Marmosets as model systems for the study of Alzheimer's disease and related dementias: substantiation of physiological Tau 3R and 4R isoform expression and phosphorylation.

INTRODUCTION: Marmosets have been shown to spontaneously develop pathological hallmarks of Alzheimer's disease (AD) during advanced age, including amyloid-beta plaques, positioning them as a model system to overcome the rodent-to-human translational gap for AD. However, Tau expression in the marmoset brain has been understudied. METHODS: To comprehensively investigate Tau isoform expression in marmosets, brain tissue from eight unrelated marmosets across various ages was evaluated and compared to human postmortem AD tissue. Microtubule-associated protein tau ( MAPT ) mRNA expression and splicing were confirmed by RT-PCR. Tau isoforms in the marmoset brain were examined by western blot, mass spectrometry, immunofluorescence, and immunohistochemical staining. Synaptic Tau expression was analyzed from crude synaptosome extractions. RESULTS: 3R and 4R Tau isoforms are expressed in marmoset brains at both transcript and protein levels across ages. Results from western blot analysis were confirmed by mass spectrometry, which revealed that Tau peptides in marmoset corresponded to the 3R and 4R peptides in the human AD brain. 3R Tau was primarily enriched in neonate brains, and 4R enhanced in adult and aged brains. Tau was widely distributed in neurons with localization in the soma and synaptic regions. Phosphorylation residues were observed on Thr-181, Thr-217, and Thr-231, Ser202/Thr205, Ser396/Ser404. Paired helical filament (PHF)-like aggregates were also detected in aged marmosets. DISCUSSION: Our results confirm the expression of both 3R and 4R Tau isoforms and important phosphorylation residues in the marmoset brain. These data emphasize the significance of marmosets with natural expression of AD-related hallmarks as important translational models for the study of AD.

Early molecular events of autosomal-dominant Alzheimer's disease in marmosets with PSEN1 mutations.

INTRODUCTION: Fundamental questions remain about the key mechanisms that initiate Alzheimer's disease (AD) and the factors that promote its progression. Here we report the successful generation of the first genetically engineered marmosets that carry knock-in (KI) point mutations in the presenilin 1 (PSEN1) gene that can be studied from birth throughout lifespan. METHODS: CRISPR/Cas9 was used to generate marmosets with C410Y or A426P point mutations in PSEN1. Founders and their germline offspring are comprehensively studied longitudinally using non-invasive measures including behavior, biomarkers, neuroimaging, and multiomics signatures. RESULTS: Prior to adulthood, increases in plasma amyloid beta were observed in PSEN1 mutation carriers relative to non-carriers. Analysis of brain revealed alterations in several enzyme-substrate interactions within the gamma secretase complex prior to adulthood. DISCUSSION: Marmosets carrying KI point mutations in PSEN1 provide the opportunity to study the earliest primate-specific mechanisms that contribute to the molecular and cellular root causes of AD onset and progression. HIGHLIGHTS: We report the successful generation of genetically engineered marmosets harboring knock-in point mutations in the PSEN1 gene. PSEN1 marmosets and their germline offspring recapitulate the early emergence of AD-related biomarkers. Studies as early in life as possible in PSEN1 marmosets will enable the identification of primate-specific mechanisms that drive disease progression.

Impact of COVID-19 on the degree of compliance with hand hygiene: a repeated cross-sectional study.

Hand hygiene (HH) is the paramount measure used to prevent healthcare-associated infections. A repeated cross-sectional study was undertaken with direct observation of the degree of compliance on HH of healthcare personnel during the SARS-CoV-2 pandemic. Between, 2018-2019, 9,083 HH opportunities were considered, and 5,821 in 2020-2022. Chi squared tests were used to identify associations. The crude and adjusted odds ratios were used along with a logistic regression model for statistical analyses. Compliance on HH increased significantly (p < 0.001) from 54.5% (95% CI: 53.5, 55.5) to 70.1% (95% CI: 68.9, 71.2) during the COVID-19 pandemic. This increase was observed in four of the five key moments of HH established by the World Health Organization (WHO) (p < 0.05), except at moment 4. The factors that were significantly and independently associated with compliance were the time period considered, type of healthcare-personnel, attendance at training sessions, knowledge of HH and WHO guidelines, and availability of hand disinfectant alcoholic solution in pocket format. Highest HH compliance occurred during the COVID-19 pandemic, reflecting a positive change in healthcare-personnel's behaviour regarding HH recommendations.

