搜索结果：Brain, behavior and evolution

Intranasal administration, as a non-invasive brain-targeted delivery strategy, offers a promising approach for the treatment of central nervous system disorders, particularly depression. Traditional oral or intravenous drug delivery is often limited by the restrictive permeability of the blood-brain barrier and the hepatic first-pass effect, which hinder effective drug accumulation in the brain. In contrast, the intranasal route leverages the olfactory and trigeminal neural pathways to enable direct drug transport from the nasal cavity to the brain, effectively bypassing the blood-brain barrier and significantly enhancing brain drug bioavailability. This article systematically reviews the research progress of intranasal drug delivery in the treatment of depression-like behaviors, highlighting the technological evolution of various drug-loading modalities, including solutions, gels, nanoparticles, in situ gels, and cell membrane biomimetic carriers, and analyzes their differences in nasal mucosal retention time, mucus penetration ability, and brain-targeting efficiency. Furthermore, it elaborates on the multiple antidepressant mechanisms of intranasal materials, such as regulating neurotransmitter systems (e.g., 5-Hydroxytryptamine, Dopamine, Glutamate), inhibiting neuroinflammation (e.g., microglial activation, inflammatory factor release), enhancing neuroplasticity (e.g., promoting hippocampal neurogenesis and synapse formation), and modulating the gut microbiota-gut-brain axis. Simultaneously, the article integrates data from multiple clinical trials, focusing on evaluating the efficacy and safety of intranasal formulations such as esketamine in treatment-resistant depression, highlighting their advantages of rapid onset and high response rates, and discussing management strategies for adverse reactions such as dose individualization, local irritation, and dissociative symptoms. Addressing current technical bottlenecks, such as uneven drug absorption due to nasal physiological differences, challenges in the large-scale production of nanocarriers, and insufficient long-term safety evidence, the article proposes that future research should focus on the development of intelligent responsive nanocarriers, the construction of multimodal synergistic treatment systems, the design of personalized medication regimens guided by precision medicine, and the coordinated advancement of real-world research and regulatory standards. This review aims to provide comprehensive theoretical support and development directions for the clinical translation of intranasal drug delivery in the field of depression treatment.

Brain lateralization has deep evolutionary roots in primates, and is often considered to reach its most pronounced expression in humans, particularly in relation to lateralized behaviors. However, little is known about the macroevolutionary dynamics of asymmetric endocranial shape across fossil and extant catarrhines. Here, we apply three-dimensional geometric morphometrics to a comparative sample of extant apes, humans, and fossil hominins to investigate patterns, rates, and directions of brain shape lateralization under an explicit phylogenetic framework. We analyzed 161 cranial endocasts representing 81 extant and extinct Catarrhine species, using high-resolution geometric morphometrics. We focus on endocast shape lateralization as an evolutionary component of endocranial morphology rather than on individual-level hemispheric differences. Rates of asymmetric shape change are quantified across lineages by using Phylogenetic Ridge Regression (RRphylo) to map evolutionary rates of endocast shape lateralization directly onto the cortical surface. Our results show that hominins exhibit distinctly higher rates of asymmetric endocranial shape evolution compared with nonhuman apes, with particularly pronounced changes observed along the lineage leading to modern humans. These changes are not explained by single-side brain size variation and are spatially concentrated in specific regions of the endocranial surface. The patterns we identified reflect macroevolutionary modifications of endocranial shape and do not constitute direct evidence of hemispheric functional specialization. Nevertheless, the observed evolutionary dynamics are consistent with broader scenarios involving increasing structural reorganization of the brain during hominin evolution. These findings provide a quantitative framework for investigating the evolutionary history of endocranial asymmetry and its potential biological correlates while maintaining a clear distinction between morphological evidence and functional interpretation.

