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Biomedical subjects

M Kawato

Publications and source records attributed to M Kawato.

At least 55 records · Page 3Linked to original sources
PubMed1995

Estimation of dynamic joint torques and trajectory formation from surface electromyography signals using a neural network model.

In this study, human arm movement was reconstructed from electromyography (EMG) signals using a forward dynamics model acquired by an artificial neural network within a modular architecture. Dynamic joint torques at the elbow and shoulder were estimated for movements in the horizontal plane from the surface EMG signals of 10 flexor and extensor muscles. Using only the initial conditions of the arm and the EMG time course as input, the network reliably reconstructed a variety of movement trajectories. The results demonstrate that posture maintenance and multijoint movements, entailing complex via-point specification and co-contraction of muscles, can be accurately computed from multiple surface EMG signals. In addition to the model's empirical uses, such as calculation of arm stiffness during motion, it allows evaluation of hypothesized computational mechanisms of the central nervous system such as virtual trajectory control and optimal trajectory planning.

Arm↗
PubMed1995

Internal representations of the motor apparatus: implications from generalization in visuomotor learning.

Recent computational studies have proposed that the motor system acquires internal models of kinematic transformations, dynamic transformations, or both by learning. Computationally, internal models can be characterized by 2 extreme representations: structured and tabular (C. G. Atkeson, 1989). Tabular models do not need prior knowledge about the structure of the motor apparatus, but they lack the capability to generalize learned movements. Structured models, on the other hand, can generalize learned movements, but they require an analytical description of the motor apparatus. In investigating humans' capacity to generalize kinematic transformations, we examined which type of representation humans' motor system might use. Results suggest that internal representations are nonstructured and nontabular. Findings may be due to a neural network model with a medium number of neurons and synapses.

Adult↗
PubMed1994

Ten-year survival and prognostic factors in multiple myeloma. Japan Myeloma Study Group.

Among 1119 Japanese patients with symptomatic multiple myeloma diagnosed between 1965 and 1981, 38 (3.4%) survived more than 10 years. Younger age, low tumour mass (absence of severe anaemia, hypercalcaemia, renal failure, and multiple bone lesions), low plasma cell percentage in bone marrow, mature and intermediate myeloma according to Greipp's criteria, and a positive response to subsequent treatment, were related to long-term survival according to univariate analysis. Multivariate logistic regression analysis indicated younger age and low tumour mass as pretreatment characteristics to be related to long-term survival. Prognostic factors proposed applicable to myeloma were also related to 10-year survival.

Aged↗
PubMed1994

Perceived motion in structure from motion: pointing responses to the axis of rotation.

We investigated the ability to match finger orientation to the direction of the axis of rotation in structure-from-motion displays. Preliminary experiments verified that subjects could accurately use the index finger to report direction. The remainder of the experiments studied the perception of the axis of rotation from full rotations of a group of discrete points, the profiles of a rotating ellipsoid, and two views of a group of discrete points. Subjects' responses were analyzed by decomposing the pointing responses into their slant and tilt components. Overall, the results indicated that subjects were sensitive to both slant and tilt. However, when the axis of rotation was near the viewing direction, subjects had difficulty reporting tilt with profiles and two views and showed a large bias in their slant judgments with two views and full rotations. These results are not entirely consistent with theoretical predictions. The results, particularly for two views, suggest that additional constraints are used by humans in the recovery of structure from motion.

Attention↗
PubMed1993

Inverse-dynamics model eye movement control by Purkinje cells in the cerebellum.

Many lines of evidence suggest that the cerebellum is involved in motor control. But what features of these movements are encoded by cerebellar neurons? For slow-tracking eye movements, the activity of Purkinje cells in the ventral paraflocculus of the cerebellum is known to be correlated with eye velocity and acceleration. Here we show that the complex temporal pattern of the firing frequency that occurs during the ocular following response elicited by movements of a large visual scene can be reconstructed by an inverse-dynamics representation, which uses the position, velocity and acceleration of eye movements. Further analysis reveals that the velocity and acceleration components can provide appropriate dynamic drive signals to ocular motor neurons, whereas the position component often has the wrong polarity. We conclude that these Purkinje cells primarily contribute dynamic command signals.

Action Potentials↗
PubMed1993

Virtual trajectory and stiffness ellipse during multijoint arm movement predicted by neural inverse models.