Effectiveness of influenza vaccine in preventing severe cases of influenza: Season 2022/2023.

INTRODUCTION: Influenza poses a significant burden in terms of morbidity and mortality, with vaccination being one of the most effective measures for its prevention. Therefore, the aim of this study is to determine the effectiveness of the influenza vaccine in preventing cases of severe influenza in patients admitted to a tertiary hospital during the 2022/23 season. METHODS: Case-control study. All hospitalised patients with a positive result in an RT-PCR for influenza were included. Those who met the criteria for a severe case (pneumonia, sepsis, multi-organ failure, admission to ICU or exitus) were considered cases. Those who did not meet these criteria were considered controls. Vaccine effectiveness (VE) to prevent severe cases and its 95% confidence interval were calculated. RESULTS: A total of 403 patients were admitted with confirmed influenza. Of these, 98 (24.3%) developed severe influenza. Of the total, 50.6% were men and 47.1% were over 65 years of age. VE adjusted for influenza type, age and certain comorbidities was 40.6% (-21.9 to 71.1). In a segmented analysis, influenza vaccine was effective in preventing severe cases in all categories. It was particularly relevant in the 65+ age group (VEa = 60.9%; -2.0 to 85.0) and in patients with influenza A (VEa = 56.7%; 1.5-80.9). CONCLUSION: Influenza vaccination markedly reduced the occurrence of severe cases of influenza in hospitalised patients, therefore, it remains the main strategy to reduce morbidity and mortality and associated costs.

Improving preclinical to clinical translation of cognitive function for aging-related disorders: the utility of comprehensive touchscreen testing batteries in common marmosets.

Concerns about poor animal to human translation have come increasingly to the fore, in particular with regards to cognitive improvements in rodent models, which have failed to translate to meaningful clinical benefit in humans. This problem has been widely acknowledged, most recently in the field of Alzheimer's disease, although this issue pervades the spectrum of central nervous system (CNS) disorders, including neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. Consequently, recent efforts have focused on improving preclinical to clinical translation by incorporating more clinically analogous outcome measures of cognition, such as touchscreen-based assays, which can be employed across species, and have great potential to minimize the translational gap. For aging-related research, it also is important to incorporate model systems that facilitate the study of the long prodromal phase in which cognitive decline begins to emerge and which is a major limitation of short-lived species, such as laboratory rodents. We posit that to improve translation of cognitive function and dysfunction, nonhuman primate models, which have conserved anatomical and functional organization of the primate brain, are necessary to move the field of translational research forward and to bridge the translational gaps. The present studies describe the establishment of a comprehensive battery of touchscreen-based tasks that capture a spectrum of domains sensitive to detecting aging-related cognitive decline, which will provide the greatest benefit through longitudinal evaluation throughout the prolonged lifespan of the marmoset.

Direct interhemispheric cortical communication via thalamic commissures: a new white matter pathway in the primate brain.

Cortical neurons of eutherian mammals project to the contralateral hemisphere, crossing the midline primarily via the corpus callosum and the anterior, posterior, and hippocampal commissures. We recently reported and named the thalamic commissures (TCs) as an additional interhemispheric axonal fiber pathway connecting the cortex to the contralateral thalamus in the rodent brain. Here, we demonstrate that TCs also exist in primates and characterize the connectivity of these pathways with high-resolution diffusion-weighted MRI, viral axonal tracing, and fMRI. We present evidence of TCs in both New World (Callithrix jacchus and Cebus apella) and Old World primates (Macaca mulatta). Further, like rodents, we show that the TCs in primates develop during the embryonic period, forming anatomical and functionally active connections of the cortex with the contralateral thalamus. We also searched for TCs in the human brain, showing their presence in humans with brain malformations, although we could not identify TCs in healthy subjects. These results pose the TCs as a vital fiber pathway in the primate brain, allowing for more robust interhemispheric connectivity and synchrony and serving as an alternative commissural route in developmental brain malformations.

Noninvasive disruption of the blood-brain barrier in the marmoset monkey.