Understanding the cognitive and biomechanical foundations of early hominin tool use represents a central focus in human evolutionary research. Although interdisciplinary work on early lithic technologies has explored each of these aspects separately, few experimental approaches have directly examined the interaction between neural and muscular systems during stone tool use. This study adopts a recently developed interdisciplinary approach to explore the impact of cumulative tool-related expertise (practical "know-how") on the dynamic brain-body interplay required for efficient early hominin stone tool use. Our experimental design compares Experts (with extensive practical knapping experience), Intermediates (with only theoretical knowledge), and Novices (with neither) performing two of the earliest known stone tool behaviors in the fossil record: hammerstone nut-cracking and Oldowan-style flake cutting. Using simultaneous electroencephalographic and electromyographic recordings, we analyzed neural activity in the left-frontal, premotor/motor, and left-parietal cortices alongside selective muscular activation in the hands and forearms. Our findings show that, during flake cutting, Experts display distinct beta-band neural activity in the left frontal and premotor/motor regions, and to a lesser extent in the left parietal region, accompanied by overall reduced muscular activation. In the nut-cracking task, Experts show reduced muscular effort and slightly elevated premotor/motor involvement, though to a much lesser degree. Importantly, Experts also present significant neural differences between the two tasks, suggesting task-specific cognitive strategies related to motor planning and coordination. In contrast, Novice participants demonstrate greater reliance on higher muscular effort and left-lateralized parietal regions, likely reflecting increased engagement of visuospatial processing and understanding tool function and mechanical knowledge. Altogether, these findings provide critical insights into the brain-hand interplay required for humanlike early stone tool use and highlight cumulative practical knowledge ("know-how") as a decisive factor of neuromechanical efficiency in early hominin technological behavior. They also encourage future experimental research on increased sample sizes to adopt integrated methods that jointly consider neural and muscular dynamics.

Research on the relationship between the evolution of ontogenetic locomotor milestones and the emergence of advanced cognition in early hominins is reviewed and discussed from an evo-devo perspective that incorporates theoretical underpinnings from the extended evolutionary synthesis. Comparative ontogenetic data from chimpanzee and human infants shed light on likely derivations in hominin locomotor milestones, their effect on the emergence of habitual bipedalism, and the latter's probable contribution(s) to cognitive evolution. Human babies' locomotor milestone of crawling on hands and knees is hypothesized to have been derived during hominin evolution in place of a knuckle-walking developmental stage that likely existed in the apelike predecessors of the earliest hominins. A review of comparative research suggests that evolutionary modifications in crawling, sitting, and pointing in addition to selection for bipedalism, contributed to the progressive evolution of both locomotion and advanced cognition in hominins. Comparisons of the ontogenetic development of locomotor stages in chimpanzee and human infants suggest that locomotor evolution and the emergence of advanced cognition were deeply intertwined during hominin evolution.

The brainstem connects the forebrain to the spinal cord. It consists of three layers, the ventral basis, the intermediate tegmentum, and the dorsal tectum. Caudo-rostrally, the brainstem is divided into the medulla oblongata or myelencephalon, the metencephalon, and the mesencephalon. The tegmentum is the most conserved part of the brainstem and contains the motor and sensory nuclei of cranial nerves (CN) III-XII. They are arranged in a mediolateral direction, and, unlike the spinal cord, their afferent and efferent fibers are not macroscopically separated. The tegmental reticular formation, the brainstem core, has a lattice structure with manifold longitudinal and transverse fibers and stacked neurons. Its architecture provides maximum convergence and divergence of intrinsic and ascending/descending information from the spinal cord and forebrain. It coordinates brainstem-based vital functions, and its integrity is essential for arousal, consciousness, and goal-directed behavior. Its small aminergic and cholinergic telencephalic projection nuclei have a profound impact on mood, motivation, and cognition. Human telencephalic evolution manifests in volume increases of the cerebral crura, pons, cerebellar hemispheres, olives, pyramidal tract, and medial lemniscus. However, the spatial constraints of the posterior fossa limited the proportional expansion of the brainstem during human telencephalic evolution, rendering this evolutionarily conserved structure increasingly vulnerable to malfunction and disease.

