Marmoset core visual object recognition behavior is comparable to that of macaques and humans

CalliCog is an open-source cognitive neuroscience toolkit for freely behaving nonhuman primates

Nonhuman primates (NHPs) are pivotal for unlocking the complexities of human cognition, yet traditional cognitive studies remain constrained to specialized laboratories. To address this gap, we present CalliCog: an open-source, scalable in-cage platform tailored for experiments in small freely behaving primate species such as the common marmoset (Callithrix jacchus). CalliCog includes modular operant chambers that operate autonomously and integrate seamlessly with home cages, eliminating human intervention. Our results showcase the power of CalliCog to train experimentally naive marmosets in touchscreen-based cognitive tasks. Across two independent facilities, marmosets achieved touchscreen proficiency within 2 weeks and successfully completed tasks probing behavioral flexibility and working memory. Moreover, CalliCog enabled precise synchronization of behavioral data with electrocorticography (ECoG) recordings from freely moving animals, opening new frontiers for neurobehavioral research. By making CalliCog openly accessible, we aim to democratize cognitive experimentation with small NHPs, narrowing the translational gap between preclinical models and human cognition.

Wild Tibetan Macaques Use a Route-Based Mental Map to Navigate in Large-Scale Space

Many animals face significant challenges in locating and acquiring resources that are unevenly distributed in space and time. In the case of nonhuman primates, it remains unclear how individuals remember goal locations and whether they navigate using a route-based or a coordinate-based mental representation when moving between out-of-sight feeding and resting sites (i.e., large-scale space). Here, we examine spatial memory and mental map formation in wild Tibetan macaques (Macaca thibetana) inhabiting a mountainous, forested ecosystem characterized by steep terrain that limits direct vision to 25 meters. We used an instantaneous scan sampling technique at 10-min intervals to record the behavior and location of macaques on Mt. Huangshan, Anhui Province, China, from September 2020 to August 2023. Over 214 days, we obtained 7180 GPS points of the macaques' locations. Our study revealed that the macaques reused 1264 route segments (average length 204.26 m) at least four times each. The number of feeding and resting sites around the habitual route segment, terrain roughness, and dense vegetation areas significantly influenced the use of route segments by our study group. In addition, we found evidence that the monkeys reused 48 nodes to reorient their travel path. We found that monkeys approached a revisited foraging or resting site from the same limited set of directions, which is inconsistent with a coordinate-based spatial representation. In addition, the direction in which the macaques left a feeding or resting site was significantly different from the straight-line direction required to reach their next feeding or resting site, suggesting that the macaques frequently reoriented their direction of travel to reach their goal. Finally, on average, macaques traveled 24% (CI = 1.24) farther than the straight-line distance to reach revisited feeding and resting sites. From our robust data set, we conclude that Tibetan macaques navigate large spaces using a route-based mental representation that appears to help them locate food resources in dense, rugged montane forests and heterogeneous habitats.

Improving Reproductive Success in Captive Marmosets Through Active Female Choice

The recent upsurge in the use of common marmosets (Callithrix jacchus) as a desirable model for high-priority biomedical research has challenged local and global suppliers struggling to provide sufficient numbers of marmosets for large-scale projects. In laboratories, random male-female pairings are often unsuccessful, with intervals of several months before attempting alternate pairings. Here we address this challenge through a behavioral task that promotes self-directed female selection of potential mates to increase the efficiency of breeding in captive marmosets. We created a partner preference test in which nulliparous females (n = 12) had the opportunity to select between two eligible males (n = 23) at a time, in a forced choice test. In this test, both males and females displayed sexual solicitations. However, the females displayed a clear preference for one male by directing affiliative behaviors toward him including proceptive tongue-flicking, approach, and grooming. Her preference remained consistent across three consecutive test sessions. This method resulted in a 2.5-fold improvement in breeding success within 90 days compared to random pairings. This cost-effective and straightforward pairing practice can be used to enhance breeding efficiency in both small and large marmoset colonies.

Monitoring of nonspatial information within working memory in the common marmoset (Callithrix jacchus)

The mid-dorsolateral prefrontal cortical region (areas 46 and 9/46) is critical for the monitoring of information in working memory both in the macaque monkey brain and the human brain. The presence of this cytoarchitectonic region in the New World marmoset brain was in debate, but recent anatomical evidence demonstrated a limited area 46. This finding raised the question of the extent to which the marmoset brain can support the cognitive control process of monitoring information within working memory. This cognitive control process was assessed in adult marmosets and was shown to be limited to the monitoring of only two items in contrast to macaque monkeys, who can monitor as many as five items in working memory. The results are consistent with the limited development of the relevant prefrontal region in the marmoset and contribute to understanding the evolution of higher cognitive control processes in the primate brain.

