Primacy of vision shapes behavioral strategies and neural substrates of spatial navigation in marmoset hippocampus

The role of the hippocampus in spatial navigation has been primarily studied in nocturnal mammals, such as rats, that lack many adaptations for daylight vision. Here we demonstrate that during 3D navigation, the common marmoset, a new world primate adapted to daylight, predominantly uses rapid head-gaze shifts for visual exploration while remaining stationary. During active locomotion marmosets stabilize the head, in contrast to rats that use low-velocity head movements to scan the environment as they locomote. Pyramidal neurons in the marmoset hippocampus CA3/CA1 regions predominantly show mixed selectivity for 3D spatial view, head direction, and place. Exclusive place selectivity is scarce. Inhibitory interneurons are predominantly mixed selective for angular head velocity and translation speed. Finally, we found theta phase resetting of local field potential oscillations triggered by head-gaze shifts. Our findings indicate that marmosets adapted to their daylight ecological niche by modifying exploration/navigation strategies and their corresponding hippocampal specializations.

Distributed representations of prediction error signals across the cortical hierarchy are synergistic

A relevant question concerning inter-areal communication in the cortex is whether these interactions are synergistic. Synergy refers to the complementary effect of multiple brain signals conveying more information than the sum of each isolated signal. Redundancy, on the other hand, refers to the common information shared between brain signals. Here, we dissociated cortical interactions encoding complementary information (synergy) from those sharing common information (redundancy) during prediction error (PE) processing. We analyzed auditory and frontal electrocorticography (ECoG) signals in five common awake marmosets performing two distinct auditory oddball tasks and investigated to what extent event-related potentials (ERP) and broadband (BB) dynamics encoded synergistic and redundant information about PE processing. The information conveyed by ERPs and BB signals was synergistic even at lower stages of the hierarchy in the auditory cortex and between auditory and frontal regions. Using a brain-constrained neural network, we simulated the synergy and redundancy observed in the experimental results and demonstrated that the emergence of synergy between auditory and frontal regions requires the presence of strong, long-distance, feedback, and feedforward connections. These results indicate that distributed representations of PE signals across the cortical hierarchy can be highly synergistic.

Multiple processes of vocal sensory-motor interaction in primate auditory cortex

Sensory-motor interactions in the auditory system play an important role in vocal self-monitoring and control. These result from top-down corollary discharges, relaying predictions about vocal timing and acoustics. Recent evidence suggests such signals may be two distinct processes, one suppressing neural activity during vocalization and another enhancing sensitivity to sensory feedback, rather than a single mechanism. Single-neuron recordings have been unable to disambiguate due to overlap of motor signals with sensory inputs. Here, we sought to disentangle these processes in marmoset auditory cortex during production of multi-phrased 'twitter' vocalizations. Temporal responses revealed two timescales of vocal suppression: temporally-precise phasic suppression during phrases and sustained tonic suppression. Both components were present within individual neurons, however, phasic suppression presented broadly regardless of frequency tuning (gating), while tonic was selective for vocal frequencies and feedback (prediction). This suggests that auditory cortex is modulated by concurrent corollary discharges during vocalization, with different computational mechanisms.

Cortisol levels across the lifespan in common marmosets (Callithrix jacchus)

Human aging is associated with senescence of the hypothalamic-pituitary-adrenal (HPA) axis, leading to progressive dysregulation characterized by increased cortisol exposure. This key hormone is implicated in the pathogenesis of many age-related diseases. Common marmosets (Callithrix jacchus) display a wide spectrum of naturally occurring age-related pathologies that compare similarly to humans and are increasingly used as translational models of aging and age-related disease. Whether the marmoset HPA axis also shows senescence with increasing age is unknown. We analyzed hair cortisol concentration (HCC) across the lifespan of 50 captive common marmosets, ranging in age from approximately 2 months-14.5 years, via a cross-sectional design. Samples were processed and analyzed for cortisol using enzyme immunoassay. HCC ranged from 1416 to 15,343 pg/mg and was negatively correlated with age. We found significant main effects of age group (infant, adolescent, adult, aged, very aged) and sex on HCC, and no interaction effects. Infants had significantly higher levels of HCC compared with all other age groups. Females had higher HCC than males. There was no interaction between age and sex. These results suggest marmosets do not show dysregulation of the HPA axis with increasing age, as measured via HCC.

Mapping of facial and vocal processing in common marmosets with ultra-high field fMRI

Primate communication relies on multimodal cues, such as vision and audition, to facilitate the exchange of intentions, enable social interactions, avoid predators, and foster group cohesion during daily activities. Understanding the integration of facial and vocal signals is pivotal to comprehend social interaction. In this study, we acquire whole-brain ultra-high field (9.4 T) fMRI data from awake marmosets (Callithrix jacchus) to explore brain responses to unimodal and combined facial and vocal stimuli. Our findings reveal that the multisensory condition not only intensifies activations in the occipito-temporal face patches and auditory voice patches but also engages a more extensive network that includes additional parietal, prefrontal and cingulate areas, compared to the summed responses of the unimodal conditions. By uncovering the neural network underlying multisensory audiovisual integration in marmosets, this study highlights the efficiency and adaptability of the marmoset brain in processing facial and vocal social signals, providing significant insights into primate social communication.

Nerve sheath tumor in the forearm of a common marmoset (Callithrix jacchus)

Tumors of the skin and subcutaneous tissues are uncommon in marmosets. In this report, we describe the gross, histopathology, and immunohistochemical findings of a nerve sheath tumor that arose in the left forearm of an adult female marmoset (Callthrix jacchus).

Early parental deprivation during primate infancy has a lifelong impact on gene expression in the male marmoset brain

Adverse early life experiences are well-established risk factors for neurological disorders later in life. However, the molecular mechanisms underlying the impact of adverse experiences on neurophysiological systems throughout life remain incompletely understood. Previous studies suggest that social attachment to parents in early development are indispensable for infants to grow into healthy adults. In situations where multiple offspring are born in a single birth in common marmosets, human hand-rearing is employed to ensure the survival of the offspring in captivity. However, hand-reared marmosets often exhibit behavioral abnormalities, including abnormal vocalizations, excessive attachment to the caretaker, and aggressive behavior. In this study, comprehensive transcriptome analyses were conducted on hippocampus tissues, a neuroanatomical region sensitive to social attachment, obtained from human hand-reared (N = 6) and parent-reared male marmosets (N = 5) at distinct developmental stages. Our analyses revealed consistent alterations in a subset of genes, including those related to neurodevelopmental diseases, across different developmental stages, indicating their continuous susceptibility to the effects of early parental deprivation. These findings highlight the dynamic nature of gene expression in response to early life experiences and suggest that the impact of early parental deprivation on gene expression may vary across different stages of development.