How the brains of domestic animals evolved under domestication remains poorly understood. We quantified brain shape variation in domestic dogs (n = 203, 111 breeds) and wolves (n = 40) using endocast-based 3D geometric morphometrics. Size, shape, and morphological integration were assessed on the whole brain, and in six morphofunctional subregions. Results demonstrate that domestication and artificial selection significantly restructured brain form and morphological integration patterns in dogs, reflecting mosaic evolution across brain subregions. Dogs exhibit a three-fold increase in brain shape variation relative to wolves, as well as expanded frontal lobes and areas putatively associated with social interaction behavior-these regions are also larger in cooperative vs. independent breeds. Morphological integration is higher in dogs than wolves, and in modern breeds compared to ancient breeds. Thus, rather than constrain, integration appears to facilitate neuroanatomical evolvability under domestication and breeding selection. Ancient dog breeds retain more wolf-like neuroanatomy. Breed function is a poor predictor of brain shape, but brain integration restructures according to breed function, with working breeds displaying the highest integration. These findings reveal the profound impact of domestication on neuroanatomical evolution, emphasizing neuroanatomical features linked to social behavior, and challenging prevailing assumptions about the role of structural integration on evolvability.

Background and Objectives: Brain metastases frequently evolve over time in multiple waves, especially in patients with prolonged survival. Despite repeated imaging and targeted therapies, lesion-level continuity is fragmented in clinical practice, as follow-up is typically limited to pairwise MRI comparisons. The aim of the study is to assess the ability of routine narrative MRI follow-up reports to preserve longitudinal lesion identity and to reconstruct a coherent trajectory of disease evolution. Materials and Methods: We conducted a single-center, retrospective, observational study of all brain MRI examinations performed between June 2024 and June 2025 (n = 731 scans, 616 patients). All imaging reviews and longitudinal lesion tracking were performed by one board-certified neuroradiologist. Adult patients with confirmed brain metastases and at least three MRI examinations (including external studies) were included. We assessed the concordance of routine narrative MRI follow-up reports against a longitudinal review of all available MRIs and treatment timelines, which served as the reference standard. Lesion identity was considered preserved when reports explicitly recognized and linked lesions across time points, and lost when identity was omitted or ambiguous in at least one report. Results: The final cohort comprised 73 patients (477 tracked lesions). More than half of monitored lesions disappeared (42.9%) or evolved into post-treatment sequelae (9.9%), and were omitted from narrative reports, limiting retrospective recognition without prior imaging. The ability of routine reports to preserve lesion identity declined as cases became more complex. Concordance was higher in uniform evolution patterns (≈60%) but dropped to 18.2% in mixed evolution. A similar decline was seen with sequential metastatic waves, defined as new metastases appearing at distinct time points: 65.2% (1 wave), 46.7% (2 waves), 18.2% (3 waves), and complete loss of continuity when >3 waves occurred. Conclusions: Routine narrative MRI follow-up reports generally provide adequate information in simple cases with uniform lesion behavior, but tend to lose critical details as disease trajectories become more complex, particularly in heterogeneous or multi-wave disease. Even when individual lesions are identified across examinations, documentation remains fragmented and reflects only a snapshot of the disease course rather than an integrated longitudinal perspective. These findings highlight a critical vulnerability in current follow-up practices. Improving lesion-level continuity, potentially through AI-assisted tools, may enhance the accuracy, consistency, and clinical utility of MRI surveillance in patients with brain metastases.

