The right temporoparietal junction during a cooperation dilemma: An rTMS study

Cooperation enhances interpersonal communication and nurtures society. However, efforts to socially cooperate may often evoke conflict. Individuals may selfishly pursue a greater reward or success by exploiting the efforts of other individuals or taking unnecessary risk to oneself. Such a cooperation dilemma is highly prevalent in real life; thus, it has been studied in various disciplines. Although published functional magnetic resonance imaging studies have shown the involvement of the right temporoparietal junction (TPJ) in resolving a dilemma through cooperation, a causal relationship between the two has rarely been explored. Hence, we investigated this issue by combining repetitive transcranial magnetic stimulation with a priority game task (modified snowdrift game). In this game task, participants and opponent players jointly faced a problem whereby their collaboration was anticipated to defuse the situation. This conflicted with a choice in the participant's self-interest that was more rewarding but risky. We further included conditions with and without explicit social cues using figures describing elderly/pregnant passengers in the game opponent's car, and measured participants' prosocial traits to examine any cue-induced effect as well as the personality-cooperation relationship, respectively. The cooperation ratio was not statistically different in both the no-cue and with-cue conditions between the sham stimulation and inhibitory continuous theta burst stimulation (cTBS). However, after cTBS, in the no-cue condition, the strength of the association between cooperation ratio and empathy traits decreased significantly. These results add to our knowledge about the right TPJ's role in social cognition, which may be extraordinarily complex. This topic is deserving of further examination

Correlation between musculoskeletal structure of the hand and primate locomotion: Morphometric and mechanical analysis in prehension using the cross- and triple-ratios

Biometric ratios of the relative length of the rays in the hand have been analyzed between primate species in the light of their hand function or phylogeny. However, how relative lengths among phalanges are mechanically linked to the grasping function of primates with different locomotor behaviors remains unclear. To clarify this, we calculated cross and triple-ratios, which are related to the torque distribution, and the torque generation mode at different joint angles using the lengths of the phalanges and metacarpal bones in 52 primates belonging to 25 species. The torque exerted on the finger joint and traction force of the flexor tendons necessary for a cylindrical grip and a suspensory hand posture were calculated using the moment arm of flexor tendons measured on magnetic resonance images, and were compared among\ua0Hylobates\ua0spp.,\ua0Ateles\ua0sp., and\ua0Papio hamadryas. Finally, the torques calculated from the model were validated by a mechanical study detecting the force exerted on the phalanx by pulling the digital flexor muscles during suspension in these three species. Canonical discriminant analysis of cross and triple-ratios classified primates almost in accordance with their current classification based on locomotor behavior. The traction force was markedly reduced with flexion of the MCP joint parallel to the torque in brachiating primates; this was notably lower in the terrestrial quadrupedal primates than in the arboreal primates at mild flexion. Our mechanical study supported these features in the torque and traction force generation efficiencies. Our results suggest that suspensory or terrestrial quadrupedal primates have hand structures that can exert more torque at a suspensory posture, or palmigrade and digitigrade locomotion, respectively. Furthermore, our study suggests availability of the cross and triple-ratios as one of the indicators to estimate the hand function from the skeletal structure

Correlation between musculoskeletal structure of the hand and primate locomotion: Morphometric and mechanical analysis in prehension using the cross- and triple-ratios.

Biometric ratios of the relative length of the rays in the hand have been analyzed between primate species in the light of their hand function or phylogeny. However, how relative lengths among phalanges are mechanically linked to the grasping function of primates with different locomotor behaviors remains unclear. To clarify this, we calculated cross and triple-ratios, which are related to the torque distribution, and the torque generation mode at different joint angles using the lengths of the phalanges and metacarpal bones in 52 primates belonging to 25 species. The torque exerted on the finger joint and traction force of the flexor tendons necessary for a cylindrical grip and a suspensory hand posture were calculated using the moment arm of flexor tendons measured on magnetic resonance images, and were compared among Hylobates spp., Ateles sp., and Papio hamadryas. Finally, the torques calculated from the model were validated by a mechanical study detecting the force exerted on the phalanx by pulling the digital flexor muscles during suspension in these three species. Canonical discriminant analysis of cross and triple-ratios classified primates almost in accordance with their current classification based on locomotor behavior. The traction force was markedly reduced with flexion of the MCP joint parallel to the torque in brachiating primates; this was notably lower in the terrestrial quadrupedal primates than in the arboreal primates at mild flexion. Our mechanical study supported these features in the torque and traction force generation efficiencies. Our results suggest that suspensory or terrestrial quadrupedal primates have hand structures that can exert more torque at a suspensory posture, or palmigrade and digitigrade locomotion, respectively. Furthermore, our study suggests availability of the cross and triple-ratios as one of the indicators to estimate the hand function from the skeletal structure