In vivo functional brain mapping using ultra-high-field fMRI in awake common marmosets

The common marmoset (Callithrix jacchus) is gaining attention in the field of cognitive neuroscience. The development of an effective protocol for fMRI data acquisition in awake marmosets is a key factor in developing reliable comparative studies. Here, we describe a protocol to obtain fMRI data in awake marmosets using auditory and visual stimulation. We describe steps for surgical and anesthesia procedures, MRI training, and positioning the marmosets within an MRI-compatible body restraint. We then detail fMRI scanning and preprocessing of functional images. For complete details on the use and execution of this protocol, please refer to Jafari et al. (2023).1.

Encoding identity in the marmoset

Hippocampal cells integrate multisensory input to represent the identity of others.

Cross-modal representation of identity in the primate hippocampus

Faces and voices are the dominant social signals used to recognize individuals among primates. Yet, it is not known how these signals are integrated into a cross-modal representation of individual identity in the primate brain. We discovered that, although single neurons in the marmoset hippocampus exhibited selective responses when presented with the face or voice of a specific individual, a parallel mechanism for representing the cross-modal identities for multiple individuals was evident within single neurons and at the population level. Manifold projections likewise showed the separability of individuals as well as clustering for others' families, which suggests that multiple learned social categories are encoded as related dimensions of identity in the hippocampus. Neural representations of identity in the hippocampus are thus both modality independent and reflect the primate social network.

Frontal cortex activity during the production of diverse social communication calls in marmoset monkeys

Vocal communication is essential for social behaviors in humans and non-human primates. While the frontal cortex is crucial to human speech production, its role in vocal production in non-human primates has long been questioned. It is unclear whether activities in the frontal cortex represent diverse vocal signals used in non-human primate communication. Here we studied single neuron activities and local field potentials (LFP) in the frontal cortex of male marmoset monkeys while the animal engaged in vocal exchanges with conspecifics in a social environment. We found that both single neuron activities and LFP were modulated by the production of each of the four major call types. Moreover, neural activities showed distinct patterns for different call types and theta-band LFP oscillations showed phase-locking to the phrases of twitter calls, suggesting a neural representation of vocalization features. Our results suggest important functions of the marmoset frontal cortex in supporting the production of diverse vocalizations in communication.

Effects of Cortical Stimulation on Feedback-Dependent Vocal Control in Non-Human Primates

OBJECTIVES

Hearing plays an important role in our ability to control voice, and perturbations in auditory feedback result in compensatory changes in vocal production. The auditory cortex (AC) has been proposed as an important mediator of this behavior, but causal evidence is lacking. We tested this in an animal model, hypothesizing that AC is necessary for vocal self-monitoring and feedback-dependent control, and that altering activity in AC during vocalization will interfere with vocal control.

METHODS

We implanted two marmoset monkeys (Callithrix jacchus) with bilateral AC electrode arrays. Acoustic signals were recorded from vocalizing marmosets while altering vocal feedback or electrically stimulating AC during random subsets of vocalizations. Feedback was altered by real-time frequency shifts and presented through headphones and electrical stimulation delivered to individual electrodes. We analyzed recordings to measure changes in vocal acoustics during shifted feedback and stimulation, and to determine their interaction. Results were correlated with the location and frequency tuning of stimulation sites.

RESULTS

Consistent with previous results, we found electrical stimulation alone evoked changes in vocal production. Results were stronger in the right hemisphere, but decreased with lower currents or repeated stimulation. Simultaneous stimulation and shifted feedback significantly altered vocal control for a subset of sites, decreasing feedback compensation at some and increasing it at others. Inhibited compensation was more likely at sites closer to vocal frequencies.

CONCLUSIONS

Results provide causal evidence that the AC is involved in feedback-dependent vocal control, and that it is sufficient and may also be necessary to drive changes in vocal production.

LEVEL OF EVIDENCE

N/A Laryngoscope, 133:1-10, 2023.

Delay-related activity in marmoset prefrontal cortex

Persistent delay-period activity in prefrontal cortex (PFC) has long been regarded as a neural signature of working memory (WM). Electrophysiological investigations in macaque PFC have provided much insight into WM mechanisms; however, a barrier to understanding is the fact that a portion of PFC lies buried within the principal sulcus in this species and is inaccessible for laminar electrophysiology or optical imaging. The relatively lissencephalic cortex of the New World common marmoset (Callithrix jacchus) circumvents such limitations. It remains unknown, however, whether marmoset PFC neurons exhibit persistent activity. Here, we addressed this gap by conducting wireless electrophysiological recordings in PFC of marmosets performing a delayed-match-to-location task on a home cage-based touchscreen system. As in macaques, marmoset PFC neurons exhibited sample-, delay-, and response-related activity that was directionally tuned and linked to correct task performance. Models constructed from population activity consistently and accurately predicted stimulus location throughout the delay period, supporting a framework of delay activity in which mnemonic representations are relatively stable in time. Taken together, our findings support the existence of common neural mechanisms underlying WM performance in PFC of macaques and marmosets and thus validate the marmoset as a suitable model animal for investigating the microcircuitry underlying WM.

Sound localization acuity of the common marmoset (Callithrix jacchus)

The common marmoset (Callithrix jacchus) is a small arboreal New World primate which has emerged as a promising model in auditory neuroscience. One potentially useful application of this model system is in the study of the neural mechanism underlying spatial hearing in primate species, as the marmosets need to localize sounds to orient their head to events of interest and identify their vocalizing conspecifics that are not visible. However, interpretation of neurophysiological data on sound localization requires an understanding of perceptual abilities, and the sound localization behavior of marmosets has not been well studied. The present experiment measured sound localization acuity using an operant conditioning procedure in which marmosets were trained to discriminate changes in sound location in the horizontal (azimuth) or vertical (elevation) dimension. Our results showed that the minimum audible angle (MAA) for horizontal and vertical discrimination was 13.17° and 12.53°, respectively, for 2 to 32 kHz Gaussian noise. Removing the monaural spectral cues tended to increase the horizontal localization acuity (11.31°). Marmosets have larger horizontal MAA (15.54°) in the rear than the front. Removing the high-frequency (> 26 kHz) region of the head-related transfer function (HRTF) affected vertical acuity mildly (15.76°), but removing the first notch (12-26 kHz) region of HRTF substantially reduced the vertical acuity (89.01°). In summary, our findings indicate that marmosets' spatial acuity is on par with other species of similar head size and field of best vision, and they do not appear to use monaural spectral cues for horizontal discrimination but rely heavily on first notch region of HRTF for vertical discrimination.