We predict the virtual trajectories and stiffness ellipses during multijoint arm movements by computer simulations. A two-link manipulator with four single-joint muscles and two double-joint muscles is used as a model of the human arm. Physical parameters of the model are derived from several experimental data. Among them, special emphasis is put on low values of the dynamic hand stiffness recently measured during single-joint and multijoint movements. The feedback-error-learning scheme to acquire the inverse dynamics model and the inverse statics model is utilized for this prediction. The virtual trajectories are much more complex than the actual trajectories. This indicates that planning the virtual trajectory is as difficult as solving the inverse dynamics problem for medium and fast movements, and simply falsifies the advocated computational advantage of the virtual trajectory control hypothesis. Thus, we conclude that learning inverse models is essential even in the virtual trajectory control framework. Finally, we propose a new computational model to learn the complicated shape of the virtual trajectories by integrating the virtual trajectory control and the feedback-error-learning scheme.

Arm↗
PubMed1992

A computational model of four regions of the cerebellum based on feedback-error learning.

We propose a computationally coherent model of cerebellar motor learning based on the feedback-error-learning scheme. We assume that climbing fiber responses represent motor-command errors generated by some of the premotor networks such as the feedback controllers at the spinal-, brain stem- and cerebral levels. Thus, in our model, climbing fiber responses are considered to convey motor errors in the motor-command coordinates rather than in the sensory coordinates. Based on the long-term depression in Purkinje cells each corticonuclear microcomplex in different regions of the cerebellum learns to execute predictive and coordinative control of different types of movements. Ultimately, it acquires an inverse model of a specific controlled object and complements crude control by the premotor networks. This general model is developed in detail as a specific neural circuit model for the lateral hemisphere. A new experiment is suggested to elucidate the coordinate frame in which climbing fiber responses are represented.

Animals↗
PubMed1992

Adaptive feedback control models of the vestibulocerebellum and spinocerebellum.

We extend the cerebellar learning model proposed by Kawato and Gomi (1992) to the case where a specific region of the cerebellum executes adaptive feedback control as well as feedforward control. The model is still based on the feedback-error-learning scheme. The proposed adaptive feedback control model is developed in detail as a specific neural circuit model for three different regions of the cerebellum and the learning of the corresponding representative movements: (i) the flocculus and adaptive modification of the vestibulo-ocular reflex and optokinetic eye-movement responses, (ii) the vermis and adaptive posture control, and (iii) the intermediate zones of the hemisphere and adaptive control of locomotion. As a representative example, simultaneous adaptation of the vestibulo-ocular reflex and the optokinetic eye-movement response was successfully simulated while the Purkinje cells receive copies of motor commands through recurrent neural connections as well as vestibular and retinal-slip parallel-fiber inputs.

Animals↗
PubMed1992

Chronic thyroiditis: thyroid function and histologic correlations in 601 cases.

Six hundred one patients with histologically proven "chronic thyroiditis" were assessed for the correlation of thyroid function to histologic findings. The histology of chronic thyroiditis was classified into four groups (oxyphilic, mixed, focal, and hyperplastic), and the thyroid function of patients was divided into hyperthyroid, euthyroid, latent hypothyroid, and overt hypothyroid, based on the laboratory data of serum triiodothyronine (T3), thyroxine (T4), and thyrotropin (TSH) levels, as well as thyrotropin-releasing hormone (TRH) tests. In the oxyphilic group (137 cases), 116 (85%) of the patients were classified as hypothyroid: 52 (38%) as latent hypothyroid and 64 (47%) as overt hypothyroid. In the mixed group (161 cases), the thyroid function of the patients varied. Thirty-seven (23%) of the patients were classified as hyperthyroid, 61 (39%) as euthyroid, 54 (33%) as latent hypothyroid, and nine (5%) as overt hypothyroid. In this group thyroid function was intimately related to the ratio of replacement by hyperplastic-changed follicles and oxyphilic-changed follicles. In the focal group (149 cases), 123 (83%) of the patients were classified as euthyroid, while 22 (14%) were classified as latent hypothyroid. The frequency of latent hypothyroid patients increased in parallel with the severity of cell infiltration. In the hyperplastic group (154 cases), 130 (85%) of the patients were classified as hyperthyroid. In this series 19 patients under 10 years of age were included, and no difference in the distribution of histologic varieties was observed between juvenile and adult patients. Thyroid needle biopsy is a useful and safe tool, not only for the histologic diagnosis of chronic thyroiditis, but also for the evaluation of thyroid function and the identification of causes for hyperthyroidism or hypothyroidism.