Tacaribe virus (TCRV), a New World arenavirus, is associated with neotropical frugivorous bats, particularly Artibeus spp., and is considered to have zoonotic potential. Here, we report the detection of TCRV in multiple biological compartments of a Molossus molossus (velvety free-tailed bat), an insectivorous species commonly found in Brazilian urban ecosystems. Brain tissues negative for rabies were subjected to high-throughput RNA sequencing, revealing a diverse array of viral taxa, including partial L and S segments of TCRV with respective genome coverages of 68.2% and 65.6%. These sequences shared 90% nucleotide identity and 94% amino acid identity with TCRV reference strains. Phylogenetic reconstruction grouped the newly identified TCRV sequences and the TCRV strain A354 (isolated from a Brazilian Artibeus planirostris bat) within a clade that also includes Tietê mammarenavirus strains (Brazilian Carollia perspicillata bat), both of which are genetically divergent members of the Arenaviridae family. The detection of TCRV in M. molossus may indicate previously unrecognized circulation of this virus in insectivorous bats, expanding our understanding of its tissue tropism and host range. This finding is particularly significant given the synanthropic behavior of M. molossus bats and its potential implications for TCRV evolution. Moreover, our results highlight the critical role of untargeted high-throughput sequencing in uncovering overlooked viral diversity, enabling the detection of unexpected pathogens in non-traditional hosts and tissues. While TCRV remains poorly characterized in terms of human pathogenicity, continued surveillance is warranted to assess potential spillover risks. Understanding which animals carry viruses is key to predicting and preventing disease spread. Here, we report the first detection of Tacaribe virus (TCRV), previously found only in fruit-eating bats, in multiple biological compartments, including the brain, of Molossus molossus, an insect-eating bat common in urban areas of Brazil. This finding expands the known range of both the virus and its possible hosts. By confirming this unexpected host-virus association using original tissue samples, our study provides new insights into how TCRV may circulate in nature. While TCRV is not currently considered a major threat to humans, its detection in a new bat species raises important questions about its transmission, evolution, and potential health impacts. These results emphasize the importance of monitoring diverse bat species, including those not traditionally linked to specific viruses, to better assess emerging virus risks in changing environments.

The neurotransmitters vasotocin, oxytocin, dopamine, and serotonin are widely involved in vertebrate social behavior, and changes in their abundance and distribution in the brain have been linked to the evolution of complex sociality. Reptiles provide an excellent system in which to investigate the neural mechanisms of social living. Using immunohistochemistry, we compare distributions of these transmitters in two skinks differing primarily in social ecology: the family-living Liopholis whitii and the solitary Eulpamrus quoyii. We describe patterns of immunopositive signal for both cell bodies and fibers across the entire brain (excluding the olfactory bulbs). In both species, vasotocin and oxytocin were found in the preoptic area, paraventricular nucleus, supraoptic nucleus, dorsomedial hypothalamus, and supraoptic decussation, as well as surrounding the lateral forebrain bundle. Tyrosine hydroxylase (a marker for dopamine) was found in the paraventricular organ nucleus, substantia nigra, and ventral tegmental area, and serotonin was found in the raphe nuclei and superior reticular field. We found novel oxytocin cell groups in the dorsomedial hypothalamus and cerebellum of L. whitii, and novel serotonin signal in the red nucleus of E. quoyii. Immunopositive signals found only in L. whitii also include vasotocin in the ventral tegmental area, tyrosine hydroxylase in the interpeduncular nucleus, and serotonin in the suprachiasmatic nucleus. The qualitatively greater abundance of these transmitters in the family-living L. whitii suggests that these molecules may have played an important role in the evolution of social behavior in these skinks and provides a foundation for broader comparisons across the social skinks.