Multi-area recordings and optogenetics in the awake, behaving marmoset

The common marmoset has emerged as a key model in neuroscience. Marmosets are small in size, show great potential for genetic modification and exhibit complex behaviors. Thus, it is necessary to develop technology that enables monitoring and manipulation of the underlying neural circuits. Here, we describe a novel approach to record and optogenetically manipulate neural activity in awake, behaving marmosets. Our design utilizes a light-weight, 3D printed titanium chamber that can house several high-density silicon probes for semi-chronic recordings, while enabling simultaneous optogenetic stimulation. We demonstrate the application of our method in male marmosets by recording multi- and single-unit data from areas V1 and V6 with 192 channels simultaneously, and show that optogenetic activation of excitatory neurons in area V6 can influence behavior in a detection task. This method may enable future studies to investigate the neural basis of perception and behavior in the marmoset.

Acclimatizing and training freely viewing marmosets for behavioral and electrophysiological experiments in oculomotor tasks

The marmoset is a small-bodied primate with behavioral capacities and brain structures comparable to macaque monkeys and humans. Its amenability to modern biotechnological techniques like optogenetics, chemogenetics, and generation of transgenic primates have attracted neuroscientists' attention to use it as a model in neuroscience. In the past decade, several laboratories have been developing and refining tools and techniques for performing behavioral and electrophysiological experiments in this new model. In this regard, we developed a protocol to acclimate the marmoset to sit calmly in a primate chair; a method to calibrate the eye-tracking system while marmosets were freely viewing the screen; and a procedure to map motor field of neurons in the SC in freely viewing marmosets. Using a squeeze-walled transfer box, the animals were acclimatized, and chair trained in less than 4 weeks, much shorter than what other studies reported. Using salient stimuli allowed quick and accurate calibration of the eye-tracking system in untrained freely viewing marmosets. Applying reverse correlation to spiking activity and saccadic eye movements, we were able to map motor field of SC neurons in freely viewing marmosets. These refinements shortened the acclimation period, most likely reduced stress to the subjects, and allowed more efficient eye calibration and motor field mapping in freely viewing marmosets. With a penetration angle of 38 degrees, all 16 channels of the electrode array, that is, all recorded neurons across SC layers, had overlapping visual receptive and motor fields, indicating perpendicular penetration to the SC.

Potential trade-off between olfactory and visual discrimination learning in common marmosets (Callithrix jacchus): Implications for the assessment of age-related cognitive decline

Olfactory dysfunction has been identified as an early biomarker for dementia risk but has rarely been assessed in nonhuman primate models of human aging. To better characterize common marmosets as such models, we assessed olfactory discrimination performance in a sample of 10 animals (5 females), aged 2.5-8.9 years old. The monkeys were proficient in the discrimination and reversal of visual stimuli but naïve to odor stimuli. For olfactory discrimination, the monkeys performed a series of six discriminations of increasing difficulty between two odor stimuli. We found no evidence for an age-related decline as both young and older individuals were able to perform the discriminations in roughly the same number of trials. In addition, the older monkeys had faster responses than the younger animals. However, we noted that when adjusted for age, the speed of acquisition of the first discrimination in the olfactory modality was inversely correlated to the speed of acquisition of their first discrimination of two visual stimuli months earlier. These results suggest that marmosets may compensate for sensory deficits in one modality with higher sensory performance in another. These data have broad implications for the assessment of age-related cognitive decline and the categorization of animals as impaired or nonimpaired.

A prosocial function of head-gaze aversion and head-cocking in common marmosets

Gaze aversion is a behavior adopted by several mammalian and non-mammalian species in response to eye contact, and is usually interpreted as a reaction to a perceived threat. Unlike many other primate species, common marmosets (Callithrix jacchus) are thought to have a high tolerance for direct gaze, barely exhibiting gaze avoidance towards conspecifics and humans. Here we show that this does not hold for marmosets interacting with a familiar experimenter who suddenly establishes eye contact in a playful interaction (peekaboo). Video footage synchronously recorded from the perspective of the marmoset and the experimenter showed that the monkeys consistently alternated between eye contact and head-gaze aversion, and that these responses were often preceded by head-cocking. We hypothesize that this behavioral strategy helps marmosets to temporarily disengage from emotionally overwhelming social stimulation due to sight of another individual's face, in order to prepare for a new round of affiliative face-to-face interactions.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.

Robust locomotor performance of squirrel monkeys (Saimiri boliviensis) in response to simulated changes in support diameter and compliance

Arboreal environments require overcoming navigational challenges not typically encountered in other terrestrial habitats. Supports are unevenly distributed and vary in diameter, orientation, and compliance. To better understand the strategies that arboreal animals use to maintain stability in this environment, laboratory researchers must endeavor to mimic those conditions. Here, we evaluate how squirrel monkeys (Saimiri boliviensis) adjust their locomotor mechanics in response to variation in support diameter and compliance. We used high-speed cameras to film two juvenile female monkeys as they walked across poles of varying diameters (5, 2.5, and 1.25 cm). Poles were mounted on either a stiff wooden base ("stable" condition) or foam blocks ("compliant" condition). Six force transducers embedded within the pole trackway recorded substrate reaction forces during locomotion. We predicted that squirrel monkeys would walk more slowly on narrow and compliant supports and adopt more "compliant" gait mechanics, increasing stride lengths, duty factors, and an average number of limbs gripping the support, while the decreasing center of mass height, stride frequencies, and peak forces. We observed few significant adjustments to squirrel monkey locomotor kinematics in response to changes in either support diameter or compliance, and the changes we did observe were often tempered by interactions with locomotor speed. These results differ from a similar study of common marmosets (i.e., Callithrix jacchus, with relatively poor grasping abilities), where variation in diameter and compliance substantially impacted gait kinematics. Squirrel monkeys' strong grasping apparatus, long and mobile tails, and other adaptations for arboreal travel likely facilitate robust locomotor performance despite substrate precarity.