Adult↗
PubMed1992

The cerebellum and VOR/OKR learning models.

Although one particular model of the cerebellum, as proposed by Marr and Albus, provides a formal framework for understanding how heterosynaptic plasticity of Purkinje cells might be used for motor learning, the physiological details remain largely an engima. Developments in computational neuroscience and artificial neural networks applied to real control problems are essential to understand fully how workspace errors associated with movement performances can be converted into motor-command errors, and how these errors can then be used as one kind of synaptic input by motor-learning algorithms that are based on biologically plausible rules involving heterosynaptic plasticity. These developments, as well as recent advances in the study of cellular mechanisms of synaptic plasticity, form the basis for the detailed computational models of cerebellar motor learning that have been proposed. These models provide hints toward resolving a long-standing controversy in the oculomotor literature regarding the sites of adaptive changes in the vestibuloocular reflex (VOR) and the optokinetic eye movement response (OKR), and suggest new experiments to elucidate general mechanisms of sensory motor learning.

Animals↗
PubMed1990

Trajectory formation of arm movement by cascade neural network model based on minimum torque-change criterion.

We proposed that the trajectory followed by human subject arms tended to minimize the time integral of the square of the rate of change of torque (Uno et al. 1987). This minimum torque-change model predicted and reproduced human multi-joint movement data quite well (Uno et al. 1989). Here, we propose a neural network model for trajectory formation based on the minimum torque-change criterion. Basic ideas of information representation and algorithm are (i) spatial representation of time, (ii) learning of forward dynamics and kinetics model and (iii) relaxation computation based on the acquired model. The model can resolve ill-posed inverse kinematics and inverse dynamics problems for redundant controlled object as well as ill-posed trajectory formation problems. By computer simulation, we show that the model can produce a multi-joint arm trajectory while avoiding obstacles or passing through viapoints.

Algorithms↗
PubMed1989

Formation and control of optimal trajectory in human multijoint arm movement. Minimum torque-change model.

In this paper, we study trajectory planning and control in voluntary, human arm movements. When a hand is moved to a target, the central nervous system must select one specific trajectory among an infinite number of possible trajectories that lead to the target position. First, we discuss what criterion is adopted for trajectory determination. Several researchers measured the hand trajectories of skilled movements and found common invariant features. For example, when moving the hand between a pair of targets, subjects tended to generate roughly straight hand paths with bell-shaped speed profiles. On the basis of these observations and dynamic optimization theory, we propose a mathematical model which accounts for formation of hand trajectories. This model is formulated by defining an objective function, a measure of performance for any possible movement: square of the rate of change of torque integrated over the entire movement. That is, the objective function CT is defined as follows: (formula; see text) We overcome this difficult by developing an iterative scheme, with which the optimal trajectory and the associated motor command are simultaneously computed. To evaluate our model, human hand trajectories were experimentally measured under various behavioral situations. These results supported the idea that the human hand trajectory is planned and controlled in accordance with the minimum torque-change criterion.

Arm↗
PubMed1989

Disopyramide induces insulin secretion and plasma glucose diminution: studies using the in situ canine pancreas.

The mechanism of disopyramide-induced hypoglycemia, a life-threatening complication in the antiarrhythmic drug treatment, is still controversial. To elucidate this, we have evaluated plasma insulin (IRI) and glucagon (IRG) responses in the pancreatic vein (PV) of the in situ pancreas as well as responses of plasma IRI, IRG, and glucose in the femoral artery (FA) to disopyramide phosphate administration in anesthetized dogs. First, infusion of disopyramide at a dose of 50 mg for ten minutes directly into the pancreatic artery, but not the vehicle, increased significantly plasma IRI concentration in the PV (P less than .05 or less), where the IRI response started within three minutes and reached a peak of 2.8-fold preinfusion value at 30 minutes after starting the infusion (n = 7). Plasma IRI concentration in the FA also increased slightly but significantly (P less than .05). Plasma IRG concentration in the PV initially decreased significantly (P less than .05 or less) and in the FA at one point (P less than .05) during the infusion, and then increased significantly after cessation of the infusion, showing a peak of 1.9-fold preinfusion value at 60 minutes in the PV and the FA (P less than .05). Plasma glucose concentration in the FA decreased slowly and significantly after the infusion (P less than .05 or less) and fell by 16% of the baseline value at 60 minutes (P less than .05). Second, serum disopyramide concentration of 13.7 +/- 2.8 micrograms/mL at ten minutes, which corresponds to a twofold to threefold concentration of the human therapeutic level (n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Recent trends in the treatment and prognosis of adult leukemia with characteristics of patients in Japan: transition during the fifteen years from 1971 to 1985.

