In memory of our mentor: Frans de Waal (1948-2024).

The world lost a towering figure when primatologist Frans de Waal passed away on March 14, 2024. Many are aware of his multitude of contributions to the field. His ability to see what animals were actually doing changed how we viewed first primates, then other species. He shared these insights through both traditional scientific outputs, such as journal articles and scientific presentations, and less common outputs, such as 15 books and two TED talks viewed millions of times. What may be less well known is his impact as a mentor. Here, 25 of us who were Frans' graduate students, postdocs, and long-term research assistants share his personal impact on our lives.

Insight meditation and telomere biology: The effects of intensive retreat and the moderating role of personality.

A growing body of evidence suggests that meditation training may have a range of salubrious effects, including improved telomere regulation. Telomeres and the enzyme telomerase interact with a variety of molecular components to regulate cell-cycle signaling cascades, and are implicated in pathways linking psychological stress to disease. We investigated the effects of intensive meditation practice on these biomarkers by measuring changes in telomere length (TL), telomerase activity (TA), and telomere-related gene (TRG) expression during a 1-month residential Insight meditation retreat. Multilevel analyses revealed an apparent TL increase in the retreat group, compared to a group of experienced meditators, similarly comprised in age and gender, who were not on retreat. Moreover, personality traits predicted changes in TL, such that retreat participants highest in neuroticism and lowest in agreeableness demonstrated the greatest increases in TL. Changes observed in TRGs further suggest retreat-related improvements in telomere maintenance, including increases in Gar1 and HnRNPA1, which encode proteins that bind telomerase RNA and telomeric DNA. Although no group-level changes were observed in TA, retreat participants' TA levels at post-assessment were inversely related to several indices of retreat engagement and prior meditation experience. Neuroticism also predicted variation in TA across retreat. These findings suggest that meditation training in a retreat setting may have positive effects on telomere regulation, which are moderated by individual differences in personality and meditation experience. (ClinicalTrials.gov #NCT03056105).

Monkeys recognize the faces of group mates in photographs.

Nonhuman primates possess a highly developed capacity for face recognition, which resembles the human capacity both cognitively and neurologically. Face recognition is typically tested by having subjects compare facial images, whereas there has been virtually no attention to how they connect these images to reality. Can nonhuman primates recognize familiar individuals in photographs? Such facial identification was examined in brown or tufted capuchin monkeys (Cebus apella), a New World primate, by letting subjects categorize facial images of conspecifics as either belonging to the in-group or out-group. After training on an oddity task with four images on a touch screen, subjects correctly identified one in-group member as odd among three out-group members, and vice versa. They generalized this knowledge to both new images of the same individuals and images of juveniles never presented before, thus suggesting facial identification based on real-life experience with the depicted individuals. This ability was unexplained by potential color cues because the same results were obtained with grayscale images. These tests demonstrate that capuchin monkeys, like humans, recognize whom they see in a picture.

An inversion effect modified by expertise in capuchin monkeys.

The face inversion effect may be defined as the general impairment in recognition that occurs when faces are rotated 180°. This phenomenon seems particularly strong for faces as opposed to other objects and is often used as a marker of a specialized face-processing mechanism. Four brown capuchin monkeys (Cebus apella) were tested on their ability to discriminate several classes of facial and non-facial stimuli presented in both their upright and inverted orientations in an oddity task. Results revealed significantly better performance on upright than inverted presentations of capuchin and human face stimuli, but not on chimpanzee faces or automobiles. These data support previous studies in humans and other primates suggesting that the inversion effect occurs for stimuli for which subjects have developed an expertise.

Face recognition in capuchin monkeys (Cebus apella).

Primates live in complex social groups that necessitate recognition of the individuals with whom they interact. In humans, faces provide a visual means by which to gain information such as identity, allowing us to distinguish between both familiar and unfamiliar individuals. The current study used a computerized oddity task to investigate whether a New World primate, Cebus apella, can discriminate the faces of In-group and Out-group conspecifics based on identity. The current study, improved on past methodologies, demonstrates that capuchins recognize the faces of both familiar and unfamiliar conspecifics. Once a performance criterion had been reached, subjects successfully transferred to a large number of novel images within the first 100 trials thus ruling out performance based on previous conditioning. Capuchins can be added to a growing list of primates that appear to recognize two-dimensional facial images of conspecifics.