Motivational increase of androgens and behavior by infant distress calls in highly responsive common marmoset fathers, Callithrix jacchus

Common marmoset fathers are highly involved in care of their infants. However, variability exists in their response to infant behavior even in paternally experienced fathers. Using infant distress cries as a motivation test, we investigated: 1. the differences in paternally experienced fathers' motivation to search for the infant vocalization stimuli; 2. the relationship between a father's motivation to search for the source of the infant cries and testosterone levels; and 3. if there is a rapid steroidogenesis pathway leading to increased testosterone and estradiol in the peripheral circulation. Only 44% of the paternally experienced fathers showed a high frequency of searching for the source of the infant distress cries. Through the use of multisteroid analysis, we found high responsive fathers had significantly higher levels of progesterone and testosterone in response to infant distress cries compared to a control stimulus with progesterone and androstenedione correlating with testosterone, while no differences were seen in low responders. The frequency to search for the infant stimuli was positively correlated with higher testosterone compared to control vocal levels. These results suggest that searching for the source of infant cries represents a motivation behavior for fathers that is activated by testosterone and reflects rapid circulating testosterone.

Fatal Human Alphaherpesvirus 1 Infection in Free-Ranging Black-Tufted Marmosets in Anthropized Environments, Brazil, 2012–2019

Human alphaherpesvirus 1 (HuAHV1) causes fatal neurologic infections in captive New World primates. To determine risks for interspecies transmission, we examined data for 13 free-ranging, black-tufted marmosets (Callithrix penicillata) that died of HuAHV1 infection and had been in close contact with humans in anthropized areas in Brazil during 2012–2019. We evaluated pathologic changes in the marmosets, localized virus and antigen, and assessed epidemiologic features. The main clinical findings were neurologic signs, necrotizing meningoencephalitis, and ulcerative glossitis; 1 animal had necrotizing hepatitis. Transmission electron microscopy revealed intranuclear herpetic inclusions, and immunostaining revealed HuAHV1 and herpesvirus particles in neurons, glial cells, tongue mucosal epithelium, and hepatocytes. PCR confirmed HuAHV1 infection. These findings illustrate how disruption of the One Health equilibrium in anthropized environments poses risks for interspecies virus transmission with potential spillover not only from animals to humans but also from humans to free-ranging nonhuman primates or other animals.

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.

An open-source tool for automated analysis of breathing behaviors in common marmosets and rodents

The respiratory system maintains homeostatic levels of oxygen (O2) and carbon dioxide (CO2) in the body through rapid and efficient regulation of breathing frequency and depth (tidal volume). The commonly used methods of analyzing breathing data in behaving experimental animals are usually subjective, laborious, and time-consuming. To overcome these hurdles, we optimized an analysis toolkit for the unsupervised study of respiratory activities in animal subjects. Using this tool, we analyzed breathing behaviors of the common marmoset (Callithrix jacchus), a New World non-human primate model. Using whole-body plethysmography in room air as well as acute hypoxic (10% O2) and hypercapnic (6% CO2) conditions, we describe breathing behaviors in awake, freely behaving marmosets. Our data indicate that marmosets' exposure to acute hypoxia decreased metabolic rate and increased sigh rate. However, the hypoxic condition did not augment ventilation. Hypercapnia, on the other hand, increased both the frequency and depth (i.e., tidal volume) of breathing.

Fast and accurate annotation of acoustic signals with deep neural networks

Acoustic signals serve communication within and across species throughout the animal kingdom. Studying the genetics, evolution, and neurobiology of acoustic communication requires annotating acoustic signals: segmenting and identifying individual acoustic elements like syllables or sound pulses. To be useful, annotations need to be accurate, robust to noise, and fast.

We here introduce DeepAudioSegmenter (DAS), a method that annotates acoustic signals across species based on a deep-learning derived hierarchical presentation of sound. We demonstrate the accuracy, robustness, and speed of DAS using acoustic signals with diverse characteristics from insects, birds, and mammals. DAS comes with a graphical user interface for annotating song, training the network, and for generating and proofreading annotations. The method can be trained to annotate signals from new species with little manual annotation and can be combined with unsupervised methods to discover novel signal types. DAS annotates song with high throughput and low latency for experimental interventions in realtime. Overall, DAS is a universal, versatile, and accessible tool for annotating acoustic communication signals.

Personality, subjective well-being, and the serotonin 1a receptor gene in common marmosets (Callithrix jacchus)

Studies of personality traits in common marmosets (Callithrix jacchus) indicate that there are five or six constructs-Sociability, Dominance, Neuroticism, Openness, and two related to Conscientiousness. The present study attempted to determine whether our earlier study of laboratory-housed individuals only yielded three-Dominance, Sociability, and Neuroticism-because of a low amount of between-subjects variance. To do so, we increased our sample size from 77 to 128. In addition, we ascertained the reliability and validity of ratings and whether polymorphisms related to the serotonin 1a receptor were associated with personality. We found Sociability, Dominance, and Negative Affect factors that resembled three domains found in previous studies, including ours. We also found an Openness and Impulsiveness factor, the latter of which bore some resemblance to Conscientiousness, and two higher-order factors, Pro-sociality and Boldness. In further analyses, we could not exclude the possibility that Pro-sociality and Boldness represented a higher-level of personality organization. Correlations between personality factors and well-being were consistent with the definitions of the factors. There were no significant associations between personality and genotype. These results suggest that common marmoset personality structure varies as a function of rearing or housing variables that have not yet been investigated systematically.

Comparative computer-assisted sperm analysis in non-human primates

BACKGROUND

Biomedical research has recently focused on developing new models of human disease by implementing genome-editing strategies in non-human primates (NHPs) to introduce relevant gene mutations. There is a need to establish objective semen evaluation methods to select sires for in vitro fertilization to perform germline editing in embryos.

METHODS

Sperm motility kinematic parameters were evaluated using a computer-assisted semen analysis (CASA) instrument for rhesus macaques (Macaca mulatta), cynomolgus macaques (Macaca fascicularis), and common marmosets (Callithrix jacchus).

RESULTS

Normative sperm kinematic parameters were established, revealing differences between marmosets and macaques. The impact of season on rhesus macaque sperm motility was modest, where changes in sperm motility related to season were dependent on the individual male.

CONCLUSIONS

These data provide a baseline of normative kinematic parameters for three captive NHP species, in which implementation of CASA may serve as a tool to evaluate NHP semen quality.

