controlling the ensuing dynamics is challenging. Here, we demonstrate a simple mechanism that leverages nonlinear elasticity to tame near-diffusive motile particles in forming structures capable of directed motion and other emergent behaviors. Our elasto-active system comprises two centimeter-sized self-propelled microbots connected with elastic beams. These microbots exert forces that suffice to buckle the beam and set the structure in motion. We first rationalize the physics of the interaction between the beam and the microbots. Then we use reduced-order models to predict the interactions of our elasto-active structures with boundaries, e.g., walls and constrictions, and demonstrate how they can exhibit remarkable emergent behaviors such as maze navigation. These findings demonstrate that allowing and understanding changes in body morphology can enhance the capabilities of active matter systems and enable the design of robotic materials capable of space exploration, adaptation, and complex interactions with their surrounding environment.