Neural Processing and Production of Gesture in Children and Adolescents With Autism Spectrum Disorder.

Individuals with autism spectrum disorder (ASD) demonstrate impairments in non-verbal communication, including gesturing and imitation deficits. Reduced sensitivity to biological motion (BM) in ASD may impair processing of dynamic social cues like gestures, which in turn may impede encoding and subsequent performance of these actions. Using both an fMRI task involving observation of action gestures and a charade style paradigm assessing gesture performance, this study examined the brain-behavior relationships between neural activity during gesture processing, gesturing abilities and social symptomology in a group of children and adolescents with and without ASD. Compared to typically developing (TD) controls, participants with ASD showed atypical sensitivity to movement in right posterior superior temporal sulcus (pSTS), a region implicated in action processing, and had poorer overall gesture performance with specific deficits in hand posture. The TD group showed associations between neural activity, gesture performance and social skills, that were weak or non-significant in the ASD group. These findings suggest that those with ASD demonstrate abnormalities in both processing and production of gestures and may reflect dysfunction in the mechanism underlying perception-action coupling resulting in atypical development of social and communicative skills.

What Are You Doing With That Object? Comparing the Neural Responses of Action Understanding in Adolescents With and Without Autism.

Understanding another's actions, including what they are doing and why they are doing it, can be difficult for individuals with autism spectrum disorder (ASD). This understanding is supported by the action observation (AON) and mentalizing (MZN) networks, as well as the superior temporal sulcus. We examined these areas in children with ASD and typically developing controls by having participants view eating and placing actions performed in conventional and unconventional ways while functional magnetic resonance images were collected. We found an effect of action-type, but not conventionality, in both groups, and a between groups difference only when viewing conventional eating actions. Findings suggest there are not global AON/MZN deficits in ASD, and observing unconventional actions may not spontaneously activate the MZN.

Network analysis for the visualization and analysis of qualitative data.

We present a novel manner in which to visualize the coding of qualitative data that enables representation and analysis of connections between codes using graph theory and network analysis. Network graphs are created from codes applied to a transcript or audio file using the code names and their chronological location. The resulting network is a representation of the coding data that characterizes the interrelations of codes. This approach enables quantification of qualitative codes using network analysis and facilitates examination of associations of network indices with other quantitative variables using common statistical procedures. Here, as a proof of concept, we applied this method to a set of interview transcripts that had been coded in 2 different ways and the resultant network graphs were examined. The creation of network graphs allows researchers an opportunity to view and share their qualitative data in an innovative way that may provide new insights and enhance transparency of the analytical process by which they reach their conclusions. (PsycINFO Database Record

Discrimination of emotional facial expressions by tufted capuchin monkeys (Sapajus apella).

Tufted or brown capuchin monkeys (Sapajus apella) have been shown to recognize conspecific faces as well as categorize them according to group membership. Little is known, though, about their capacity to differentiate between emotionally charged facial expressions or whether facial expressions are processed as a collection of features or configurally (i.e., as a whole). In 3 experiments, we examined whether tufted capuchins (a) differentiate photographs of neutral faces from either affiliative or agonistic expressions, (b) use relevant facial features to make such choices or view the expression as a whole, and (c) demonstrate an inversion effect for facial expressions suggestive of configural processing. Using an oddity paradigm presented on a computer touchscreen, we collected data from 9 adult and subadult monkeys. Subjects discriminated between emotional and neutral expressions with an exceptionally high success rate, including differentiating open-mouth threats from neutral expressions even when the latter contained varying degrees of visible teeth and mouth opening. They also showed an inversion effect for facial expressions, results that may indicate that quickly recognizing expressions does not originate solely from feature-based processing but likely a combination of relational processes. (PsycINFO Database Record

The Action Observation System when Observing Hand Actions in Autism and Typical Development.