Neural network of social interaction observation in marmosets

A crucial component of social cognition is to observe and understand the social interactions of other individuals. A promising nonhuman primate model for investigating the neural basis of social interaction observation is the common marmoset (Callithrix jacchus), a small New World primate that shares a rich social repertoire with humans. Here, we used functional magnetic resonance imaging acquired at 9.4 T to map the brain areas activated by social interaction observation in awake marmosets. We discovered a network of subcortical and cortical areas, predominately in the anterior lateral frontal and medial frontal cortex, that was specifically activated by social interaction observation. This network resembled that recently identified in Old World macaque monkeys. Our findings suggest that this network is largely conserved between New and Old World primates and support the use of marmosets for studying the neural basis of social cognition.

Higher social tolerance in wild versus captive common marmosets: the role of interdependence

Social tolerance in a group reflects the balance between within-group competition and interdependence: whereas increased competition leads to a reduction in social tolerance, increased interdependence increases it. Captivity reduces both feeding competition and interdependence and can therefore affect social tolerance. In independently breeding primates, social tolerance has been shown to be higher in captivity, indicating a strong effect of food abundance. It is not known, however, how social tolerance in cooperative breeders, with their much higher interdependence, responds to captivity. Here, we therefore compared social tolerance between free-ranging and captive groups in the cooperatively breeding common marmoset and found higher social tolerance (measured as proximity near food, co-feeding, and food sharing) in the wild. Most likely, social tolerance in the wild is higher because interdependence is particularly high in the wild, especially because infant care is more costly there than in captivity. These results indicate that the high social tolerance of these cooperative breeders in captivity is not an artefact, and that captive data may even have underestimated it. They may also imply that the cooperative breeding and foraging of our hominin ancestors, which relied on strong interdependence at multiple levels, was associated with high social tolerance.

The role of adaptation in generating monotonic rate codes in auditory cortex

In primary auditory cortex, slowly repeated acoustic events are represented temporally by the stimulus-locked activity of single neurons. Single-unit studies in awake marmosets (Callithrix jacchus) have shown that a sub-population of these neurons also monotonically increase or decrease their average discharge rate during stimulus presentation for higher repetition rates. Building on a computational single-neuron model that generates stimulus-locked responses with stimulus evoked excitation followed by strong inhibition, we find that stimulus-evoked short-term depression is sufficient to produce synchronized monotonic positive and negative responses to slowly repeated stimuli. By exploring model robustness and comparing it to other models for adaptation to such stimuli, we conclude that short-term depression best explains our observations in single-unit recordings in awake marmosets. Together, our results show how a simple biophysical mechanism in single neurons can generate complementary neural codes for acoustic stimuli.

Towards a new taxonomy of primate vocal production learning

The extent to which vocal learning can be found in nonhuman primates is key to reconstructing the evolution of speech. Regarding the adjustment of vocal output in relation to auditory experience (vocal production learning in the narrow sense), effects on the ontogenetic trajectory of vocal development as well as adjustment to group-specific call features have been found. Yet, a comparison of the vocalizations of different primate genera revealed striking similarities in the structure of calls and repertoires in different species of the same genus, indicating that the structure of nonhuman primate vocalizations is highly conserved. Thus, modifications in relation to experience only appear to be possible within relatively tight species-specific constraints. By contrast, comprehension learning may be extremely rapid and open-ended. In conjunction, these findings corroborate the idea of an ancestral independence of vocal production and auditory comprehension learning. To overcome the futile debate about whether or not vocal production learning can be found in nonhuman primates, we suggest putting the focus on the different mechanisms that may mediate the adjustment of vocal output in response to experience; these mechanisms may include auditory facilitation and learning from success. This article is part of the theme issue 'What can animal communication teach us about human language?'

Spatial encoding in primate hippocampus during free navigation

The hippocampus comprises two neural signals-place cells and θ oscillations-that contribute to facets of spatial navigation. Although their complementary relationship has been well established in rodents, their respective contributions in the primate brain during free navigation remains unclear. Here, we recorded neural activity in the hippocampus of freely moving marmosets as they naturally explored a spatial environment to more explicitly investigate this issue. We report place cells in marmoset hippocampus during free navigation that exhibit remarkable parallels to analogous neurons in other mammalian species. Although θ oscillations were prevalent in the marmoset hippocampus, the patterns of activity were notably different than in other taxa. This local field potential oscillation occurred in short bouts (approximately .4 s)-rather than continuously-and was neither significantly modulated by locomotion nor consistently coupled to place-cell activity. These findings suggest that the relationship between place-cell activity and θ oscillations in primate hippocampus during free navigation differs substantially from rodents and paint an intriguing comparative picture regarding the neural basis of spatial navigation across mammals.

Vocal state change through laryngeal development

Across vertebrates, progressive changes in vocal behavior during postnatal development are typically attributed solely to developing neural circuits. How the changing body influences vocal development remains unknown. Here we show that state changes in the contact vocalizations of infant marmoset monkeys, which transition from noisy, low frequency cries to tonal, higher pitched vocalizations in adults, are caused partially by laryngeal development. Combining analyses of natural vocalizations, motorized excised larynx experiments, tensile material tests and high-speed imaging, we show that vocal state transition occurs via a sound source switch from vocal folds to apical vocal membranes, producing louder vocalizations with higher efficiency. We show with an empirically based model of descending motor control how neural circuits could interact with changing laryngeal dynamics, leading to adaptive vocal development. Our results emphasize the importance of embodied approaches to vocal development, where exploiting biomechanical consequences of changing material properties can simplify motor control, reducing the computational load on the developing brain.

Critique of Pure Marmoset

The common marmoset, a New World (platyrrhine) monkey, is currently being fast-tracked as a non-human primate model species, especially for genetic modification but also as a general-purpose model for research on the brain and behavior bearing on the human condition. Compared to the currently dominant primate model, the catarrhine macaque monkey, marmosets are notable for certain evolutionary specializations, including their propensity for twin births, their very small size (a result of phyletic dwarfism), and features related to their small size (rapid development and relatively short lifespan), which result in these animals yielding experimental results more rapidly and at lower cost. Macaques, however, have their own advantages. Importantly, macaques are more closely related to humans (which are also catarrhine primates) than are marmosets, sharing approximately 20 million more years of common descent, and are demonstrably more similar to humans in a variety of genomic, molecular, and neurobiological characteristics. Furthermore, the very specializations of marmosets that make them attractive as experimental subjects, such as their rapid development and short lifespan, are ways in which marmosets differ from humans and in which macaques more closely resemble humans. These facts warrant careful consideration of the trade-offs between convenience and cost, on the one hand, and biological realism, on the other, in choosing between non-human primate models of human biology. Notwithstanding the advantages marmosets offer as models, prudence requires continued commitment to research on macaques and other primate species.

