Context-independent encoding of passive and active self-motion in vestibular afferent fibers during locomotion in primates

The vestibular system detects head motion to coordinate vital reflexes and provide our sense of balance and spatial orientation. A long-standing hypothesis has been that projections from the central vestibular system back to the vestibular sensory organs (i.e., the efferent vestibular system) mediate adaptive sensory coding during voluntary locomotion. However, direct proof for this idea has been lacking. Here we recorded from individual semicircular canal and otolith afferents during walking and running in monkeys. Using a combination of mathematical modeling and nonlinear analysis, we show that afferent encoding is actually identical across passive and active conditions, irrespective of context. Thus, taken together our results are instead consistent with the view that the vestibular periphery relays robust information to the brain during primate locomotion, suggesting that context-dependent modulation instead occurs centrally to ensure that coding is consistent with behavioral goals during locomotion.

Metacarpophalangeal joint loads during bonobo locomotion: model predictions versus proxies

The analysis of internal trabecular and cortical bone has been an informative tool for drawing inferences about behaviour in extant and fossil primate taxa. Within the hand, metacarpal bone architecture has been shown to correlate well with primate locomotion; however, the extent of morphological differences across taxa is unexpectedly small given the variability in hand use. One explanation for this observation is that the activity-related differences in the joint loads acting on the bone are simply smaller than estimated based on commonly used proxies (i.e. external loading and joint posture), which neglect the influence of muscle forces. In this study, experimental data and a musculoskeletal finger model are used to test this hypothesis by comparing differences between climbing and knuckle-walking locomotion of captive bonobos ( Pan paniscus ) based on (i) joint load magnitude and direction predicted by the models and (ii) proxy estimations. The results showed that the activity-related differences in predicted joint loads are indeed much smaller than the proxies would suggest, with joint load magnitudes being almost identical between the two locomotor modes. Differences in joint load directions were smaller but still evident, indicating that joint load directions might be a more robust indicator of variation in hand use than joint load magnitudes. Overall, this study emphasizes the importance of including muscular forces in the interpretation of skeletal remains and promotes the use of musculoskeletal models for correct functional interpretations.

Locomotion Study of Bekantan (Nasalis larvatus)

The locomotion system in the primate is developed and diverged following the pressure of the environment. To survive, each species of primate will push their locomotor’s evolution to accommodate their foraging activities. Generally, the primate locomotion system is classified into vertical clinging and leaping (such as Tarsius), quadrupedalism (such as guenon), brachiation (such as gibbon), and bipedalism (human). Classification is usually based on the intermembral index, the ratio between the arm and leg length in percentage. The intermembral index of bekantan is about 90 on average; means the arm length is 90% of leg length. Based on the intermembral index, bekantan's locomotion system is hindlimb dominated gait and supposed to be quadrupedal terrestrial. However, in their natural habitat, bekantan spend their daily activities mostly on the trees. Terrestrial and arboreal movements were observed during foraging. Arboreal movements of bekantan are dominant where the forest canopy is remaining good. On the other hand, in open areas and where they have adapted to human existence, quadrupedal terrestrial behaviors will be dominant during foraging. Further observation in various areas is still needed to strengthen the type of locomotion system of bekantan.