京都大学 / 新制・課程博士 / 博士(理学) / 甲第24465号 / 理博第4964号 / 新制||理||1709(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)准教授 平﨑 鋭矢, 教授 髙井 正成, 教授 今井 啓雄 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Differences between humans and extant apes in the pelvis and its key muscle attachment sites are thought to reflect a trade-off between arboreal and bipedal locomotor abilities. Human pelvic morphology enables the hamstrings to effectively power the hip hyperextension necessary for efficient bipedal locomotion, but this morphology is thought to reduce the capacity of these muscles to powerfully extend the hip when in a flexed position typical of arboreal locomotion. This research tested whether the enlarged human gluteus maximus may have been shaped by the continued importance of climbing among humans, as it has been suggested that it plays a compensatory role during powerful hip extension due to the reduced ability of the hamstrings. Musculoskeletal modeling and electromyography were used to assess the relative function of the gluteus maximus and the hamstrings in a human participant across two movement trials that required different amounts of hip extension: 1) bipedal walking, and 2) standing from a deep squat. It was hypothesized that the gluteus maximus would perform more effectively than the hamstrings to power hip extension from the flexed position of the squat. Differences in relative muscle activity across the two motions support this hypothesis in general, and implications for the evolutionary significance of the human gluteus maximus are that this muscle plays an important and likely compensatory role with the hamstrings during both standing up from a squat and bipedal walking. Results support the growing body of research that indicates that it is important to consider a broader range of human locomotive repertoires as of evolutionary significance, beyond solely terrestrial bipedal locomotion. / Graduate

Locomotion, the ability to walk freely in virtual environments, is a problem with no standardized solution. Walk-in-Place is one strand of solutions in which the user’s physical movement creates forward movement in the virtual environment. This technique is particularly useful for navigation in smartphone-based virtual reality without location detection. However, current mobile implementations use gaze-directed steering which limits the user’s ability to simultaneously scan the environment, which can reduce maneuverability. Additionally, step detection is triggered by head movement which shakes the head-mounted display and can therefore create discomfort and motion sickness. Detached Walk-in-place (dWIP) uses an external gyroscope attached to the body, or held in the hand, to track the user’s body rotation. This detaches the walking direction from gaze direction and removes step detection from the head-mounted-display. In this paper, I present a study of two different dWIP solutions (Torso- and Hand-directed). Both solutions are tested and compared with an existing mobile walk-in-place solution. Performance, user preference and simulator sickness were measured as the participants had to navigate a curved track using each method. The result shows that both dWIP methods required less steps compared with the current WIP, but the torso-directed dWIP is slower compared to the other two. There was no significant difference in user preference or simulator sickness. Overall, dWIP was well received and shows great potential as a mobile VR locomotion method. / Möjligheten att röra sig fritt i virtuella miljöer är ett problem utan en standardiserad lösning. Walk-in-place är en gren av lösningar som innebär att användarens fysiska rörelse skapar framåtrörelse i den virtuella miljön. Den här typen av lösning är speciellt användbar i smartphone-baserade virtuella miljöer utan platsregistrering. Nuvarande walk-in-place implementationer för smartphones använder huvudriktningen för styrning, vilket begränsar användarens förmåga att röra sig och samtidigt överblicka omgivningen, något som kan begränsa manövreringsförmågan. Dessutom triggas stegdetektering av huvudrörelser vilket kan skaka om headsetet och bidra till obehag och illamående. Frikopplad Walk-in-Place (dWIP) använder ett externt gyroskop som sätts fast på kroppen, eller hålls i handen, för att registrera användarens kroppsrotation. Detta frikopplar gångriktningen från huvudriktningen och tar bort stegdetekteringen från headsetet. I den här artikeln presenterar jag en studie av två olika dWIP-lösningar (Kropp- och Handriktad). Båda lösningarna är testade och jämförda med en existerade Walk-in-Place lösning för smartphones. Prestation, preferens och illamående mättes. Studiens deltagare navigerade igenom en böjd bana där de använde alla lösningarna varsin gång. Resultatet visar att deltagarna tog sig igenom banorna på färre steg med båda dWIP-lösningarna jämfört med den nuvarande WIP-lösningen, men att det tog längre tid med kroppsriktad dWIP. Det var ingen signifikant skillnad mellan deltagarnas preferenser eller upplevda illamående. Sammanfattningsvis blev dWIP väl mottaget av deltagarna och visade på en stor potential som navigationsmetod för VR till smartphones.