Low-cost, portable, easy-to-use kiosks to facilitate home-cage testing of nonhuman primates during vision-based behavioral tasks

Nonhuman primates (NHPs), especially rhesus macaques, have significantly contributed to our understanding of the neural computations underlying human vision. Besides the established homologies in the visual brain areas between these species and our ability to probe detailed neural mechanisms in monkeys at multiple scales, NHPs' ability to perform human-like visual behavior makes them an extremely appealing animal model of human vision. Traditionally, such behavioral studies have been conducted in controlled laboratory settings, offering experimenters tight control over variables like luminance, eye movements, and auditory interference. However, in-lab experiments have several constraints, including limited experimental time, the need for dedicated human experimenters, additional lab space requirements, invasive surgeries for headpost implants, and extra time and training for chairing and head restraints. To overcome these limitations, we propose adopting home-cage behavioral training and testing of NHPs, enabling the administration of many vision-based behavioral tasks simultaneously across multiple monkeys with reduced human personnel requirements, no NHP head restraint, and monkeys' unrestricted access to experiments. In this article, we present a portable, low-cost, easy-to-use kiosk system developed to conduct home-cage vision-based behavioral tasks in NHPs. We provide details of its operation and build to enable more open-source development of this technology. Furthermore, we present validation results using behavioral measurements performed in the lab and in NHP home cages, demonstrating the system's reliability and potential to enhance the efficiency and flexibility of NHP behavioral research.NEW & NOTEWORTHY Training nonhuman primates (NHPs) for vision-based behavioral tasks in a laboratory setting is a time-consuming process and comes with many limitations. To overcome these challenges, we have developed an affordable, open-source, wireless, touchscreen training system that can be placed in the NHPs' housing environment. This system enables NHPs to work at their own pace. It provides a platform to implement continuous behavioral training protocols without major experimenter intervention and eliminates the need for other standard practices like NHP chair training, collar placement, and head restraints. Hence, these kiosks ultimately contribute to animal welfare and therefore better-quality neuroscience in the long run. In addition, NHPs quickly learn complex behavioral tasks using this system, making it a promising tool for wireless electrophysiological research in naturalistic, unrestricted environments to probe the relation between brain and behavior.

Parallel patterns of cognitive aging in marmosets and macaques

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.

Improving reproductive success in captive marmosets through active female choice

The recent upsurge in the use of common marmosets (Callithrix jacchus) as a desirable model for high priority biomedical research has challenged local and global suppliers struggling to provide sufficient numbers of marmosets for large scale projects. Scientific research laboratories are increasingly establishing institutional breeding colonies, in part to combat the resulting shortage and high cost of commercially available animals, and in part to have maximum control over research lines involving reproduction and development. For such laboratories, efficient marmoset breeding can be challenging and time consuming. Random male/female pairings are often unsuccessful, with intervals of several months before attempting alternate pairings. Here we address this challenge through a behavioral task that promotes self-directed female selection of potential mates to increase the efficiency of breeding in captive marmosets. We created a partner preference test ('love maze') in which nulliparous females (n=12) had the opportunity to select between two eligible males (n=23) at a time, in a forced choice test. In this test, both males usually displayed sexual solicitations. However, the female would clearly indicate her preference for one. Most commonly, the female actively ignored the non-preferred male and directed overt prosocial behaviors (e.g. proceptive tongue-flicking, approach and grooming) to the preferred male. Moreover, once a male was selected in this context, the female would continue to prefer him over other males in three consecutive testing sessions. Compared with random pairings, this directed female choice showed a 2.5-fold improvement in breeding within 90 days compared to random pairings. This cost-effective and straightforward pairing practice can be used to enhance breeding efficiency in both small and large marmoset colonies.

Acute Neuropixels Recordings in the Marmoset Monkey

High-density linear probes, such as Neuropixels, provide an unprecedented opportunity to understand how neural populations within specific laminar compartments contribute to behavior. Marmoset monkeys, unlike macaque monkeys, have a lissencephalic (smooth) cortex that enables recording perpendicular to the cortical surface, thus making them an ideal animal model for studying laminar computations. Here we present a method for acute Neuropixels recordings in the common marmoset (Callithrix jacchus). The approach replaces the native dura with an artificial silicon-based dura that grants visual access to the cortical surface, which is helpful in avoiding blood vessels, ensures perpendicular penetrations, and could be used in conjunction with optical imaging or optogenetic techniques. The chamber housing the artificial dura is simple to maintain with minimal risk of infection and could be combined with semichronic microdrives and wireless recording hardware. This technique enables repeated acute penetrations over a period of several months. With occasional removal of tissue growth on the pial surface, recordings can be performed for a year or more. The approach is fully compatible with Neuropixels probes, enabling the recording of hundreds of single neurons distributed throughout the cortical column.

Acute Neuropixels recordings in the marmoset monkey

High-density linear probes, like Neuropixels, provide an unprecedented opportunity to understand how neural populations within specific laminar compartments contribute to behavior. Marmoset monkeys, unlike macaque monkeys, have a lissencephalic (smooth) cortex that enables recording perpendicular to the cortical surface, thus making them an ideal animal model for studying laminar computations. Here we present a method for acute Neuropixels recordings in the common marmoset (Callithrix jacchus). The approach replaces the native dura with an artificial silicon-based dura that grants visual access to the cortical surface, which is helpful in avoiding blood vessels, ensures perpendicular penetrations, and could be used in conjunction with optical imaging or optogenetic techniques. The chamber housing the artificial dura is simple to maintain with minimal risk of infection and could be combined with semi-chronic microdrives and wireless recording hardware. This technique enables repeated acute penetrations over a period of several months. With occasional removal of tissue growth on the pial surface, recordings can be performed for a year or more. The approach is fully compatible with Neuropixels probes, enabling the recording of hundreds of single neurons distributed throughout the cortical column.