The vertebrate brain must balance internally generated predictions with constraints of environmental affordances. This balance constitutes a fundamental principle of neural organization that underwrites cortical computation. Using the prosomeric model of the neuraxis, we show how dorsalizing and ventralizing morphogenetic gradients specify excitatory and inhibitory lineages during development, establishing the functional architecture of active affordance. These developmental asymmetries are elaborated through telencephalic expansion, pallial-subpallial integration, and laminar differentiation of the neocortex, as described by the structural model. We demonstrate that motor control emerges within a sensory-predictive architecture due to the alar origin of the telencephalon and that increasing excitatory-inhibitory complementarity within the mammalian neocortex enables selective, context-sensitive action. Subpallial and diencephalic systems provide inhibitory governance over cortical action tendencies, supporting policy evaluation and selection in the framework of active inference. At the base of this hierarchy, the hypothalamus integrates homeostatic and allostatic signals to bias the landscape of affordances, shaping the likelihood of action policies. Together, these findings establish active affordance as a developmental and evolutionary framework linking prosomeric neurodevelopment, cortical architecture, subcortical control, and adaptive behavior. Active inference is thereby situated as the mature cortical expression of a conserved biological solution to acting in an uncertain world.

Humans display larger and more complex parietal lobes, when compared with other primates. The superior parietal lobule is a region still poorly known in terms of comparative and evolutionary neuroanatomy, although at least its medial region, the precuneus, is apparently expanded in our species. In this article, I review 20 years of personal research on the morphology and evolution of this cortical element. The precuneus is particularly variable among adult humans, mostly in its dorsal and anterior areas. This large individual variability seems already settled at birth. During aging, this cortical region is particularly sensitive to atrophy and neurodegeneration. Its ventral areas are embedded in a complicated topological environment, suggesting spatial, metabolic, and vascular constraints. Human and nonhuman primates share a similar organization of the superior parietal lobule, although with different proportions. Even when compared with extinct hominids, the precuneus in modern humans looks more expanded. These changes are expected to be associated with some cognitive variations, possibly involving visuospatial integration, body cognition, mental imaging, and self-construction.

Evolution of novel behavior is reflected in changes in sensory investment or integration, but the exact nature of these changes is often unclear. The Neotropical butterfly tribe, Heliconiini, offer an attractive system for studying how behavioral evolution is facilitated by changes in the neural system. Within the Heliconiini tribe, the genus Heliconius possess fourfold larger mushroom bodies, the insect learning and memory center, than closely related Heliconiini. Mushroom body expansion in Heliconius co-occurred with a dietary innovation, and is associated with systematic spatial foraging and extended lifespan. Heliconius' foraging relies on visual scene memories and, indeed, Heliconius have stable visual long-term memory, and evidence of visual specialization in the mushroom bodies. Here, we explore how vision-specific neuroanatomical and behavioral enhancement in Heliconius impacts sensory pathways upstream of the mushroom bodies by assessing investment across the eyes, sensory neuropils, and projection pathways. Despite evidence of refinement in visually based behavior, we found no increased investment in visual structures, brain areas, or pathways. This suggests that the rapid expansion of the Heliconius mushroom body occurred in a context of conserved detection and processing of visual cues, and that a localized shift within integrative brain centers facilitated the evolution of Heliconius' novel behaviors.