Cross-sectional comparison of health-span phenotypes in young versus geriatric marmosets

The development of the marmoset as a translational model for healthspan and lifespan studies relies on the characterization of health parameters in young and geriatric marmosets. This cross-sectional study examined health phenotypes in marmosets for five domains of interest for human health and aging: mobility, cognition, metabolism, homeostasis, and immune function. Geriatric marmosets were found to have significant executive function impairment when compared to young animals. While geriatric animals did not show gross abnormalities in mobility and measures of locomotion, their types of movement were altered from young animals. Geriatric marmosets had alterations in cardiac function, with significantly increased mean arterial pressures; metabolism, with significantly lower VO2 ; and suppressed immune function. Further, this study sought to characterize and describe histopathology for both young and geriatric healthy marmosets. Overall this study provides a characterization of health parameters for young and geriatric marmosets which will greatly enhance future aging and interventional testing in marmosets.

Sibling sex, but not androgens, shapes phenotypes in perinatal common marmosets (Callithrix jacchus)

When offspring share a womb, interactions among fetuses can impart lasting impressions on phenotypic outcomes. Such intrauterine interactions often are mediated by sex steroids (estrogens and androgens) produced by the developing fetuses. In many mammals, intrauterine interactions between brothers and sisters lead to masculinization of females, which can induce fitness consequences. Many litter-bearing primates, though, seem to escape androgen-mediated litter effects, begging why? Here, we investigated how the sex composition (i.e., same- or mixed-sex) of litters influences perinatal outcomes in the common marmoset monkey (Callithrix jacchus), using a combination of physiological, morphological, and behavioural assays. We hypothesized that androgens from male fetuses would mediate developmental differences across litter types. We found that newborns (24-36 hours old) from same- and mixed-sex litters were indistinguishable by urinary androgen profiles, birth weights, morphometrics, and behaviour. However, monkeys born into same- and mixed-sex litters exhibited subtle morphological and neurobehavioral differences later in the perinatal period, independent of their androgen profiles. Our findings suggest that while androgens from male fetuses likely do not organize their siblings' phenotypes, perinatal stimuli may initiate divergent developmental trajectories among siblings, which, in turn, promotes inter-individual variability within families.

Oxytocin modulates mate-guarding behavior in marmoset monkeys

In socially-monogamous species, intolerance of interactions between a pairmate and a sexual rival (i.e., mate-guarding) promotes the preservation of long-lasting partnerships. One promising neurobiological candidate for the regulation of mate-guarding behavior in monogamous primates is the oxytocin (OT) system, given its established role in both the development of monogamous bonds and the behavioral processes that facilitate the preservation of those bonds. In this study, male and female marmosets were exposed to a same-sex intruder in their home environment during conditions when their pairmate was present and absent, and across three treatment conditions (OT receptor agonist; saline control; OT receptor antagonist). Saline-treated marmosets spent significantly more time in proximity to the intruder, relative to the empty pairmate enclosure, when their pairmate was absent. However, when marmosets received OT they spent less time in proximity to the intruder, indicating that OT may reduce interest in a same-sex stranger in a territorial context. When their pairmate was present, saline-treated marmosets spent equal time in proximity to both intruder and pairmate; yet when they received OT they spent significantly more time in proximity to the intruder, indicating that OT may increase interest in a same-sex stranger in a mate-guarding context. While OT treatment did not directly influence the expression of aggression, OT system manipulations impacted the expression of selective social interest during an intruder challenge, suggesting that OT may enhance adaptive responses to social challenges. Moreover, these findings add to the converging evidence that the OT system regulates behavioral processes that underlie the preservation of established relationships.

Oxytocin regulates reunion affiliation with a pairmate following social separation in marmosets

While separation from significant social partners produces a host of neurobiological and behavioral perturbations, including behavioral distress and increased glucocorticoid production, positive social interactions upon reunion are critical for the reestablishment of normative relationship dynamics and the attenuation of the biobehavioral stress response. The hormone oxytocin has critical and pervasive roles in reproductive and behavioral processes across the lifespan, and plays a particularly prominent role in social bonding. In this study, we examined the extent that oxytocin modulates interactions with a pairmate following separation challenges that varied in both social context (isolation; separation) and duration (long; short), in marmosets. We demonstrated that the impact of pharmacological manipulations of the oxytocin system on the expression of affiliation upon reunion depended on both the context and duration of the separation challenge. Specifically, marmosets treated with an oxytocin antagonist spent less time in proximity with their pairmate upon reunion following a long-separation challenge. During the short-separation challenge, marmosets engaged in more social gaze when separated with an opposite-sex stranger, but not when separated with their mate. Furthermore, marmosets that received the most social gaze from opposite-sex strangers spent the most time in proximity with their long-term mate upon reunion. We also showed that marmosets treated with an OT agonist received increased levels of gaze from opposite-sex strangers, but not from their mate. Overall, these results suggest that marmosets are sensitive to the nature of the social interactions during separation, and subsequently alter their expression of affiliation upon reunion with their long-term mate. These findings further implicate oxytocin as a bond-enhancing molecule that regulates the reestablishment of normative levels of affiliation with a mate following separation, and add to the emerging literature that suggests the OT system underlies critical behavioral processes that contribute to the preservation of long-lasting social bonds.