The common marmoset monkey (Callithrix jacchus) is a species of rising prominence in the neurosciences due to its small size, ease of handling, fast breeding, and its shared functional and structural brain characteristics with Old World primates. With increasing attention on modeling human brain diseases in marmosets, understanding how to deliver therapeutic or neurotropic agents to the marmoset brain noninvasively is of great preclinical importance. In other species, including humans, transcranial focused ultrasound (tFUS) aided by intravenously injected microbubbles has proven to be a transient, reliable, and safe method for disrupting the blood-brain barrier (BBB), allowing the focal passage of therapeutic agents that do not otherwise readily traverse the tight endothelial junctions of the BBB. The critical gap that we address here is to document parameters to disrupt the BBB reliably and safely in marmosets using tFUS. By integrating our marmoset brain atlases and the use of a marmoset-specific stereotactic targeting system, we conduct a series of systematic transcranial sonication experiments in nine marmosets. We demonstrate the effects of center frequency, acoustic pressure, burst period, and duration, establish a minimum microbubble dose, estimate microbubble clearance time, and estimate the duration that the BBB remains open to passage. Successful BBB disruption is reported in vivo with MRI-based contrast agents, as well as Evans blue staining assessed ex vivo. Histology (Hematoxylin and Eosin staining) and immunohistochemistry indicate that the BBB can be safely and reliably opened with the parameters derived from these experiments. The series of experiments presented here establish methods for safely, reproducibly, and focally perturbing the BBB using tFUS in the common marmoset monkey that can serve as a basis for noninvasive delivery of therapeutic or neurotropic agents.

Bridging the rodent to human translational gap: Marmosets as model systems for the study of Alzheimer's disease.

Introduction: Our limited understanding of the mechanisms that trigger the emergence of Alzheimer's disease (AD) has contributed to the lack of interventions that stop, prevent, or fully treat this disease. We believe that the development of a non-human primate model of AD will be an essential step toward overcoming limitations of other model systems and is crucial for investigating primate-specific mechanisms underlying the cellular and molecular root causes of the pathogenesis and progression of AD. Methods: A new consortium has been established with funding support from the National Institute on Aging aimed at the generation, characterization, and validation of Marmosets As Research Models of AD (MARMO-AD). This consortium will study gene-edited marmoset models carrying genetic risk for AD and wild-type genetically diverse aging marmosets from birth throughout their lifespan, using non-invasive longitudinal assessments. These include characterizing the genetic, molecular, functional, behavioral, cognitive, and pathological features of aging and AD. Results: The consortium successfully generated viable founders carrying PSEN1 mutations in C410Y and A426P using CRISPR/Cas9 approaches, with germline transmission demonstrated in the C410Y line. Longitudinal characterization of these models, their germline offspring, and normal aging outbred marmosets is ongoing. All data and resources from this consortium will be shared with the greater AD research community. Discussion: By establishing marmoset models of AD, we will be able to investigate primate-specific cellular and molecular root causes that underlie the pathogenesis and progression of AD, overcome limitations of other model organisms, and support future translational studies to accelerate the pace of bringing therapies to patients.

Integrated Design Fabrication and Control of a Bioinspired Multimaterial Soft Robotic Hand.

Machines that mimic humans have inspired scientists for centuries. Bioinspired soft robotic hands are a good example of such an endeavor, featuring intrinsic material compliance and continuous motion to deal with uncertainty and adapt to unstructured environments. Recent research led to impactful achievements in functional designs, modeling, fabrication, and control of soft robots. Nevertheless, the full realization of life-like movements is still challenging to achieve, often based on trial-and-error considerations from design to fabrication, consuming time and resources. In this study, a soft robotic hand is proposed, composed of soft actuator cores and an exoskeleton, featuring a multimaterial design aided by finite element analysis (FEA) to define the hand geometry and promote finger's bendability. The actuators are fabricated using molding, and the exoskeleton is 3D-printed in a single step. An ON-OFF controller keeps the set fingers' inner pressures related to specific bending angles, even in the presence of leaks. The FEA numerical results were validated by experimental tests, as well as the ability of the hand to grasp objects with different shapes, weights, and sizes. This integrated solution will make soft robotic hands more available to people, at a reduced cost, avoiding the time-consuming design-fabrication trial-and-error processes.

Direct interhemispheric cortical communication via thalamic commissures: a new white-matter pathway in the primate brain.

