To our knowledge, however, gibbons have never been tested with these quantities. Nevertheless, in our scenario gibbons did not necessarily need to discern between these two quantities because the two amounts were never presented at the same time. Thus, although it is possible that this difference could have played a role in their performance, it is more parsimonious to think that their motivation to pull in direct food test trials was due to the high probability to eat the extra reward while pulling the handle. Future studies may use different reward constellations varying in quantity and/or quality to continue shedding light on gibbon socio-cognitive performance. Finally, given the quasi-experimental nature of our task, we did not always capture the social dilemma scenario we envisioned. Future tasks should implement designs in which cooperative acts are clearly costly for those individuals willing to volunteer. In addition, given our restricted sample size we could not test species differences or the presence of individual biases . Te present study advances our understanding of how tolerance may allow primates to solve potential conflict over food rewards. In our study gibbons exhibit high degrees of social tolerance . Passive partners tolerate that actors obtain higher benefits in a majority of trials while actors often actively forego opportunities to maximize rewards . Relatedly, gibbons engaged in cofeeding events relatively often. One possibility is that such a high degree of social tolerance towards conspecifics results from gibbons’ unique pairliving social system compared to other great apes,hydroponic dutch buckets although future studies should inspect this relationship in more detail. Overall, the inclusion of gibbons in studies exploring the nature of primate socio-cognitive abilities is critical.
It will help to elucidate the nature of our prosocial motivations and their relationship to specific socio-ecological pressures and ultimately to understand how they have evolved since the last common ancestor with all living apes.One experimenter interacted with the apes during a test session while a second experimenter recorded the session and scored the subjects behavior . Each experimenter tested half of the dyads. We used high quality rewards that would be easily visible to the subjects. Blueberries were not part of their daily diet but were sometimes presented as enrichment in puzzle feeders and were highly desirable for all gibbons housed at the GCC. Te apparatus was composed of a plastic folding table with a square wooden plank clamped to the top. At one end of the plank a transparent plastic bin was taped so that it could be lifed up or hang down. Te bin, at rest, would hang down and remain unmoved on the top of a wooden ramp. A hole big enough to ft blueberries was drilled on the back side of the bin so that when at rest on the ramp, the experimenter could place five blueberries into the bin. A thin purple rope was tied to the far end of the plastic bin and was routed back to the opposite end of the wooden plank. This was set up so that pulling on the purple rope would reliably life the plastic bin, so blueberries could fall down the wooden ramp and be easily accessible for subjects to obtain. Te extreme end of the rope was attached to the mesh of the enclosure. To allow reaching and pulling the rope, we attached a small, handheld, opaque white handle . At the right tension, pulling on the handle would reliably life the plastic bin. Te handle could contain a single blueberry inside depending on the condition presented. We used two handles of the same dimensions and appearance to avoid contamination of blueberry lefovers after the trial. Te table with wooden plank would be set up at a distance so that it could not be grabbed by subjects and the ramp was placed underneath so that blueberries would roll down and land in front of the enclosure gate.
E2 would then distract the two subjects to an opposite or adjacent side of the subjects’ enclosure with a handful of cereal pieces while E1 tied the end of the purple rope with the handle onto the mesh gate of the enclosure, roughly at the experimenter height, approximately 2 m to the right or left. Te distance and location of the rope was kept constant for all trials of each dyad; however, because the enclosures differed in layout, the rope would go to the most convenient side. This way, we ensured that the rope had proper tension to be pulled by gibbons and life the plastic bin as well as be distant enough from the ramp so that a subject could not easily pull on the rope and obtain food from the ramp at the same time.Individual solo pre-testing of the mechanism of the apparatus was not possible because the separation of the dyads was prohibited. However, gibbons had had experience with ropes before as part of their enrichment and several individuals had participated in pilot sessions where they had to pull from different ropes and handles. Tree conditions were tested: direct food test condition, indirect food test condition and no food control condition. In the direct food test condition, the following procedure was performed. E1 would place five blueberries in the plastic bin on the apparatus. To gain the attention of the subjects, E1 would call the subjects names and show the food, if they were not already focused on the food/experimenter. Once both subjects had observed the five blueberries placed in the plastic bin, E1 would squeeze a single blueberry on top of the handle, so that the blueberry would be clearly visible. Te rope and handle would be set up so that the handle was just far enough from the enclosure in order for subjects to need to pull on the rope to obtain access to the handle and blueberry. Consequently, pulling the rope would also life the plastic bin and drop five blueberries down the ramp, accessible to subjects. Te experimenter would also call the names of the subjects when placing the single blueberry in the handle. A choice was recorded when one of the subjects pulled the rope. If no subject pulled the rope within 90 s, the trial ended and was recorded as no pull. If an experimenter error was made , up to 3 repetitions of the trial would be completed.