Artificial visual stimuli for animal experiments: An experimental evaluation in a prey capture context with common marmosets (Callithrix jacchus)

Experimenters often use images of real objects to simulate interactions between animal subjects or visual stimuli on a touchscreen to test animal cognition. However, the degree to which nonhuman animals recognize 2-D images as representing the corresponding real objects remains debated. The common marmoset monkey (Callithrix jacchus) has been described as a species that spontaneously shows natural behaviors to 2-D images, for example, grasping behaviors to insects and fear responses to snakes. In this study, we tested 10 monkeys with their favorite food item (crickets), 2-D images (a photo and videos of a cricket), and a 3-D plastic model to reevaluate marmoset's spontaneous responses to 2-D images and to explore which artificial visual stimuli can motivate spontaneous interactions. The monkeys showed grasping behavior to the real cricket and the 3-D plastic model, but to none of the 2-D images. Our experiment suggests that depth information is the most important factor eliciting predatory behavior from the marmosets, and, therefore, a stimulus produced by a 3-D printer could be a good alternative when a spontaneous interaction or a convincing stimulus is required. Furthermore, this work serves as a cautionary tale for those using 2-D image presentations with marmosets, and perhaps other animal species. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Automatic detection and classification of marmoset vocalizations using deep and recurrent neural networks

This paper investigates the methods to detect and classify marmoset vocalizations automatically using a large data set of marmoset vocalizations and deep learning techniques. For vocalization detection, neural networks-based methods, including deep neural network (DNN) and recurrent neural network with long short-term memory units, are designed and compared against a conventional rule-based detection method. For vocalization classification, three different classification algorithms are compared, including a support vector machine (SVM), DNN, and long short-term memory recurrent neural networks (LSTM-RNNs). A 1500-min audio data set containing recordings from four pairs of marmoset twins and manual annotations is employed for experiments. Two test sets are built according to whether the test samples are produced by the marmosets in the training set (test set I) or not (test set II). Experimental results show that the LSTM-RNN-based detection method outperformed others and achieved 0.92% and 1.67% frame error rate on these two test sets. Furthermore, the deep learning models obtained higher classification accuracy than the SVM model, which was 95.60% and 91.67% on the two test sets, respectively.

Top-down feedback controls spatial summation and response amplitude in primate visual cortex

Sensory information travels along feedforward connections through a hierarchy of cortical areas, which, in turn, send feedback connections to lower-order areas. Feedback has been implicated in attention, expectation, and sensory context, but the mechanisms underlying these diverse feedback functions are unknown. Using specific optogenetic inactivation of feedback connections from the secondary visual area (V2), we show how feedback affects neural responses in the primate primary visual cortex (V1). Reducing feedback activity increases V1 cells' receptive field (RF) size, decreases their responses to stimuli confined to the RF, and increases their responses to stimuli extending into the proximal surround, therefore reducing surround suppression. Moreover, stronger reduction of V2 feedback activity leads to progressive increase in RF size and decrease in response amplitude, an effect predicted by a recurrent network model. Our results indicate that feedback modulates RF size, surround suppression and response amplitude, similar to the modulatory effects of visual spatial attention.

Individual identity and affective valence in marmoset calls: in vivo brain imaging with vocal sound playback

As with humans, vocal communication is an important social tool for nonhuman primates. Common marmosets (Callithrix jacchus) often produce whistle-like 'phee' calls when they are visually separated from conspecifics. The neural processes specific to phee call perception, however, are largely unknown, despite the possibility that these processes involve social information. Here, we examined behavioral and whole-brain mapping evidence regarding the detection of individual conspecific phee calls using an audio playback procedure. Phee calls evoked sound exploratory responses when the caller changed, indicating that marmosets can discriminate between caller identities. Positron emission tomography with [18F] fluorodeoxyglucose revealed that perception of phee calls from a single subject was associated with activity in the dorsolateral prefrontal, medial prefrontal, orbitofrontal cortices, and the amygdala. These findings suggest that these regions are implicated in cognitive and affective processing of salient social information. However, phee calls from multiple subjects induced brain activation in only some of these regions, such as the dorsolateral prefrontal cortex. We also found distinctive brain deactivation and functional connectivity associated with phee call perception depending on the caller change. According to changes in pupillary size, phee calls from a single subject induced a higher arousal level compared with those from multiple subjects. These results suggest that marmoset phee calls convey information about individual identity and affective valence depending on the consistency or variability of the caller. Based on the flexible perception of the call based on individual recognition, humans and marmosets may share some neural mechanisms underlying conspecific vocal perception.

Limiting parental interaction during vocal development affects acoustic call structure in marmoset monkeys

Human vocal development is dependent on learning by imitation through social feedback between infants and caregivers. Recent studies have revealed that vocal development is also influenced by parental feedback in marmoset monkeys, suggesting vocal learning mechanisms in nonhuman primates. Marmoset infants that experience more contingent vocal feedback than their littermates develop vocalizations more rapidly, and infant marmosets with limited parental interaction exhibit immature vocal behavior beyond infancy. However, it is yet unclear whether direct parental interaction is an obligate requirement for proper vocal development because all monkeys in the aforementioned studies were able to produce the adult call repertoire after infancy. Using quantitative measures to compare distinct call parameters and vocal sequence structure, we show that social interaction has a direct impact not only on the maturation of the vocal behavior but also on acoustic call structures during vocal development. Monkeys with limited parental interaction during development show systematic differences in call entropy, a measure for maturity, compared with their normally raised siblings. In addition, different call types were occasionally uttered in motif-like sequences similar to those exhibited by vocal learners, such as birds and humans, in early vocal development. These results indicate that a lack of parental interaction leads to long-term disturbances in the acoustic structure of marmoset vocalizations, suggesting an imperative role for social interaction in proper primate vocal development.

Investigation of the BOLD and CBV fMRI responses to somatosensory stimulation in awake marmosets (Callithrix jacchus)

Understanding the spatiotemporal features of the hemodynamic response function (HRF) to brain stimulation is essential for the correct application of neuroimaging methods to study brain function. Here, we investigated the spatiotemporal evolution of the blood oxygen level-dependent (BOLD) and cerebral blood volume (CBV) HRF in conscious, awake marmosets (Callithrix jacchus), a New World non-human primate with a lissencephalic brain and with growing use in biomedical research. The marmosets were acclimatized to head fixation and placed in a 7-T magnetic resonance imaging (MRI) scanner. Somatosensory stimulation (333-μs pulses; amplitude, 2 mA; 64 Hz) was delivered bilaterally via pairs of contact electrodes. A block design paradigm was used in which the stimulus duration increased in pseudo-random order from a single pulse up to 256 electrical pulses (4 s). For CBV measurements, 30 mg/kg of ultrasmall superparamagnetic ironoxide particles (USPIO) injected intravenously, were used. Robust BOLD and CBV HRFs were obtained in the primary somatosensory cortex (S1), secondary somatosensory cortex (S2) and caudate at all stimulus conditions. In particular, BOLD and CBV responses to a single 333-μs-long stimulus were reliably measured, and the CBV HRF presented shorter onset time and time to peak than the BOLD HRF. Both the size of the regions of activation and the peak amplitude of the HRFs grew quickly with increasing stimulus duration, and saturated for stimulus durations greater than 1 s. Onset times in S1 and S2 were faster than in caudate. Finally, the fine spatiotemporal features of the HRF in awake marmosets were similar to those obtained in humans, indicating that the continued refinement of awake non-human primate models is essential to maximize the applicability of animal functional MRI studies to the investigation of human brain function.