Rhythmic oscillations in neuronal activity display variations in amplitude (power) over a range of frequencies. Attention and cognitive performance correlate with increases in cortical gamma oscillations (40-70Hz) that are generated by the coordinated firing of glutamatergic pyramidal neurons and GABAergic interneurons, and are modulated by dopamine. In the medial prefrontal cortex (mPFC) of rats, gamma power increases during treadmill walking, or after administration of an acute subanesthetic dose of the NMDA receptor antagonist ketamine. Ketamine is also used to mimic symptoms of schizophrenia, including cognitive deficits, in healthy humans and rodents. Additionally, the ability of a drug to modify ketamine-induced gamma power has been proposed to predict its pro-cognitive therapeutic efficacy. However, the mechanism underlying ketamine-induced gamma oscillations is poorly understood. We hypothesized that gamma oscillations induced by walking and ketamine would be generated by a shared mechanism in the mPFC and one of its major sources of innervation, the mediodorsal thalamus (MD). Recordings from chronically implanted electrodes in rats showed that both treadmill walking and ketamine increased gamma power, firing rates, and spike-gamma LFP correlations in the mPFC. By contrast, in the MD, treadmill walking increased all three measures, but ketamine decreased firing rates and spike-gamma LFP correlations while increasing gamma power. Therefore, walking- and ketamine-induced gamma oscillations may arise from a shared circuit in the mPFC, but different circuits in the MD. Recent work in normal animals suggests that dopamine D4 receptors (D4Rs) synergize with the neuregulin/ErbB4 signaling pathway to modulate gamma oscillations and cognitive performance. Consequently, we hypothesized that drugs targeting the D4Rs and ErbB receptors would show pro-cognitive potential by reducing ketamine-induced gamma oscillations in mPFC. However, when injected before ketamine, neither the D4R agonist nor antagonist altered ketamine’s effects on gamma power or firing rates in the mPFC, but the pan-ErbB antagonist potentiated ketamine’s increase in gamma power, and prevented ketamine from increasing firing rates. This indicates that D4Rs and ErbB receptors influence gamma power via distinct mechanisms that interact with NMDA receptor antagonism differently. Our results highlight the value of using ketamine-induced changes in gamma power as a means of testing novel pharmaceutical agents.

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Running on land is fraught with challenges. Changes in topography, material properties, and the general heterogeneity of terrain necessitate the ability to sense, process, and compensate for changes quickly and repeatedly. Failure to do so successfully has potentially fatal consequences on an animal’s survival. I used lizards as an experimental model to examine how animals move successfully across complex terrain, because they are found in a vast range of habitat types and have a foot shape conserved across many families. I found that sprawled running appears to confer surprising robustness against large surface drops without any decrease in running speed, through the interplay between changes in body and limb posture. Increased combinations of foot placement and positioning result in more stable solutions than are otherwise possible among animals with erect limb postures. Using high-speed x-ray to visualize subsurface foot motion while running on sand, I discovered that lizards often found on fine sand spread their toes to distances known to maximize particle-particle interactions for force production on sand. Finally, I used a hopping robot outfitted with 3-D printed bio-inspired feet to show that the toe spacing pattern used by sand specialist lizards increases jump height for both stiff and flexible foot models. In summary, this work illuminates how adaptations for complex terrain may not be largely driven by selection for foot shape, but rather through modifications of behavior and functional morphology which likely confer robustness during locomotion across a variety of terrain. / Biology

Saber-toothed remains have been found worldwide throughout the Cenozoic, until the end of the Pleistocene. One site from Alachua County, Florida preserves a diverse Miocene fauna, including the machairodontine Nimravides galiani (Felidae) and the saber-toothed Barbourofelis loveorum (Barbourofelidae). Both taxa roamed what would become the Love Bone Bed site during the Late Miocene (Late Clarendonian NALMA), ~ 9.5 Mya. Previous descriptions focused on crania; yet the large sample of postcrania remained undescribed. Hence, this project includes a detailed postcranial description of both taxa. Results show that N. galiani resembles extant felids, whereas B. loveorum resembles Smilodon fatalis, as well as ursids. Additionally, locomotion and hunting behavior (prey capture) was examined quantitatively to assess ecologic overlap (niche partitioning vs direct competition). N. galiani probably displayed terrestrial locomotion in open habitats, whereas B. loveorum likely inhabited the deciduous forest as an ambulatory opportunistic/ambush predator. Results support niche partitioning, rather than direct competition.