Cortical neurons of eutherian mammals project to the contralateral hemisphere, crossing the midline primarily via the corpus callosum and the anterior, posterior, and hippocampal commissures. We recently reported an additional commissural pathway in rodents, termed the thalamic commissures (TCs), as another interhemispheric axonal fiber pathway that connects cortex to the contralateral thalamus. Here, we demonstrate that TCs also exist in primates and characterize the connectivity of these pathways with high-resolution diffusion-weighted magnetic resonance imaging, viral axonal tracing, and functional MRI. We present evidence of TCs in both New World (Callithrix jacchus and Cebus apella) and Old World primates (Macaca mulatta). Further, like rodents, we show that the TCs in primates develop during the embryonic period, forming anatomical and functionally active connections of the cortex with the contralateral thalamus. We also searched for TCs in the human brain, showing their presence in humans with brain malformations, although we could not identify TCs in healthy subjects. These results pose the TCs as an important fiber pathway in the primate brain, allowing for more robust interhemispheric connectivity and synchrony and serving as an alternative commissural route in developmental brain malformations.

Heterotopic connectivity of callosal dysgenesis in mice and humans.

The corpus callosum (CC), the largest brain commissure and the primary white matter pathway for interhemispheric cortical connectivity, was traditionally viewed as a predominantly homotopic structure, connecting mirror areas of the cortex. However, new studies verified that most callosal commissural fibers are heterotopic. Recently, we reported that ~75% of the callosal connections in the brains of mice, marmosets, and humans are heterotopic, having an essential role in determining the global properties of brain networks. In the present study, we leveraged high-resolution diffusion-weighted imaging and graph network modeling to investigate the relationship between heterotopic and homotopic callosal fibers in human subjects and in a spontaneous mouse model of Corpus Callosum Dysgenesis (CCD), a congenital developmental CC malformation that leads to widespread whole-brain reorganization. Our results show that the CCD brain is more heterotopic than the normotypical brain, with both mouse and human CCD subjects displaying highly variable heterotopicity maps. CCD mice have a clear heterotopicity cluster in the anterior CC, while hypoplasic humans have strongly variable patterns. Graph network-based connectivity profile showed a direct impact of heterotopic connections on CCD brains altering several network-based statistics. Our collective results show that CCD directly alters heterotopic connections and brain connectivity.

Improvement and validation of a female finite element model of the cervical spine.

Although the cervical spine supports and controls the kinematics of the head, it is vulnerable to injuries during mechanical loading. Severe injuries often result in damage to the spinal cord, leading to significant ramifications. The role of gender in determining the outcome of such injuries has been established as significant. In order to better understand the essential mechanics and develop treatments or preventative measures, various forms of research have been conducted. Computational modelling is one of the most useful and extensively utilised methods, as it provides information that would otherwise be difficult to obtain. As such, the primary goal of this research is to create a new finite element of the female cervical spine that will more accurately represent the group most affected by such injuries. This work is a continuation of a previous study where a model was created from the computer tomography scans of a 46-year-old female. A functioning spinal unit consisting of the C6-C7 segment was simulated as a validation procedure. The experimental data obtained from cadaveric specimens, that assessed the range of motion of different cervical segments in flexion-extension, axial rotation, and lateral bending, was used to validate the reduced model.

In vivo MRI is sensitive to remyelination in a nonhuman primate model of multiple sclerosis.

Remyelination is crucial to recover from inflammatory demyelination in multiple sclerosis (MS). Investigating remyelination in vivo using magnetic resonance imaging (MRI) is difficult in MS, where collecting serial short-interval scans is challenging. Using experimental autoimmune encephalomyelitis (EAE) in common marmosets, a model of MS that recapitulates focal cerebral inflammatory demyelinating lesions, we investigated whether MRI is sensitive to, and can characterize, remyelination. In six animals followed with multisequence 7 T MRI, 31 focal lesions, predicted to be demyelinated or remyelinated based on signal intensity on proton density-weighted images, were subsequently assessed with histopathology. Remyelination occurred in four of six marmosets and 45% of lesions. Radiological-pathological comparison showed that MRI had high statistical sensitivity (100%) and specificity (90%) for detecting remyelination. This study demonstrates the prevalence of spontaneous remyelination in marmoset EAE and the ability of in vivo MRI to detect it, with implications for preclinical testing of pro-remyelinating agents.

