Biomedical subjects

Eishi Hirasaki

Publications and source records attributed to Eishi Hirasaki.

5 recordsLinked to original sources

PubMed2005

Instantaneous rotation axes during active head movements.

Rotation axes were calculated during active head movements using a motion analysis system. The mean rotation axis for 1 Hz head pitch when seated was posterior (6 mm) and inferior (21 mm) to the interaural axis, shifting 16 mm downwards when standing. During seated 2 Hz head pitch the rotation axis was close to the interaural axis, shifting downwards 15 mm when standing. This downward shift suggests that cervical vertebrae were recruited during head pitch with the trunk unsupported. The proximity of the pitch axis to the otoliths implies minimal otolith activation during small-amplitude, high-frequency pitch rotations, such as those encountered during locomotion. The mean rotation axis for 1 Hz yaw rotation was located slightly posterior (10 mm) to the interaural axis at the midpoint between the vestibular labyrinths when both seated and standing. In addition, the orientation of the plane of yaw rotation relative to the stereotaxic horizontal plane (pitched 5 degrees nose-down) was essentially fixed in head coordinates, regardless of the pitch orientation of the head, suggesting that yaw movements occur about an axis restricted by the mechanical structure of the atlanto-axial joint. The results demonstrate that the instantaneous rotation axes technique overcomes the inherent instability of the helical-axis representation for small head movements.

Adult↗

PubMed2004

Kinematic analysis of bipedal locomotion of a Japanese macaque that lost its forearms due to congenital malformation.

Spontaneously acquired bipedal locomotion of an untrained Japanese monkey (Macaca fuscata) is measured and compared with the elaborated bipedal locomotion of highly trained monkeys to assess the natural ability of a quadrupedal primate to walk bipedally. The subject acquired bipedalism by himself because of the loss of his forearms and hands due to congenital malformation. Two other subjects are performing monkeys that have been extensively trained for bipedal posture and locomotion. We videotaped their bipedal locomotion with two cameras in a lateral view and calculated joint angles (hip, knee, and ankle) and inertial angle of the trunk from the digitized joint positions. The results show that all joints are relatively more flexed in the untrained monkey. Moreover, it is noted that the ankle is less plantar flexed and the knee is more flexed in mid-to-late stance phase in the untrained monkey, suggesting that the trunk is not lifted up to store potential energy. In the trained monkeys, the joints are extended to bring the trunk as high as possible in the stance phase, and then stored potential energy is exchanged for kinetic energy to move forward. The efficient inverted pendulum mechanism seems to be absent in the untrained monkey's locomotion, implying that acquisition of such efficient bipedal locomotion is not a spontaneous ability for a Japanese monkey. Rather, it is probably a special skill that can only be acquired through artificial training for an inherently quadrupedal primate.

Animals↗

PubMed2004

Head movements during locomotion in a gibbon and Japanese macaques.

Kinematic analysis of head and body movements during locomotion in Macaca fuscata and Hylobates lar revealed that coordinated head rotation and translation that have been reported to play an important role in stabilizing gaze during locomotion for humans are also observed in non-human primates. The fact that well-coordinated head movements were observed in two species, and during both bipedal and quadrupedal walking, suggests that the head orientation during locomotion is well regulated in the manner of top-down control over the species and modes of locomotion. The result validates the monkey model and enables us to explore the underlying mechanisms for gaze, head, and postural control during locomotion.

Animals↗

PubMed2004

Do highly trained monkeys walk like humans? A kinematic study of bipedal locomotion in bipedally trained Japanese macaques.

In this study, we examined the kinematics of bipedal walking in macaque monkeys that have been highly trained to stand and walk bipedally, and compared them to the kinematics of bipedal walking in ordinary macaques. The results revealed that the trained macaques walked with longer and less frequent strides than ordinary subjects. In addition, they appear to have used inverted pendulum mechanics during bipedal walking, which resulted in an efficient exchange of potential and kinetic energy. These gait characteristics resulted from the relatively more extended hindlimb joints of the trained macaques. By contrast, the body of the ordinary macaques translated downward during the single-limb stance phase due to more flexed hindlimb joints. This resulted in almost in-phase fluctuations of potential and kinetic energy, which indicated that energy transformation was less efficient in the ordinary macaques. The findings provide two insights into the early stage of the evolution of human bipedalism. First, the finding that training considerably improved bipedal walking a posteriori may explain why the very first bipeds that might not yet have been morphologically adapted to bipedal walking continued to walk bipedally. The evolutionary transition from quadrupedalism to bipedalism might not be as difficult as has been envisioned. In addition, the finding that macaques, which are phylogenetically distant from humans and in which bipedal walking is unlike human walking, could develop humanlike gait characteristics with training, provides strong support for the commonly held but unproven idea that the characteristics of the human gait are advantageous to human bipedalism.

Animals↗

PubMed2002

Effects of caloric vestibular stimulation on head and trunk movements during walking.

The effects of vestibular stimulation on head and trunk movements were investigated during human walking (4.0 km/h). Vestibular stimulation was produced by irrigating an external auditory meatus with 4 degrees C ice water for 10 s. Using a 3-D motion analysis system, the linear (medial/lateral and vertical) translations and angular (yaw, pitch and roll) rotations were determined at the head, thorax, pelvis, knee, and foot. After caloric stimulation, waking trajectory deviated toward the stimulated side during dizziness. In addition, the amplitude of medial/lateral (M/L) linear translation and yaw rotation were significantly increased by caloric stimulation, especially at the head and thorax, whereas changes in vertical translation and pitch and roll rotations were not significant. The compensatory coordination (i.e., the yaw rotation to oppose the M/L linear translation) of the head was precisely maintained both before and after caloric stimulations, but it was decreased at the thorax and pelvis after stimulation. Our results suggested that vestibular sensory information, probably via the horizontal semicircular canals, contributes predominantly to the regulation of dynamic head and trunk movements in the M/L direction.

Adult↗