Group differences in activity during Video Playback probe.

<p>Manifestly low sociable (MLS) monkeys display greater activity (position changes between front and back of cage) than do truly low sociable (TLS) monkeys while watching the fearful/submissive videotape. No group differences were found for the Aggression or Neutral videotape displays.</p

Behavioral definitions for Video Playback and Human Intruder probes.

<p>Behavioral definitions for Video Playback and Human Intruder probes.</p

Differences between three groups of monkeys, from two samples, on measures of tentative social interaction.

<p>A. Manifestly low sociable (MLS) and high sociable (HS) monkeys from Sample 1 show comparable levels of approach and walkby, and frequencies for both groups are significantly higher than for those of the truly low sociable (TLS) group. B. MLS and HS monkeys from Sample 2 show comparable levels of approach to each other, but are significantly higher than those among TLS monkeys.</p

A Behavioral Taxonomy of Loneliness in Humans and Rhesus Monkeys (<i>Macaca mulatta</i>)

<div><p>Social relationships endow health and fitness benefits, but considerable variation exists in the extent to which individuals form and maintain salutary social relationships. The mental and physical health effects of social bonds are more strongly related to perceived isolation (loneliness) than to objective social network characteristics. We sought to develop an animal model to facilitate the experimental analysis of the development of, and the behavioral and biological consequences of, loneliness. In <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110307#s2" target="_blank">Study 1</a>, using a population-based sample of older adults, we examined how loneliness was influenced both by social network size and by the extent to which individuals believed that their daily social interactions reflected their own choice. Results revealed three distinct clusters of individuals: (i) individuals with large networks who believed they had high choice were lowest in loneliness, (ii) individuals with small social networks who believed they had low choice were highest in loneliness, and (iii) the remaining two groups were intermediate and equivalent in loneliness. In <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110307#s3" target="_blank">Study 2</a>, a similar three-group structure was identified in two separate samples of adult male rhesus monkeys (<i>Macaca mulatta</i>) living in large social groups: (i) those high in sociability who had complex social interaction with a broad range of social partners (putatively low in loneliness), (ii) those low in sociability who showed tentative interactions with certain classes of social partners (putatively high in loneliness), and (iii) those low in sociability who interacted overall at low levels with a broad range of social partners (putatively low or intermediate in loneliness). This taxonomy in monkeys was validated in subsequent experimental social probe studies. These results suggest that, in highly social nonhuman primate species, some animals may show a mismatch between social interest and social attainment that could serve as a useful animal model for experimental and mechanistic studies of loneliness.</p></div

Mean (SD) frequencies for walkby and approach for MLS and TLS animals from Samples 1 and 2.

<p>Values shown are means and SD; significance tests were based on log-transformed values as needed.</p><p>*indicates significant differences (see text) between MLS and TLS animals.</p><p>Mean (SD) frequencies for walkby and approach for MLS and TLS animals from Samples 1 and 2.</p

Group differences in loneliness among humans.

<p>Individuals with low social choice (LC) and small social networks (SN) have levels of loneliness that are significantly greater than individuals with high choice (HC) and large networks (LN). Individuals with low choice/large networks and those with high choice/small networks were not different from each other, but were significantly different from the other two groups.</p

Group differences in positional and agonistic responses during a Human Intruder challenge.

<p>Manifestly low sociable (MLS) monkeys A) are more frequently in the front of the cage than are TLS monkeys, but only in low-challenge (profile orientation) conditions, and B) show higher frequencies of grimace and cage shake during high-challenge (stare orientation) conditions.</p

Behavioral Inhibition in Rhesus Monkeys (<i>Macaca mulatta</i>) Is Related to the Airways Response, but Not Immune Measures, Commonly Associated with Asthma

<div><p>Behavioral inhibition reflects a disposition to react warily to novel situations, and has been associated with atopic diseases such as asthma. Retrospective work established the relationship between behavioral inhibition in rhesus monkeys (<i>Macaca mulatta</i>) and airway hyperresponsiveness, but not atopy, and the suggestion was made that behavioral inhibition might index components of asthma that are not immune-related. In the present study, we prospectively examined the relationship between behavioral inhibition and airway hyperresponsiveness, and whether hormonal and immune measures often associated with asthma were associated with behavioral inhibition and/or airway hyperresponsiveness. In a sample of 49 yearling rhesus monkeys (mean = 1.25 years, n = 24 behaviorally inhibited animals), we measured <i>in vitro</i> cytokine levels (IL-4, IL-10, IL-12, IFN-γ) in response to stimulation, as well as peripheral blood cell percentages, cortisol levels, and percentage of regulatory T-cells (CD3+CD4+CD25+FOXP3+). Airway reactivity was assessed using an inhaled methacholine challenge. Bronchoalveolar lavage was performed and the proportion of immune cells was determined. Behaviorally inhibited monkeys had airway hyperresponsiveness as indicated by the methacholine challenge (p = 0.031), confirming our earlier retrospective result. Airway hyperresponsiveness was also associated with lower lymphocyte percentages in lavage fluid and marginally lower plasma cortisol concentrations. However, none of the tested measures was significantly related to both behavioral inhibition and airway hyperresponsiveness, and so could not mediate their relationship. Airway hyperresponsiveness is common to atopic and non-atopic asthma and behavioral inhibition has been related to altered autonomic activity in other studies. Our results suggest that behavioral inhibition might index an autonomically mediated reactive airway phenotype, and that a variety of stimuli (including inflammation within lung tissue that is not specifically associated with behavioral inhibition) may trigger the airways response.</p></div

Yearling assessments study design and outcome measures.

<p>CBC = complete blood count.</p><p>PBMC = peripheral blood mononuclear cell isolation.</p><p>PFT = pulmonary function test.</p><p>BALF = bronchoalveolar lavage fluid collection.</p

Correlation coefficients between physiological measures, behavioral inhibition, and AHR.

<p>Values expressed are Pearson product-moment correlation coefficients, unless designated by ^†, which reflect partial correlation coefficients (see text).</p>*<p>p<0.05.</p><p>+p<0.10.</p><p>AHR = Airway hyperresponsiveness.</p><p>IL = Interleukin.</p><p>IFN = Interferon.</p