Social impairments in individuals with autism spectrum disorders (ASD) may be in part due to difficulty perceiving and recognizing the actions of others. Evidence from imitation studies, which involves both observation and execution of an action, suggests differences, in individuals with ASD, between the ability to imitate goal-directed actions involving objects (transitive actions) and the ability to imitate actions that do not involve objects (intransitive actions). In the present study, we examined whether there were differences in how ASD adolescents encoded transitive and intransitive actions compared to typically developing (TD) adolescents, by having participants view videos of a hand reaching across a screen toward an object or to where an object would be while functional magnetic resonance images were collected. Analyses focused on areas within the action observation network (AON), which is activated during the observation of actions performed by others. We hypothesized that the AON would differentiate transitive from intransitive actions only in the ASD group. However, results revealed that object presence modulated activity in the right inferior frontal gyrus and supramarginal gyrus of the TD group, a differentiation that was not seen in the ASD group. Furthermore, there were no significant group differences between the TD and ASD groups in any of the conditions. This suggests that there is not a global deficit of the AON in individuals with ASD while observing transitive and intransitive actions.

Visual cues given by humans are not sufficient for Asian elephants (Elephas maximus) to find hidden food.

Recent research suggests that domesticated species--due to artificial selection by humans for specific, preferred behavioral traits--are better than wild animals at responding to visual cues given by humans about the location of hidden food. \Although this seems to be supported by studies on a range of domesticated (including dogs, goats and horses) and wild (including wolves and chimpanzees) animals, there is also evidence that exposure to humans positively influences the ability of both wild and domesticated animals to follow these same cues. Here, we test the performance of Asian elephants (Elephas maximus) on an object choice task that provides them with visual-only cues given by humans about the location of hidden food. Captive elephants are interesting candidates for investigating how both domestication and human exposure may impact cue-following as they represent a non-domesticated species with almost constant human interaction. As a group, the elephants (n = 7) in our study were unable to follow pointing, body orientation or a combination of both as honest signals of food location. They were, however, able to follow vocal commands with which they were already familiar in a novel context, suggesting the elephants are able to follow cues if they are sufficiently salient. Although the elephants' inability to follow the visual cues provides partial support for the domestication hypothesis, an alternative explanation is that elephants may rely more heavily on other sensory modalities, specifically olfaction and audition. Further research will be needed to rule out this alternative explanation.

Activity of substantia nigra pars reticulata neurons during smooth pursuit eye movements in monkeys.

Nuclei within the basal ganglia (BG), in particular the substantia nigra pars reticulata (SNr), subthalamic nucleus (STN) and caudate nucleus, are known to be involved in the generation of rapid or saccadic eye movements. Neurons in the SNr are active tonically and generally show a pause, but also increase, in discharge rate, for the appearance of visual stimuli and the generation of saccades. Recent experimental results in oculomotor regions of the brainstem reveal overlap in the neuronal pathways used for saccades and smooth pursuit, or slow tracking, eye movements. Whether the overlap of processing for saccades and pursuit extends to the oculomotor BG is unknown. In the present report, we were interested in whether the overlap between the pursuit and saccadic systems extends into the oculomotor BG. Using single-neuron recording and electrical stimulation techniques, we tested whether neurons within the saccade portion of the BG, the SNr, could be involved in smooth pursuit eye movements. Monkeys were required to follow visual targets with either a smooth eye movement or a saccade while we recorded from SNr neurons. We report here on SNr neuronal activity that was modulated during the performance of visually guided saccades and also during the initiation and the maintenance of smooth pursuit eye movements. Importantly, the modulation of neuronal activity during pursuit was present even when catch-up saccades were absent. The majority of SNr neurons was active tonically and their discharge ceased during pursuit, although some neurons also increased their discharge rate during smooth pursuit, similar to the behaviour reported for saccades. We also found that electrical stimulation of the SNr during the initiation of pursuit suppressed ipsiversive and, in some cases, enhanced contraversive pursuit. Our combined recording and stimulation results are consistent with the hypothesis that the overlap between the pursuit and saccadic systems extends, at least somewhat, into the BG and that the signal conveyed by the SNr can be used by the pursuit system. Like the signal for saccades, the SNr may provide a permissive disinhibition for pursuit eye movements. We hypothesize that alterations in this signal in BG diseased states such as Parkinson's may explain in part the deficits observed in smooth pursuit eye movements of these patients.