Building an efficient and robust robot that does not use appendages for locomotion requires inspiration and a thorough understanding of the working principles of limbless animals’ locomotion. In these animals, the passive properties of their morphology and material allow them to dwell in complex terrains at different animals’ scales by using only a simple mode of locomotion, i.e., undulatory locomotion. A better understanding of these animals can inspire efficient locomotion strategies and lead to multi-gait terrain adaptation that exploits their physical intelligence. This study endeavors to model undulatory locomotion in various environments and study the effect of endogenous and exogenous dynamics in limbless bodies. First, undulatory locomotion is modeled analytically using the Lagrangian mechanics approach in a dry frictional environment. A discrete multi-bar system is set to get the propulsive force through frictional anisotropy. The system is then non-dimensionalized to determine the factors representing material and environmental properties. The principal components of the model are body stiffness, internal damping, moment of inertia, and frictional anisotropy. Simulations showed the interdependence of these quantities to achieve the desired speed. The results also highlighted the interdependence of endogenous and exogenous dynamics to achieve different locomotion gaits. Swimming, crawling, and polychaete-like locomotion are characterized based on stiffness factor, frictional factor, and frictional coefficient ratio. The model is validated by inputting the required parameters of the corn snake from the literature. Then undulatory locomotion is modeled in a viscous environment, and the results are compared with the dry environment. It is found that the optimum weight of dry and viscous frictional factors can be found in a hybrid environment to achieve better speed performance. Finally, the experimental validation is carried out in a dry friction environment. The results from experimental and physical models are compared. The physical robot is a wheel-based modular system with flexible joints moving on different substrates. The influence of the spatial distribution of the body stiffness on the speed performance is also explored. Findings suggest that the environment affects the performance of undulatory locomotion based on the body stiffness distribution. Although quantitatively the stiffness varies with the environment, we obtained a qualitative constitutive law for all environments. Specifically, we expect the stiffness distribution to exhibit either an ascending-descending or an ascending-plateau pattern along the length of the object, from head to tail. Furthermore, undulatory locomotion showed sensitivity to contact mechanics: solid-solid or solid-viscoelastic contact produced different locomotion dynamics. Our findings elucidate how terrestrial limbless animals achieve undulatory locomotion performance by exploiting the passive properties of the environment and the body. Application of the obtained results can lead to better-performing long-segmented robots exploiting the aptness of passive body dynamics and the characteristics of the environment where they need to move.

Assuming that the emergence of inside-out positional tracking in commercially available VR systems indicate a future where room-scale VR is experienced more freely, there is a demand for adaptable and immersive VR locomotion techniques that while enabling real walking overcomes the physical restrictions of a play space without the use of additional hardware. Hence, the purpose of this study was to explore the hypothesis that a subtle situation-based rotation of the immersive virtual environment (IVE) around the user can free up physically restricted virtual space and enable extended real walking in room-scale VR, while a full sense of presence is maintained. Based on Findings of a literature study, a prototype of an adaptable and mobile locomotion technique manipulating the IVE was developed and tested using three different rotations; a baseline medium rotation, a fast and a slow, all defined through trial and error with the capacities of freeing up restricted virtual space, and of maintaining presence, in mind. The user tests were designed as a within-subject test, aiming to expose the limits in the prototype by putting pressure on two potentially critical factors: user velocity and the capacity of freeing up restricted virtual space in all directions. The results imply that the proposed locomotion technique has the potential of extending virtual walking while maintaining a full sense of presence and that there is an optimally balanced rotation between the medium and slow rotation used in the present study. However, since the participants were not redirected enough to be preserved within the physical play space, the prototype may be used as a tool rather than as a redirecting technique. / Om man antar att utvecklingen och appliceringen av ”inside-out” positionsspårning i kommersiellt tillgängliga VR-system pekar på̊ en framtid där room-scale VR upplevs mer fritt, så Finns det ett behov av anpassningsbara VR-rörelsetekniker som utan extra hårdvara möjliggör ett större spelutrymme än det fysiska spelrummet samtidigt som användaren kan förflytta sig virtuellt genom verkliga rörelser. Syftet med denna studie var att utforska hypotesen att en subtil situationsbaserad rotation av den virtuella miljön runt användaren kan frigöra fysiskt begränsat virtuellt utrymme och samtidigt upprätthålla en känsla av full närvaro.  Baserat på resultaten från en litteraturstudie utvecklades en prototyp som och testades med tre olika hastigheter; medel, snabb och långsam. Dessa var alla definierade genom ”trial and error” baserat på prototypens kapacitet att frigöra begränsat virtuellt utrymme och att bibehålla närvaro i åtanke. Användartesterna utformades som ”within-subject” tester med målet att exponera prototypens begränsningar genom att pressa två potentiellt kritiska faktorer: hastigheten användaren rörde sig i och prototypens kapacitet att frigöra begränsat virtuellt utrymme i alla riktningar.  Resultaten antyder att den föreslagna rörelsetekniken har potentialen att möjliggöra ett större spelutrymme än det fysiska spelrummet samtidigt som en känsla av full närvaro upprätthålls och att det Finns en optimal rotation emellan rotationerna medel och långsam. Däremot, eftersom deltagarna inte omdirigerades tillräckligt för att bevaras inom det fysiska spelrummet är det troligt att prototypen borde användas som ett verktyg snarare än som en omdirigeringsteknik.

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