The migration pattern of cells during the mesoderm and endoderm differentiation from human pluripotent stem cells.

Gastrulation is the first major differentiation process in animal embryos. However, the dynamics of human gastrulation remain mostly unknown owing to the ethical limitations. We studied the dynamics of the mesoderm and endoderm cell differentiation from human pluripotent stem cells for insight into the cellular dynamics of human gastrulation. Human pluripotent stem cells have properties similar to those of the epiblast, which gives rise to the three germ layers. The mesoderm and endoderm were induced with more than 75% purity from human induced pluripotent stem cells. Single-cell dynamics of pluripotent stem cell-derived mesoderm and endoderm cells were traced using time-lapse imaging. Both mesoderm and endoderm cells migrate randomly, accompanied by short-term directional persistence. No substantial differences were detected between mesoderm and endoderm migration. Computer simulations created using the measured parameters revealed that random movement and external force, such as the spread out of cells from the primitive streak area, mimicked the homogeneous discoidal germ layer formation. These results were consistent with the development of amniotes, which suggests the effectiveness of human pluripotent stem cells as a good model for studying human embryogenesis.

Mixed-mode oscillations from a constrained extended Bonhoeffer-van der Pol oscillator with a diode.

An extended Bonhoeffer-van der Pol (BVP) oscillator is a circuit that is naturally extended to a three-variable system from a two-variable BVP oscillator. A BVP oscillator is known to exhibit a canard explosion, and the extended BVP oscillator generates mixed-mode oscillations (MMOs). In this work, we considered a case study where the nonlinear conductor in the extended BVP oscillator includes an idealized diode. The idealized case corresponds to a degenerate case where one of the parameters tends to infinity, and circuit dynamics are represented using a constrained equation, and at the expense of the model's naturalness, i.e., in a case in which the solutions of the dynamics are defined only forward in time, the Poincaré return maps are constructed as one-dimensional (1D). Using these 1D return maps, we explain various phenomena, such as simple MMOs and MMO-incrementing bifurcations. In this oscillator, there exists a small amplitude oscillation, which emerges as a consequence of supercritical Hopf bifurcation, and there exists large relaxation oscillation which appears via canard explosion by changing the bifurcation parameter. Between these small and large amplitude oscillations, the MMO bifurcations exhibit asymmetric Farey trees. Furthermore, these theoretical results were verified using laboratory measurements and experiments.

Relation between NIRS signal and motor capability.

Brain activities of three subjects performing a right-hand tapping task were measured by near-infrared spec-troscopy (NIRS). In experiments, the hemoglobin concentration change in the subjects' brains while they learned a new movement was analyzed. The results of these tests show that the channels covering the left primary motor cortex recorded a decreasing tendency in oxyHb when the subjects were repeating the tapping task. In contrast, the channels covering the supplementary motor cortex recorded an increasing tendency of oxyHb. These results suggest that the functional load on the brain decreases and the brain's active domain changes during motor learning.

Estimation of the direction of arm force by using NIRS signals.

In this study, we tried to discriminate the direction of arm force from hemoglobin concentration changes measured by near-infrared spectroscopy (NIRS). A self-organizing map (SOM) was used to classify the force direction information obtained from the NIRS signals. In a human subject experiment, the subjects were required to perform isometric arm movements in four directions. We investigated the feature quantities extracted from the time series data of the NIRS signals during the movement task. The feature vectors were used as the input vectors to the SOM. We tried to estimate the arm force direction by using a simple method based on the clusters given by the SOM. The results confirm that the direction of force is discriminable from the NIRS signal. In spite of the simple classification approach, the discrimination test yielded an average discrimination rate of 87.5 % for two directions. The experiment results suggest that NIRS signal must contain information related to the force directions.

Possibility of reinforcement learning based on event-related potential.

We applied event-related potential (ERP) to reinforcement signals that are equivalent to reward and punishment signals.We conducted an electroencephalogram (EEG) in which volunteers identified the success or failure of a task. We confirmed that there were differences in the EEG depending on whether the task was successful or not and suggested that ERP might be used as a reward of reinforcement leaning. We used a support vector machine (SVM) for recognizing the P300. We selected the feature vector in SVM that was composed of averages of each 50 ms for each of the six channels (C3,Cz,C4,P3,Pz,P4) for a total of 700 ms. We can suggest that reinforcement learning using P300 can be performed accurately.

Estimation of force motor command for NIRS-based BMI.

We consider a possibility for estimating EMG and force amplitude based on hemoglobin density. In experiments, subjects carried out isometric movements of three levels of force amplitude in order to measure EMG, force amplitude and hemoglobin density, and these relationships were investigated. We confirmed strong correlations between these measurements. From these relationships we propose two estimation models; one is to estimate the EMG from hemoglobin density and the other is to estimate the force amplitude from the estimated EMG. We can construct estimation models with high performance by minimizing AIC. Finally, we show an example of a BMI system applying estimation models to control an arm robot.

Application to robot control using brain function measurement by near-infrared spectroscopy.

In recent years, study of brain computer interface (BCI) is conducted actively and many researches of implementation using electro encephalic gram (EEG) are reported. On the other hand, some realization of BCI based on near-infrared spectroscopy (NIRS) also had been reported. Since a measurement instrument for NIRS is comparatively small-scale and it can perform noninvasive measurements, NIRS is expected as one of useful tool in order to realize versatile BCIs. In this paper, the estimation method is shown the possibility of applications to the ON/OFF control of BCI by NIRS. We measured regional cerebral blood flow during tapping movement of the right hand by NIRS and we propose a method to quantitatively estimate start and end timing of movement by using a neural network.

Movement time planning in human movement with via-points.

In previous research, even though various models that reproduce movement trajectory have already been proposed, a movement time planning criterion has never been proposed. However, a possible computational model that can estimate via-point time in complex trajectories has been proposed that suggests that the via-point time average of the integration of the square of the smoothness of the motor commands between each via-point is equal. In this report, we measured three kinds of via-point reaching movements and then performed statistical tests to investigate the computational theory. Results suggest that their computational theory is valid.

Can human isochrony be explained by a computational theory?

Previous studies on human motor control reported a phenomenon called isochrony, which is the compensatory increase of movement speed with increasing movement distance. On the other hand, in complex via-points trajectory formation, a possible computational model that can estimate via-point time has been proposed. This model is optimized on the condition that the Duration average of the Commanded Torque Change (DCTC) between each via-point is equal. In this paper, we consider the possibility that human isochrony can be explained by the computational theory and investigate the human drawing movement of a set of figure eight and double elliptical patterns. Results show that isochrony was observed in both duration and DCTC and that relative variance with an increasing movement perimeter ratio of DCTC was significantly less than duration. The possibility is suggested that human isochrony is a phenomenon observed as a result of movement time planning to equalize DCTC.