Environmental conditions such as rain would also end test sessions to be continued the next day. In the indirect food test condition, there was no single blueberry placed in the handle. To compare conditions, we followed the same procedure as in the direct food test condition. Instead of inserting a blueberry inside the handle, we approached it with the first close and then we touched it with the fingers. In the no food control condition, no blueberries were used in the trial. In order to control for time and actions, we used the same procedure of calling the subjects and touching both the box and the handle.Two cameras on tripods recorded footage concurrently. One was placed to the side of the experimenter in order to capture a wide view of the trials, specifically to show the positions of the subjects, their choices and if they obtained blueberries. Te other was placed close to the ramp to accurately count the quantity of blueberries obtained by each subject. For all trials we coded the act of pulling or not pulling and the ID of the puller and non-puller . We also coded the number of blueberries each subject ate and whether the actor subject ate the blueberry from the handle. Next,bato bucket we coded whether a passive subject was present in front of the ramp or within one meter from it at the moment the plastic bin was lifed and at the moment the actor arrived at the release location. Additionally, we coded instances of cofeeding and displacements. Cofeeding was coded when individuals feed within a distance of 1 m of one another. Displacements occurred when an individual left her spot due to the partners’ arrival. Additionally, we calculated the latency to pull from the start of the trial until the individual releases . All analyses were conducted with R statistics . We used Generalized Linear Mixed Models to investigate gibbons’ choices . Covariates were z-transformed. Every full model was compared to a null model excluding the test variables. We controlled for session and trial number in all our models. We controlled for the length of the dyad in models 1 to 3 given the larger dataset compared to models 4 to 6. In addition, in model 3 we included individuals’ age and sex as control predictors. When the comparison between the full and the null model was significant, we further investigated the significance of the test variables and/or their interactions. We used the “drop1” function of the lme4 package68 to test each variable significance including interactions between test predictors. A likelihood ratio test with significance set at p<0.05 was used to compare models and to test the significance of the individual fixed effects. We ruled out collinearity by checking Variance Infation Factors . All VIF values were close to 1 except for age and length of dyad in model 3. Te two variables were slightly collinear . For every model we assessed its stability by comparing the estimates derived by a model based on all data with those obtained from models with the levels of the random effects excluded one at a time. All models were stable. We also fitted a mixed-effects Cox proportional hazards model to analyze gibbons’ latencies to act. For this purpose, we used the “coxme” function from the coxme package. Te results of Model 2 are reported as hazard ratios .
An HR greater than one indicates an increased likelihood of acting and an HR smaller than 1 indicated a decreased hazard of acting. In addition, to obtain the p-values for the individual fixed effects we conducted likelihood-ratio tests.The human brain requires a constant movement of blood through a network of cerebral arteries and veins to deliver oxygen, glucose, and other essential nutrients, but also to remove carbon dioxide, lactic acid, and other metabolic products. CBF in adults represents approximately 15% of the total cardiac output, while the brain accounts for only 2% of total body weight. Regional blood flow, which is tightly regulated to meet the metabolic demands of the brain, varies significantly between gray and white matter, and among different gray matter regions. After adolescence, cerebral blood flow stays relatively stable for a long period, after which it steadily declines. In fact, in middle-aged and elderly adults, aging accounts for a decrease of approximately 0.45% to 0.50% in global CBF per year. It has been shown that, likewise, perfusion through both cortical regions of the cerebral cortex decreases with age, especially in the frontal, temporal, and parietal lobes, and subcortical regions. Aging is also a main risk factor for cognitive impairment and dementia. In elderly subjects, regional CBF in the superior temporal gyrus was positively associated with global cognitive performance. Furthermore, lifestyle factors increased global and regional CBF, and these lifestyle-induced changes in cerebral perfusion may improve cognitive functioning. These relationships are schematically depicted in Figure 1. Differences in CBF between elderly subjects are related to vascular risk factors as well as risk factors for dementia. Bangen and colleagues have observed that the presence of multiple vascular risk factors may add to the already diminished cerebral perfusion that results from aging. It has also been shown that mean gray matter CBF was 15% lower in late middle-aged subjects suffering from metabolic syndrome than age-matched healthy subjects, and was associated with lower cognitive function. Moreover, in the elderly, reduced cerebral perfusion correlated with the volume of white matter hyper intensities and cortical microbleeds, which are established risk factors for dementia. Neurovascular coupling is another critical component that affects CBF and consequently cognitive function. This phenomenon refers to the close temporal and regional relationship between neural activity elicited, for example, by a cognitive task and subsequent changes detected in cerebral perfusion. In particular, aging impairs the mechanisms that match oxygen and nutrient delivery with the increased metabolic demands in active brain region.