Reverse audience effects on helping in cooperatively breeding marmoset monkeys

Cooperatively breeding common marmosets show substantial variation in the amount of help they provide. Pay-to-stay and social prestige models of helping attribute this variation to audience effects, i.e. that individuals help more if group members can witness their interactions with immatures, whereas models of kin selection, group augmentation or those stressing the need to gain parenting experience do not predict any audience effects. We quantified the readiness of adult marmosets to share food in the presence or absence of other group members. Contrary to both predictions, we found a reverse audience effect on food-sharing behaviour: marmosets would systematically share more food with immatures when no audience was present. Thus, helping in common marmosets, at least in related family groups, does not support the pay-to-stay or the social prestige model, and helpers do not take advantage of the opportunity to engage in reputation management. Rather, the results appear to reflect a genuine concern for the immatures' well-being, which seems particularly strong when solely responsible for the immatures.

Larger cages with housing unit environment enrichment improve the welfare of marmosets

The provision of adequate space for laboratory animals is essential not only for good welfare but accurate studies. For example, housing conditions for primates used in biomedical research may negatively affect welfare and thus the reliability of findings. In common marmosets (Callithrix jacchus), an appropriate cage size enables a socially harmonious family environment and optimizes reproductive potential. In this study, we investigated the effects of cage size on body weight (BW), behavior, and nursing succession in the common marmoset. Large cages (LCs) with environment enrichment led to an increase in BW while small cages (SCs) caused stereotypic behaviors that were not observed in LCs. In addition, the BW of infants increased with aging in LCs. Our findings indicate that the welfare of marmosets was enhanced by living in LCs. Research on non-human primates is essential for understanding the human brain and developing knowledge-based strategies for the diagnosis and treatment of psychiatric and neurological disorders. Thus, the present findings are important because they indicate that different cages may influence emotional and behavioral phenotypes.

Transient visual pathway critical for normal development of primate grasping behavior

An evolutionary hallmark of anthropoid primates, including humans, is the use of vision to guide precise manual movements. These behaviors are reliant on a specialized visual input to the posterior parietal cortex. Here, we show that normal primate reaching-and-grasping behavior depends critically on a visual pathway through the thalamic pulvinar, which is thought to relay information to the middle temporal (MT) area during early life and then swiftly withdraws. Small MRI-guided lesions to a subdivision of the inferior pulvinar subnucleus (PIm) in the infant marmoset monkey led to permanent deficits in reaching-and-grasping behavior in the adult. This functional loss coincided with the abnormal anatomical development of multiple cortical areas responsible for the guidance of actions. Our study reveals that the transient retino-pulvinar-MT pathway underpins the development of visually guided manual behaviors in primates that are crucial for interacting with complex features in the environment.

Vocal development through morphological computation

The vocal behavior of infants changes dramatically during early life. Whether or not such a change results from the growth of the body during development-as opposed to solely neural changes-has rarely been investigated. In this study of vocal development in marmoset monkeys, we tested the putative causal relationship between bodily growth and vocal development. During the first two months of life, the spontaneous vocalizations of marmosets undergo (1) a gradual disappearance of context-inappropriate call types and (2) an elongation in the duration of context-appropriate contact calls. We hypothesized that both changes are the natural consequences of lung growth and do not require any changes at the neural level. To test this idea, we first present a central pattern generator model of marmoset vocal production to demonstrate that lung growth can affect the temporal and oscillatory dynamics of neural circuits via sensory feedback from the lungs. Lung growth qualitatively shifted vocal behavior in the direction observed in real marmoset monkey vocal development. We then empirically tested this hypothesis by placing the marmoset infants in a helium-oxygen (heliox) environment in which air is much lighter. This simulated a reversal in development by decreasing the effort required to respire, thus increasing the respiration rate (as though the lungs were smaller). The heliox manipulation increased the proportions of inappropriate call types and decreased the duration of contact calls, consistent with a brief reversal of vocal development. These results suggest that bodily growth alone can play a major role in shaping the development of vocal behavior.

Rate, not selectivity, determines neuronal population coding accuracy in auditory cortex

The notion that neurons with higher selectivity carry more information about external sensory inputs is widely accepted in neuroscience. High-selectivity neurons respond to a narrow range of sensory inputs, and thus would be considered highly informative by rejecting a large proportion of possible inputs. In auditory cortex, neuronal responses are less selective immediately after the onset of a sound and then become highly selective in the following sustained response epoch. These 2 temporal response epochs have thus been interpreted to encode first the presence and then the content of a sound input. Contrary to predictions from that prevailing theory, however, we found that the neural population conveys similar information about sound input across the 2 epochs in spite of the neuronal selectivity differences. The amount of information encoded turns out to be almost completely dependent upon the total number of population spikes in the read-out window for this system. Moreover, inhomogeneous Poisson spiking behavior is sufficient to account for this property. These results imply a novel principle of sensory encoding that is potentially shared widely among multiple sensory systems.

Common marmoset (Callithrix jacchus) personality

Increasing evidence suggests that personality structure differs between species, but the evolutionary reasons for this variation are not fully understood. We built on earlier research on New World monkeys to further elucidate the evolution of personality structure in primates. We therefore examined personality in 100 family-reared adult common marmosets (Callithrix jacchus) from 3 colonies on a 60-item questionnaire. Principal components analyses revealed 5 domains that were largely similar to those found in a previous study on captive, ex-pet, or formerly laboratory-housed marmosets that were housed in a sanctuary. The interrater reliabilities of domain scores were consistent with the interrater reliabilities of domain scores found in other species, including humans. Four domainsdmdash;conscientiousness, agreeableness, inquisitiveness, and assertiveness-resembled personality domains identified in other nonhuman primates. The remaining domain, patience, was specific to common marmosets. We used linear models to test for sex and age differences in the personality domains. Males were lower than females in patience, and this difference was smaller in older marmosets. Older marmosets were lower in inquisitiveness. Finally, older males and younger females had higher scores in agreeableness than younger males and older females. These findings suggest that cooperative breeding may have promoted the evolution of social cognition and influenced the structure of marmoset prosocial personality characteristics. (PsycINFO Database Record