Forward dynamic simulation of Japanese macaque bipedal locomotion demonstrates better energetic economy in a virtualised plantigrade posture.

A plantigrade foot with a large robust calcaneus is regarded as a distinctive morphological feature of the human foot; it is presumably the result of adaptation for habitual bipedal locomotion. The foot of the Japanese macaque, on the other hand, does not have such a feature, which hampers it from making foot-ground contact at the heel during bipedal locomotion. Understanding how this morphological difference functionally affects the generation of bipedal locomotion is crucial for elucidating the evolution of human bipedalism. In this study, we constructed a forward dynamic simulation of bipedal locomotion in the Japanese macaque based on a neuromusculoskeletal model to evaluate how virtual manipulation of the foot structure from digitigrade to plantigrade affects the kinematics, dynamics, and energetics of bipedal locomotion in a nonhuman primate whose musculoskeletal anatomy is not adapted to bipedalism. The normal bipedal locomotion generated was in good agreement with that of actual Japanese macaques. If, as in human walking, the foot morphology was altered to allow heel contact, the vertical ground reaction force profile became double-peaked and the cost of transport decreased. These results suggest that evolutionary changes in the foot structure were important for the acquisition of human-like efficient bipedal locomotion.

Topographic distinction in long-term value signals between presumed dopamine neurons and presumed striatal projection neurons in behaving monkeys.

Nigrostriatal dopamine (DA) projections are anatomically organized along the dorsolateral-ventromedial axis, conveying long-term value signals to the striatum for shaping actions toward multiple future rewards. The present study examines whether the topographic organization of long-term value signals are observed upon activity of presumed DA neurons and presumed striatal projection neurons (phasically active neurons, PANs), as predicted based on anatomical literature. Our results indicate that DA neurons in the dorsolateral midbrain encode long-term value signals on a short timescale, while ventromedial midbrain DA neurons encode such signals on a relatively longer timescale. Activity of the PANs in the dorsal striatum is more heterogeneous for encoding long-term values, although significant differences in long-term value signals were observed between the caudate nucleus and putamen. These findings suggest that topographic DA signals for long-term values are not simply transferred to striatal neurons, possibly due to the contribution of other projections to the striatum.

Layer specificity of inputs from supplementary motor area and dorsal premotor cortex to primary motor cortex in macaque monkeys.

The primate frontal lobe processes diverse motor information in parallel through multiple motor-related areas. For example, the supplementary motor area (SMA) is mainly involved in internally-triggered movements, whereas the premotor cortex (PM) is highly responsible for externally-guided movements. The primary motor cortex (M1) deals with both aspects of movements to execute a single motor behavior. To elucidate how the cortical motor system is structured to process a variety of information, the laminar distribution patterns of signals were examined between SMA and M1, or PM and M1 in macaque monkeys by using dual anterograde tract-tracing. Dense terminal labeling was observed in layers 1 and upper 2/3 of M1 after one tracer injection into SMA, another tracer injection into the dorsal division of PM resulted in prominent labeling in the deeper portion of layer 2/3. Weaker labeling was also visible in layer 5 in both cases. On the other hand, inputs from M1 terminated in both the superficial and the deep layers of SMA and PM. The present data indicate that distinct types of motor information are arranged in M1 in a layer-specific fashion to be orchestrated through a microcircuit within M1.

Age-related changes in the cranial thickness of Japanese macaques ( Macaca fuscata ) / Cambios relacionados con la edad en el grosor craneal de los macacos japoneses ( Macaca fuscata )

Craniometry has revealed that continuous skull expansion occurs after dental maturity in macaques and other nonhuman primates. Endocranial volume has been shown to increase with age from mid-adulthood to older age in macaques. Thus, neurocranial thickness may decrease with age, especially from mid-adulthood to older age. Here, we investigated age-related changes in the cranial thickness of Japanese macaques (Macaca fuscata). Ten cranial thickness measurements (ten neurocranial landmarks) were made using computed tomographic scans of 140 crania from adult macaques (67 males and 73 females). The cranial thickness at many sites was shown to increase in the neurocranium from young adulthood (7-9 years) to early-mid adulthood (14-19 years) in males and latemid adulthood (19-24 years) in females, while it was decreased in the oldest age group (>24 years). The cranial thickness at various sites showed a significant decrease from mid-adulthood to very old age in both sexes, although females had more sites with decreasing thickness than did males. The difference between sexes in terms of age-related changes in cranial thickness at sites on the mid-sagittal plane may be associated with the differences in the size of the projecting face and canines between males and females. The greater number of sites with decreasing thickness in females than in males may be associated with postmenopausal estrogen depletion in female macaques.

La craneometría ha revelado que la expansión continua del cráneo se produce después de la madurez dental en macacos y otros primates no humanos. Se ha demostrado que el volumen endocraneal aumenta con la edad desde mediados de la edad adulta hasta la edad más avanzada en macacos. Por lo tanto, el grosor neurocraneal puede disminuir con la edad, especialmente desde la edad adulta media hasta la edad avanzada. Aquí, investigamos los cambios relacionados con la edad en el grosor craneal de los macacos Japoneses (Macaca fuscata). Se realizaron diez mediciones del grosor craneal (considerando diez puntos de referencia neurocraneales) mediante tomografías computarizadas de 140 cráneos de macacos adultos (67 machos y 73 hembras). Se observó que el grosor craneal en muchos sitios aumentó en el neurocráneo desde la edad adulta joven (7-9 años) hasta la edad adulta media (14-19 años) en los hombres y en la edad adulta media tardía (19-24 años) en las mujeres, mientras que se redujo en el grupo de mayor edad (> 24 años). El grosor craneal en varios sitios mostró una disminución significativa desde la edad adulta media hasta la edad muy avanzada en ambos sexos, aunque las hembras tenían más sitios con grosor decreciente. La diferencia entre sexos, en términos de cambios relacionados con la edad, en el grosor craneal en los sitios en el plano mediano puede asociarse con las diferencias en el tamaño de la cara y en los caninos entre machos y hembras. El mayor número de sitios con grosor decreciente en las hembras respecto a los machos puede estar asociado con el agotamiento de los estrógenos posmenopáusicos en los macacos hembras.

Muscle Spindle Density of Lateral Rotators of the Thigh in Japanese Macaques and a Gibbon.

We examined the six small lateral rotators of the hip joint, which is one of the most flexible joints and allows kinematically complex motions of the hindlimb, to elucidate the functional differentiation among these muscles and to test the hypothesis that species-specific characteristics in hindlimb use during locomotion are reflected in the muscle spindle density and in other parameters of the deep small hip joint rotators. For these purposes, we estimated the number of muscle spindles of the superior gemellus muscle (SG), inferior gemellus muscle, quadratus femoris muscle, obturator internus muscle (OI), obturator externus muscle, and piriformis muscle in three Japanese macaques and a gibbon, using 30-µm-thick serial sections throughout each muscle length after azan staining. The numbers of muscle spindles per 10,000 muscle fibers were determined to compare inter-muscle variation. The spindle density was highest in the SG and lowest in the OI in the Japanese macaques, suggesting that the SG, which is attached to the tendon of the OI, functions as a kinesiological monitor of the OI. On the other hand, SG the was missing in the gibbon, and the OI in the gibbon contained more spindles than that in the Japanese macaques. This suggests that the SG and the OI fused into one muscle in the gibbon. We postulate that the relative importance of the deep small hip rotator muscles differs between the Japanese macaques and gibbon and that the gibbon's muscles are less differentiated in terms of the spindle density, probably because this brachiating species uses its hindlimbs less frequently.