With increasing numbers of magnetic resonance imaging (MRI) datasets becoming publicly available, researchers and clinicians alike have turned to automated methods of segmentation to enable population-level analyses of these data. Although prior research has evaluated the extent to which automated methods recapitulate \"gold standard\" manual segmentation methods in the human brain, such an evaluation has not yet been carried out for segmentation of MRIs of the macaque brain. Macaques offer the important opportunity to bridge gaps between microanatomical studies using invasive methods like tract tracing, neural recordings, and high-resolution histology and non-invasive macroanatomical studies using methods like MRI. As such, it is important to evaluate whether automated tools derive data of sufficient quality from macaque MRIs to bridge these gaps. We tested the relationship between automated registration-based segmentation using an open source and actively maintained NHP imaging analysis pipeline (AFNI) and gold standard manual segmentation of 4 structures (2 cortical: anterior cingulate cortex and insula; 2 subcortical: amygdala and caudate) across 37 rhesus macaques (Macaca mulatta). We identified some variability in the strength of correlation between automated and manual segmentations across neural regions and differences in relationships with demographic variables like age and sex between the two techniques.

Experimental access to cell types within the mammalian spinal cord is severely limited by the availability of genetic tools. To enable access to lower motor neurons (LMNs) and LMN subtypes, which function to integrate information from the brain and control movement through direct innervation of effector muscles, we generated single cell multiome datasets from mouse and macaque spinal cords and discovered putative enhancers for each neuronal population. We cloned these enhancers into adeno-associated viral vectors (AAVs) driving a reporter fluorophore and functionally screened them in mouse. The most promising candidate enhancers were then extensively characterized using imaging and molecular techniques and further tested in rat and macaque to show conservation of LMN labeling. Additionally, we combined enhancer elements into a single vector to achieve simultaneous labeling of upper motor neurons (UMNs) and LMNs. This unprecedented LMN toolkit will enable future investigations of cell type function across species and potential therapeutic interventions for human neurodegenerative diseases.

As humans age, some experience cognitive impairment while others do not. When impairment does occur, it is not expressed uniformly across cognitive domains and varies in severity across individuals. Translationally relevant model systems are critical for understanding the neurobiological drivers of this variability, which is essential to uncovering the mechanisms underlying the brain\'s susceptibility to the effects of aging. As such, non-human primates are particularly important due to shared behavioral, neuroanatomical, and age-related neuropathological features with humans. For many decades, macaque monkeys have served as the primary non-human primate model for studying the neurobiology of cognitive aging. More recently, the common marmoset has emerged as an advantageous model for this work due to its short lifespan that facilitates longitudinal studies. Despite their growing popularity as a model, whether marmosets exhibit patterns of age-related cognitive impairment comparable to those observed in macaques and humans remains unexplored. To address this major limitation for the development and evaluation of the marmoset as a model of cognitive aging, we directly compared working memory ability as a function of age in macaques and marmosets on the identical working memory task. Our results demonstrate that marmosets and macaques exhibit remarkably similar age-related working memory deficits, highlighting the value of the marmoset as a model for cognitive aging research within the neuroscience community.

To determine whether post-natal improvements in form vision result from changes in mid-level visual cortex, we studied neuronal and behavioral responses to texture stimuli that were matched in local spectral content but varied in \"naturalistic\" structure. We made longitudinal measurements of visual behavior from 16 to 95 weeks of age, and of neural responses from 20 to 56 weeks. We also measured behavioral and neural responses in near-adult animals more than 3 years old. Behavioral sensitivity reached half-maximum around 25 weeks of age, but neural sensitivities remained stable through all ages tested. Neural sensitivity to naturalistic structure was highest in V4, lower in V2 and inferotemporal cortex (IT), and barely discernible in V1. Our results show a dissociation between stable neural performance and improving behavioral performance, which may reflect improved processing capacity in circuits downstream of visual cortex.

