Yifa Jiang

Impairment of spatial memory and changes in astroglial responsiveness following loss of molar teeth in aged SAMP8 mice

In order to evaluate the mechanism(s) responsible for senile impairment of cognitive function as a result of reduced mastication, the effects of the loss of the molar teeth (molarless condition) on the hippocampal expression of glial fibrous acidic protein (GFAP) and on spatial memory in young adult and aged SAMP8 mice were studied using immunohistochemical and behavioral techniques. Aged molarless mice showed a significantly reduced learning ability in a water maze test compared with age-matched control mice, while there was no difference between control and molarless young adult mice. Immunohistochemical analysis showed that the molarless condition enhanced the age-dependent increase in the density and hypertrophy of GFAP-labeled astrocytes in the CA1 region of the hippocampus. These effects increased the longer the molarless condition persisted. When the extracellular K+ concentration ([K+]o) was increased from 4 to 40 mM for hippocampal slices in vitro, the mean increase in the membrane potential was about 57 mV for fine, delicate astrocytes, the most frequently observed type of GFAP-positive cell in the young adult mice, and about 44 mV for the hypertrophic astrocytes of aged mice. However, there was no significant difference in resting membrane potential between these cell types. The data suggest that an impairment of spatial memory and changes in astroglial responsiveness occur following the loss of molar teeth in aged SAMP8 mice.

A PID Model of Balance Keeping Control and Its Application to Stability Assessment

The aim of this study is to establish a PID model of balance keeping control during static upright standing to elucidate the possible mechanism of body sway, and to apply this to balance stability assessment especially concerning the roles of pelvis and its muscles. The dynamic model includes five joints, i.e. two ankles, two hips and one lumbosacral joint makes up a multi-link system, and is driven by two pairs of muscles, the psoas major (PM) and glutaeus medius (GM). Ankle and lumbosacral joint sway in almost the same amplitude, whereas, their phase difference being approximately equal to pi. The result suggests that the trunk is maintaining its stance perpendicular to horizon. By applying human physical parameters to the model the body sways and its spectral response can be simulated. The simulated results are quite agree with the experimentally recorded both in body sway and in spectral response. It is suggest that balance keeping in upright standing can be fulfilled on this PID controller, and this model can be applied to individual body stability assessment

Balance-Keeping Control of Upright Standing in Biped Human Beings and its Application for Stability Assessment

1. Abstract One of the most important tasks in biped robot is the balance-keeping control. A question arisen as how do our human beings make the balance-keeping possible in upright standing as human beings are the only biped-walking primates, which takes several million years of evolution period to achieve this ability. Studies on humans’ balance-keeping mechanism are not only the work of physiologists but also a task of robot engineers since bio-mimetic approach is a shortcut for developing humanoid robot. This chapter will introduce some research progresses on balance-keeping control in upright standing. We will introduce the physical characteristics of human body at first, modeling the physical system of body, establishing a balance-keepin g control model, and at last applying the balance-keeping ability assessment for falls risk prediction. We wish those studies make contributions to robotics.

Analysis of regional brain activation during mastication by functional magnetic resonance imaging

Functional MRI was used to study the neural correlates for response selection and time adjustment for movement. The sub.jects performed a choice reaction time task while the randomness in response (order of stimulus presentation) and time (inter-stimulus intervul) were individually manipulated. lt was found that response uncertainty was associated with increased activation in the presupplementary motor area, while time uncertainty was associated with increased activation in the cerebellar posterior lobe. The double dissociation suggests anatomical segregation of “what to do” and “when to do” mechanisms in motor control. Additionally, the dorsal premotor cortex was shown to be active only when both response and time were uncertain, suggesting its role for integrating the two processes.