Mapping the hepatic immune landscape identifies monocytic macrophages as key drivers of steatohepatitis and cholangiopathy progression.

BACKGROUND AND AIMS: The progression of chronic liver diseases towards liver cirrhosis is accompanied by drastic tissue changes. This study combines elaborate transcriptomic and histological methods aiming at spatially resolving the hepatic immune microenvironment in NAFLD (including NASH, primary sclerosing cholangitis, primary biliary cholangitis, and severe alcoholic hepatitis). APPROACH AND RESULTS: Human liver samples were subjected to RNA-sequencing (n=225) and imaging cytometry (n=99) across 3 independent patient cohorts. Liver samples from alcoholic hepatitis and primary biliary cholangitis patients were used for comparison. Myeloid populations were further characterized in corresponding mouse models. Imaging, clinical, and phenotypical data were combined for multidimensional analysis. NAFLD/NASH and primary sclerosing cholangitis disease stages were associated with loss of parenchymal areas, increased ductular cell accumulation, and infiltration of immune cells. NASH patients predominantly exhibited myeloid cell accumulation, whereas primary sclerosing cholangitis patients additionally had pronounced lymphoid cell responses. Correlating to disease stage, both etiologies displayed intense IBA1 + CD16 low CD163 low macrophage aggregation in nonparenchymal areas, with a distinct spatial proximity to ductular cells. Mouse models revealed that disease-associated IBA1 + hepatic macrophages originated from bone marrow-derived monocytes. Using an unbiased, machine learning-based algorithm, IBA1 in combination with hepatocyte and ductular cell immunostaining-predicted advanced cirrhosis in human NASH, primary sclerosing cholangitis, and alcoholic hepatitis. CONCLUSIONS: Loss of hepatocytes and increased ductular reaction are tightly associated with monocyte-derived macrophage accumulation and represent the most prominent common immunological feature revealing the progression of NAFLD, primary sclerosing cholangitis, primary biliary cholangitis, and alcoholic hepatitis, suggesting IBA1 + CD163 low macrophages are key pathogenic drivers of human liver disease progression across diverse etiologies.

The relevance of heterotopic callosal fibers to interhemispheric connectivity of the mammalian brain.

The corpus callosum (CC) is the largest white matter structure and the primary pathway for interhemispheric brain communication. Investigating callosal connectivity is crucial to unraveling the brain's anatomical and functional organization in health and disease. Classical anatomical studies have characterized the bulk of callosal axonal fibers as connecting primarily homotopic cortical areas. Whenever detected, heterotopic callosal fibers were ascribed to altered sprouting and pruning mechanisms in neurodevelopmental diseases such as CC dysgenesis (CCD). We hypothesized that these heterotopic connections had been grossly underestimated due to their complex nature and methodological limitations. We used the Allen Mouse Brain Connectivity Atlas and high-resolution diffusion-weighted imaging to identify and quantify homotopic and heterotopic callosal connections in mice, marmosets, and humans. In all 3 species, we show that ~75% of interhemispheric callosal connections are heterotopic and comprise the central core of the CC, whereas the homotopic fibers lay along its periphery. We also demonstrate that heterotopic connections have an essential role in determining the global properties of brain networks. These findings reshape our view of the corpus callosum's role as the primary hub for interhemispheric brain communication, directly impacting multiple neuroscience fields investigating cortical connectivity, neurodevelopment, and neurodevelopmental disorders.

An integrated resource for functional and structural connectivity of the marmoset brain.

Comprehensive integration of structural and functional connectivity data is required to model brain functions accurately. While resources for studying the structural connectivity of non-human primate brains already exist, their integration with functional connectivity data has remained unavailable. Here we present a comprehensive resource that integrates the most extensive awake marmoset resting-state fMRI data available to date (39 marmoset monkeys, 710 runs, 12117 mins) with previously published cellular-level neuronal tracing data (52 marmoset monkeys, 143 injections) and multi-resolution diffusion MRI datasets. The combination of these data allowed us to (1) map the fine-detailed functional brain networks and cortical parcellations, (2) develop a deep-learning-based parcellation generator that preserves the topographical organization of functional connectivity and reflects individual variabilities, and (3) investigate the structural basis underlying functional connectivity by computational modeling. This resource will enable modeling structure-function relationships and facilitate future comparative and translational studies of primate brains.