OBJECTIVE: The objective of this study was to develop and evaluate the feasibility and safety of a novel transaxial surgical approach for the delivery of human induced pluripotent stem cell-derived dopaminergic neuroprogenitor cells (DANPCs) into the putamen nucleus using nonhuman primates and surgical techniques and tools relevant to human clinical translation.
METHODS: Nine immunosuppressed, unlesioned adult cynomolgus macaques (4 females, 5 males) received intraputaminal injections of vehicle or DANPCs (0.9 × 105 to 1.1 × 105 cells/µL) under real-time intraoperative MRI guidance. The infusates were combined with 1-mM gadoteridol (for intraoperative MRI visualization) and delivered via two tracks per hemisphere (ventral and dorsal) using a transaxial approach. The total volumes of infusion were 25 µL and 50 µL for the right and left putamen, respectively (infusion rate 2.5 µL/min). Animals were evaluated with a battery of clinical and behavioral outcome measures and euthanized 7 or 30 days postsurgery; full necropsies were performed by a board-certified veterinary pathologist. Brain tissues were collected and processed for immunohistochemistry, including against the human-specific marker STEM121.
RESULTS: The optimized surgical technique and tools produced successful targeting of the putamen via the transaxial approach. Intraoperative MR images confirmed on-target intraputaminal injections in all animals. All animals survived to scheduled termination without clinical evidence of neurological deficits. The first 4 animals to undergo surgery had mild brain swelling noted at the end of surgery, of which 3 had transient reduced vision; administration of mannitol therapy and reduced intravenous fluid during the surgical procedure addressed these complications. Immunostaining against STEM121 confirmed the presence of grafted cells along the injection track within the targeted putamen area of DANPC-treated animals. All adverse histological findings were limited in scope and consistent with surgical manipulation, injection procedure, and postsurgical inflammatory response to the mechanical disruption caused by the cannula insertion.
CONCLUSIONS: The delivery system, injection procedure, and DANPCs were well tolerated in all animals. Prevention of mild brain swelling by mannitol dosing and reduction of intravenous fluids during surgery allowed visual effects to be avoided. The results of the study established that this novel transaxial approach can be used to correctly and safely target cell injections to the postcommissural putamen and support clinical investigation.

The role of gamma rhythm (30-80 Hz) in visual processing is debated; stimuli like gratings and hue patches generate strong gamma, but many natural images do not. Could image gamma responses be predicted by approximating images as gratings or hue patches? Surprisingly, this question remains unanswered, since the joint dependence of gamma on multiple features is poorly understood. We recorded local field potentials and electrocorticogram from two female monkeys while presenting natural images and parametric stimuli varying along several feature dimensions. Gamma responses to different grating/hue features were separable, allowing for a multiplicative model based on individual features. By fitting a hue patch to the image around the receptive field, this simple model could predict gamma responses to chromatic images across scales with reasonably high accuracy. Our results provide a simple \"baseline\" model to predict gamma from local image properties, against which more complex models of natural vision can be tested.

Converging data show that exposure to maternal immune activation (MIA) in utero alters brain development in animals and increases the risk of neurodevelopmental disorders in humans. A recently developed non-human primate MIA model affords opportunities for studies with uniquely strong translational relevance to human neurodevelopment. The current longitudinal study used 1H-MRS to investigate the developmental trajectory of prefrontal cortex metabolites in male rhesus monkey offspring of dams (n = 14) exposed to a modified form of the inflammatory viral mimic, polyinosinic:polycytidylic acid (Poly IC), in the late first trimester. Brain metabolites in these animals were compared to offspring of dams that received saline (n = 10) or no injection (n = 4). N-acetylaspartate (NAA), glutamate, creatine, choline, myo-inositol, taurine, and glutathione were estimated from PRESS and MEGA-PRESS acquisitions obtained at 6, 12, 24, 36, and 45 months of age. Prior investigations of this cohort reported reduced frontal cortical gray and white matter and subtle cognitive impairments in MIA offspring. We hypothesized that the MIA-induced neurodevelopmental changes would extend to abnormal brain metabolite levels, which would be associated with the observed cognitive impairments. Prefrontal NAA was significantly higher in the MIA offspring across all ages (p < 0.001) and was associated with better performance on the two cognitive measures most sensitive to impairment in the MIA animals (both p < 0.05). Myo-inositol was significantly lower across all ages in MIA offspring but was not associated with cognitive performance. Taurine was elevated in MIA offspring at 36 and 45 months. Glutathione did not differ between groups. MIA exposure in male non-human primates is associated with altered prefrontal cortex metabolites during childhood and adolescence. A positive association between elevated NAA and cognitive performance suggests the hypothesis that elevated NAA throughout these developmental stages reflects a protective or resilience-related process in MIA-exposed offspring. The potential relevance of these findings to human neurodevelopmental disorders is discussed.