The macaque genus includes 25 species with diverse social systems, ranging from low to high social tolerance grades. Such interspecific behavioral variability provides a unique model to tackle the evolutionary foundation of primate social brain. Yet, the neuroanatomical correlates of these social tolerance grades remain unknown. To address this question, we expressed social tolerance grades within a novel cognitive framework and analyzed post-mortem structural scans from 12 macaque species. Our results show that amygdala volume is a subcortical predictor of macaques' social tolerance, with high tolerance species exhibiting larger amygdala than low tolerance ones. We further investigated the developmental trajectory of amygdala across social grades and found that intolerant species showed a gradual increase in relative amygdala volume across the lifespan. Unexpectedly, tolerant species exhibited a decrease in relative amygdala volume across the lifespan, contrasting with the age-related increase observed in intolerant species-a developmental pattern previously undescribed in primates. Taken together, these findings provide valuable insights into the cognitive, neuroanatomical, and evolutionary basis of primates' social behaviors. Macaque monkeys live under a variety of social regimes. Some species flourish within highly structured, hierarchical societies, while others navigate more tolerant yet less predictable social networks. Primatologists have categorised these social differences, including how often reconciliation occurs after conflicts, into four levels of social tolerance. However, the neuronal mechanisms underlying these social variations remain poorly understood. Closely related species offer a natural laboratory for studying the social brain in primates. To investigate how neural networks may have evolved in response to differing social challenges, Silvère et al. analysed 43 brain scans from 12 macaque species. All data were gathered from animals that had died of natural or accidental causes The scans showed that the relative size of a species’ amygdala – a brain region involved in emotional responses, decision-making, and memory – correlates with its level of social tolerance. For example, low-tolerance species are born with a smaller amygdala, which grows larger with age. Conversely, in more socially tolerant species, the amygdala decreases in size as they age, contrasting with findings in other primates, including humans. These findings imply that living in a more tolerant social environment could impose greater cognitive demands on the brain, with the amygdala possibly playing a part in complex social cognition. In contrast, the volume of a brain region called the hippocampus revealed more variable differences across social grades among macaques, with a more significant effect observed only in individuals aged between 13 and 18 years. Additionally, differences in hippocampal volume also varied among monkeys living in different areas, supporting the idea that certain regions contribute to social cognitive processes in tolerant species, particularly during developmental phases linked to social maturation. Exploring natural variation in brain evolution and function opens new avenues for primate neuroscience. A more extensive comparative analysis across all living primate species could further clarify evolutionary pathways. Moreover, identifying neural networks that are either evolutionarily conserved or highly variable may help shape new research directions aimed at understanding the biological basis of neurodivergence.

Star-nosed moles are renowned as the fastest foragers among mammals, able to identify and eat small prey in less than a quarter of a second. This ability stems in part from the mole's extraordinary mechanosensory star which has been the focus of many investigations. However, fast eating also requires a specialized motor system and associated structures. Here, the mole's unusual incisors are explored as a key adaptation for efficient foraging. High-speed videos of foraging moles, including microscopic views at 1,000 frames per second, were used to measure prey handling time and tooth movements. Scanning electron microscopy was used to assess tooth structure. Specimens from Cornell Museum of Vertebrates were examined with light microscopy. Data from previous investigations were compared to the present results. A mole with worn front teeth was discovered, and this specimen often failed to secure small prey efficiently, thus doubling the mole's handling time compared to normal specimens. The manner in which the worn teeth failed suggested the mole's normal incisors are analogous to a specific type of man-made surgical forceps - so-called Yaşargil tumor forceps. The results reveal an example of serendipitous biomimicry by human surgeons in designing soft tissue forceps, highlight the importance of motor specializations in the star-nosed mole's fast foraging ability, and suggest some of the specific anatomical specialization that are the result of selection on the key variables (space clearance rate and handling time) in Holling's pioneering foraging theory equation.

Endocasts are casts of the internal surface of skull bones created by the brain and surrounding tissues. These fossil phantoms provide the most direct evidence of the brains of extinct organisms, and are one of the many puzzle pieces that help paleoneurologists reconstruct brain evolution. The recent discovery of a small-brained, recently-extinct human species, Homo naledi, creates a timely opportunity to review what endocasts can and cannot tell us about ancient brains. We first review published evidence about the brain and behavior of H. naledi, including the suggestion that the species may have practiced mortuary behaviors over 230,000 years ago. We next use geometric morphometric methods to reconstruct and the most complete H. naledi endocast and compare it to those of modern humans and Pleistocene hominins. Our results corroborate previous evidence that the brain of H. naledi presents a unique combination of ancestral and modern human-like characteristics, specifically displaying a derived frontal lobe while retaining ancestral sizes, morphology, and cerebro-cerebellar proportions. Finally, we discuss these results in the context of recent paleoanthropological data, advances in neuroimaging, and theoretical frameworks linking brain morphology, structure, and function.