Frontoparietal connectivity as a product of convergent evolution in rodents and primates: functional connectivity topologies in grey squirrels, rats, and marmosets.

Robust frontoparietal connectivity is a defining feature of primate cortical organization. Whether mammals outside the primate order, such as rodents, possess similar frontoparietal functional connectivity organization is a controversial topic. Previous work has primarily focused on comparing mice and rats to primates. However, as these rodents are nocturnal and terrestrial, they rely much less on visual input than primates. Here, we investigated the functional cortical organization of grey squirrels which are diurnal and arboreal, thereby better resembling primate ecology. We used ultra-high field resting-state fMRI data to compute and compare the functional connectivity patterns of frontal regions in grey squirrels (Sciurus carolinensis), rats (Rattus norvegicus), and marmosets (Callithrix jacchus). We utilized a fingerprinting analysis to compare interareal patterns of functional connectivity from seeds across frontal cortex in all three species. The results show that grey squirrels, but not rats, possess a frontoparietal connectivity organization that resembles the connectivity pattern of marmoset lateral prefrontal cortical areas. Since grey squirrels and marmosets have acquired an arboreal way of life but show no common arboreal ancestor, the expansion of the visual system and the formation of a frontoparietal connectivity architecture might reflect convergent evolution driven by similar ecological niches in primates and tree squirrels.

Robot Assisted Neurosurgery for High-Accuracy, Minimally-Invasive Deep Brain Electrophysiology in Monkeys.

Traditional methods to access subcortical structures involve the use of anatomical atlases and high precision stereotaxic frames but suffer from significant variations in implantation accuracy. Here, we leveraged the use of the ROSA One(R) Robot Assistance Platform in non-human primates to study electrophysiological interactions of the corticospinal tract with spinal cord circuits. We were able to target and stimulate the corticospinal tract within the internal capsule with high accuracy and efficiency while recording spinal local field potentials and multi-unit spikes. Our method can be extended to any subcortical structure and allows implantation of multiple deep brain stimulation probes at the same time. Clinical Relevance- Our method will allow us to elucidate further roles of the corticospinal tract and its interactions with other processing centers in intact animals and in motor syndromes in the future.

Household outbreak of sporotrichosis: towards the One Health approach.

Although sporotrichosis requires a broad approach for control, few reports have described the relationship between the index case and secondary contacts. In the present work, we report an outbreak involving a woman, a dog, and two cats from the same household environment, including the clinical and epidemiological aspects and outcomes, and discuss the importance of a One Health approach to face this neglected disease. The joint efforts of professionals such as veterinarians and physicians are essential for early diagnosis and surveillance, which contributes to the rapid identification and control of zoonotic sporotrichosis outbreaks.

An open access resource for functional brain connectivity from fully awake marmosets.

The common marmoset (Callithrix jacchus) is quickly gaining traction as a premier neuroscientific model. However, considerable progress is still needed in understanding the functional and structural organization of the marmoset brain to rival that documented in longstanding preclinical model species, like mice, rats, and Old World primates. To accelerate such progress, we present the Marmoset Functional Brain Connectivity Resource (marmosetbrainconnectome.org), currently consisting of over 70 h of resting-state fMRI (RS-fMRI) data acquired at 500 µm isotropic resolution from 31 fully awake marmosets in a common stereotactic space. Three-dimensional functional connectivity (FC) maps for every cortical and subcortical gray matter voxel are stored online. Users can instantaneously view, manipulate, and download any whole-brain functional connectivity (FC) topology (at the subject- or group-level) along with the raw datasets and preprocessing code. Importantly, researchers can use this resource to test hypotheses about FC directly - with no additional analyses required - yielding whole-brain correlations for any gray matter voxel on demand. We demonstrate the resource's utility for presurgical planning and comparison with tracer-based neuronal connectivity as proof of concept. Complementing existing structural connectivity resources for the marmoset brain, the Marmoset Functional Brain Connectivity Resource affords users the distinct advantage of exploring the connectivity of any voxel in the marmoset brain, not limited to injection sites nor constrained by regional atlases. With the entire raw database (RS-fMRI and structural images) and preprocessing code openly available for download and use, we expect this resource to be broadly valuable to test novel hypotheses about the functional organization of the marmoset brain.