Recombinant adeno-associated virus (rAAV) vector gene delivery systems have demonstrated great promise in clinical trials but continue to face durability and dose-related challenges. Unlike rAAV gene therapy, integrating gene addition approaches can provide curative expression in mitotically active cells and pediatric populations. We explored a novel in vivo delivery approach based on an engineered transposase, Sleeping Beauty (SB100X), delivered as an mRNA within a lipid nanoparticle (LNP), in combination with an rAAV-delivered transposable transgene. This combinatorial approach achieved correction of ornithine transcarbamylase deficiency in the neonatal Spfash mouse model following a single delivery to dividing hepatocytes in the newborn liver. Correction remained stable into adulthood, while a conventional rAAV approach resulted in a return to the disease state. In non-human primates, integration by transposition, mediated by this technology, improved gene expression 10-fold over conventional rAAV-mediated gene transfer while requiring 5-fold less vector. Additionally, integration site analysis confirmed a random profile while specifically targeting TA dinucleotides across the genome. Together, these findings demonstrate that transposable elements can improve rAAV-delivered therapies by lowering the vector dose requirement and associated toxicity while expanding target cell types.

Object recognition often involves the brain segregating objects from their surroundings. Neurophysiological studies of figure-ground texture segregation have yielded inconsistent results, particularly on whether V1 neurons can perform figure-ground texture segregation or just detect texture borders. To address this issue from a population perspective, we utilized two-photon calcium imaging to simultaneously record the responses of large samples of V1 and V4 neurons to figure-ground texture stimuli in awake, fixating macaques. The average response changes indicate that V1 neurons mainly detect texture borders, while V4 neurons are involved in figure-ground segregation. However, population analysis (SVM decoding of PCA-transformed neuronal responses) reveal that V1 neurons not only detect figure-ground borders, but also contribute to figure-ground texture segregation, although requiring substantially more principal components than V4 neurons to reach a 75 % decoding accuracy. Individually, V1/V4 neurons showing larger (negative/positive) figure-ground response differences contribute more to figure-ground segregation. But for V1 neurons, the contribution becomes significant only when many principal components are considered. We conclude that V1 neurons participate in figure-ground segregation primarily by defining the figure borders, and the poorly structured figure-ground information V1 neurons carry could be further utilized by V4 neurons to accomplish figure-ground segregation.

Basolateral amygdala (BLA) is a key hub for affect in the brain,1,2,3 and dysfunction within this area contributes to a host of psychiatric disorders.4,5 BLA is extensively and reciprocally interconnected with frontal cortex,6,7,8,9 and some aspects of its function are evolutionarily conserved across rodents, anthropoid primates, and humans.10 Neuron density in BLA is substantially lower in primates compared to murine rodents,11 and frontal cortex (FC) is dramatically expanded in primates, particularly the more anterior granular and dysgranular areas.12,13,14 Yet, how these anatomical differences influence the projection patterns of single BLA neurons to frontal cortex across rodents and primates is unknown. Using a barcoded connectomic approach, we assessed the single BLA neuron connections to frontal cortex in mice and macaques. We found that BLA neurons are more likely to project to multiple distinct parts of FC in mice than in macaques. Further, while single BLA neuron projections to nucleus accumbens were similarly organized in mice and macaques, BLA-FC connections differed substantially. Notably, BLA connections to subcallosal anterior cingulate cortex (scACC) in macaques were least likely to branch to other medial frontal cortex areas compared to perigenual ACC (pgACC). This pattern of connections was reversed in the mouse homologues of these areas, infralimbic and prelimbic cortex (IL and PL), mirroring functional differences between rodents and non-human primates. Taken together, these results indicate that BLA connections to FC are not linearly scaled from mice to macaques and instead the organization of single-neuron BLA connections is distinct between these species.