Ontogenetic brain growth in cetaceans is essential for understanding their development and evolution. This study investigates brain size changes relative to body growth in bowhead (Balaena mysticetus) and beluga (Delphinapterus leucas) whales in the framework of age estimates of pre- and postnatal specimens. We collected specimens in the field, determined brain size and endocranial volumes, as well as size of endocranial adnexa, either by direct measurement or by CT. We estimated age using baleen length (bowhead), growth layers in teeth (belugas), or fetal stages. We fitted Gompertz growth models to our data. Our findings show that both bowhead and beluga whales reach nearly their full brain size by the end of weaning, unlike dolphins and humans, whose brains continue growing after weaning. Bowhead brains grow faster than those of belugas, and much faster than those of humans, and their rete mirabile occupies a much larger portion of the cranial cavity than in belugas. Encephalization quotients decline with age due to continued body growth after brain maturation. Brain growth in these cetacean species plateaus early, challenging the assumption that cetacean brains grow throughout life. In bowhead, the brain is significantly smaller than the cranial cavity, and this is not the case in beluga. If this observation can be generalized to all mysticetes and odontocetes, it implies that no single equation can capture the proportional volumes of the brain and cranial cavity across the entire cetacean clade.

Seals and sea lions have highly developed volitional breathing control, to which the phocid seals add vocal production learning, including mimicry. In this work, using histology and ex vivo diffusion magnetic resonance imaging tractography, we provide evidence for a phylogenetic spectrum of accumulative neural adaptations supporting aspects of volitional vocal control across pinnipeds. Otariids and phocid seals, but not coyotes, have a direct connection between the vocal motor cortex and phonatory brainstem nuclei. Harbor seals showed hypertrophic connectivity between the anterior ventrolateral thalamus and the vocal premotor cortex-part of a forebrain circuit related to vocal learning in birds and mimicry in humans and parrots. We demonstrate that phocid seals have auditory-premotor pathways potentially related to developmental call learning.

Neuron size varies significantly over evolution, contributing to diverse nervous systems of variable complexity, while aberrant neuron size is associated with neurodevelopmental and degenerative diseases. How do neuron cell body and neurite size and organization impact nervous system development and function? To systematically study the effects of neuron size on the vertebrate nervous system, we characterized triploid Xenopus tadpoles, which possess a 1.5-fold increase in genome size compared with diploids. Triploid neurons displayed a scaling increase in total volume and a superscaling increase in membrane surface area. Imaging, flow cytometry, and RNA sequencing analyses revealed that triploid brains were morphologically and transcriptionally similar to diploid brains but less proliferative, containing fewer neurons and displaying increased global activity. Interestingly, physiological differences at the neuron and nervous system levels affected swimming behavior in tadpoles. Our findings thus establish a framework to link genome size, neuron size, and nervous system development and function in vertebrates.

Baird's beaked whale, a member of the family Ziphiidae, is one of the largest odontocetes, second only in body mass to the sperm whale. Baird's beaked whales are known for their ability to dive to exceptional depths; however, this behavior makes them difficult to observe in their natural habitat and has resulted in major gaps in our understanding of the species. To address part of this gap, this study provides a comprehensive description of the Baird's beaked whale brain using magnetic resonance imaging (MRI). We describe the external and internal neuroanatomy, including sulcal and gyral patterns, and provide quantitative measurements of the cerebral cortex, amygdala, hippocampus, ventricular system, superior and inferior colliculi, cerebellum, the mid-sagittal cross-sectional area of the corpus callosum, the gyrification index, and encephalization quotient. Baird's beaked whale has a brain organization typical of odontocetes, including a large, exceptionally gyrencephalic neocortex. Both the encephalization quotient and the relative cerebellar volume are lower than in delphinids, consistent with findings in other deep-diving cetaceans. These differences may reflect energy allocation strategies related to diving behavior and body size. By contextualizing these traits within a broader mammalian neuroanatomical framework, this study contributes to our understanding of how ecological pressures may shape brain evolution, particularly in rarely-studied cetacean lineages like the Ziphiidae.