Patients with acute (2,569) and chronic (957) leukemia diagnosed at 19 institutes took part in the study on the "Multidisciplinary Treatment of Leukemia" between 1971 and 1985 and were investigated retrospectively. By dividing the 15 years into three five-year periods, we were able to compare patient ratios in the different periods. The proportions of acute to chronic leukemia cases showed no obvious change; however, the proportions of cases diagnosed as acute lymphocytic leukemia in acute leukemia showed a significant increase. The main chemotherapeutic drugs used during the three time periods were cytarabine or its analogues, the anthracyclines, 6-mercaputopurine and prednisolone, against acute myelogenous leukemia, and the vinca alkaloids, prednisolone and the anthracyclines against acute lymphocytic leukemia. The rate of complete remission from acute myelogenous leukemia made marked progress, from 45.1% during 1971-1975 to 62.3% during 1981-1985, but that of acute lymphocytic leukemia showed no significant progress, being 65% during 1971-1975 and 69.7% during 1981-1985. The durations of remission, however, and the survival times for patients with acute lymphocytic leukemia, as well as for those with acute myelogenous leukemia, became significantly longer over the three periods. Median survival times from chronic myelocytic leukemia were 37-40 mo in all three periods, showing no progress. There was a better prognosis in cases of chronic myelocytic leukemia with, than without, Philadelphia chromosome. Except for a low incidence of chronic lymphocytic leukemia in Japan, adult leukemia patients' characteristics and prognoses seem to be almost the same in Japan as in the U.S.A. and Europe.

Adolescent↗
PubMed1988

Coordinates transformation and learning control for visually-guided voluntary movement with iteration: a Newton-like method in a function space.

In order to control visually-guided voluntary movements, the central nervous system (CNS) must solve the following three computational problems at different levels: (1) determination of a desired trajectory in the visual coordinates, (2) transformation of the coordinates of the desired trajectory to the body coordinates and (3) generation of motor command. In this paper, the second and the third problems are treated at computational, representational and hardware levels of Marr. We first study the problems at the computational level, and then propose an iterative learning scheme as a possible algorithm. This is a trial and error type learning such as repetitive training of golf swing. The amount of motor command needed to coordinate activities of many muscles is not determined at once, but in a step-wise, trial and error fashion in the course of a set of repetitions. Actually, the motor command in the (n + 1)-th iteration is a sum of the motor command in the n-th iteration plus two modification terms which are, respectively, proportional to acceleration and speed errors between the desired trajectory and the realized trajectory in the n-th iteration. We mathematically formulate this iterative learning control as a Newton-like method in functional spaces and prove its convergence under appropriate mathematical conditions with use of dynamical system theory and functional analysis. Computer simulations of this iterative learning control of a robotic manipulator in the body or visual coordinates are shown. Finally, we propose that areas 2, 5, and 7 of the sensory association cortex are possible sites of this learning control. Further we propose neural network model which acquires transformation matrices from acceleration or velocity to motor command, which are used in these schemes.

Central Nervous System↗
PubMed1988

Histologic features of thyroid gland in a patient with bromide-induced hypothyroidism.

A case of a 22-year-old woman with bromide-induced hypothyroidism is presented. There have been no reports dealing with changes in thyroid function and thyroid morphologic characteristics associated with bromide intoxication. The characteristic histologic features of the affected thyroid gland included a marked hyperplasia of follicles lined by tall columnar follicular cells with foci of papillary proliferation and a loss of colloid materials in the follicular lumen. Ultrastructurally, thyroid follicular cells showed a marked dilatation of rough endoplasmic reticulum containing no electron-dense materials. X-ray microanalysis of the thyroid follicular cells revealed the presence of significant amounts of bromide and an absence of iodine. These indicated that severe hypothyroidism in this patient might be related to the accumulation of bromide in the thyroid follicular cells.

Adult↗