Mikhail Kunin

Frequency-Velocity Mismatch: A Fundamental Abnormality in Parkinsonian Gait

Gait dysfunction and falling are major sources of disability for patients with advanced Parkinsons disease (PD). It is presently thought that the fundamental defect is an inability to generate normal stride length. Our data suggest, however, that the basic problem in PD gait is an impaired ability to match step frequency to walking velocity. In this study, foot movements of PD and normal subjects were monitored with an OPTOTRAK motion-detection system while they walked on a treadmill at different velocities. PD subjects were also paced with auditory stimuli at different frequencies. PD gait was characterized by step frequencies that were faster and stride lengths that were shorter than those of normal controls. At low walking velocities, PD stepping had a reduced or absent terminal toe lift, which truncated swing phases, producing shortened steps. Auditory pacing was not able to normalize step frequency at these lower velocities. Peak forward toe velocities increased with walking velocity and PD subjects could initiate appropriate foot dynamics during initial phases of the swing. They could not control the foot appropriately in terminal phases, however. Increased treadmill velocity, which matched the natural PD step frequency, generated a second toe lift, normalizing step size. Levodopa increased the bandwidth of step frequencies, but was not as effective as increases in walking velocity in normalizing gait. We postulate that the inability to control step frequency and adjust swing phase dynamics to slower walking velocities are major causes for the gait impairment in PD.

Three-dimensional kinematics and dynamics of the foot during walking: a model of central control mechanisms

The foot is a critical interface between the body and supporting surface during walking, but there is no coherent framework on which to model the dynamics of the stance and swing phases. To establish this framework, we studied the rotational and translational dynamics of foot movement in three dimensions with a motion detection system (OPTOTRAK), while subjects walked on a treadmill. Positions, velocities, and durations were normalized to leg-length and gravity. Foot position and rotation at toe-off were closely related to walking velocity. Foot pitch at toe clearance increased with walking velocity, but the medial–lateral and vertical toe positions were unaltered. Phase–plane trajectories along the fore-aft direction, i.e., plots of toe velocity versus position, were circular during the swing phases, with radii proportional to walking velocity. Peak forward, lateral, and upward velocities were linearly related to corresponding excursions, forming main sequences. A second order model predicted the changes in toe position and velocity, and the approximately hyperbolic decrements in duration as a function of walking velocity. The model indicates that the foot is controlled in an overdamped manner during the stance phase and as a feedback-controlled undamped pendulum during the swing. The data and model suggest that the state of the foot at toe-off, set by walking velocity during the stance phase, determines the dynamics of the swing phase. Thus, in addition to determining locomotion kinematics, walking velocity plays a critical role in determining the phase–plane trajectories and main sequence relationships of foot movements during the swing phases.

Head Stabilization by Vestibulocollic Reflexes During Quadrupedal Locomotion in Monkey

Little is known about the three-dimensional characteristics of vestibulocollic reflexes during natural locomotion. Here we determined how well head stability is maintained by the angular and linear vestibulocollic reflexes (aVCR, lVCR) during quadrupedal locomotion in rhesus and cynomolgus monkeys. Animals walked on a treadmill at velocities of 0.4-1.25 m/s. Head rotations were represented by Euler angles (Fick convention). The head oscillated in yaw and roll at stride frequencies (approximately 1-2 Hz) and pitched at step frequencies (approximately 2-4 Hz). Head angular accelerations (100-2,500 degrees/s2) were sufficient to have excited the aVOR to stabilize gaze. Pitch and roll head movements were <7 degrees , peak to peak, and the amplitude was unrelated to stride frequency. Yaw movements were larger due to spontaneous voluntary head shifts and were smaller at higher walking velocities. Head translations were small (< or =4 cm). Cynomolgus monkeys positioned their heads more forward in pitch than the rhesus monkeys. None of the animals maintained a forward head fixation point, indicating that the lVCR contributed little to compensatory head movements in these experiments. Significantly, aVCR gains in roll and pitch were close to unity and phases were approximately 180 degrees over the full frequency range of natural walking, which is in contrast to previous findings using anesthesia or passive trunk rotation with body restraint. We conclude that the behavioral state associated with active body motion is necessary to maintain head stability in pitch and roll over the full range of stride/step frequencies encountered during walking.

Motion sickness induced by off-vertical axis rotation (OVAR)

We tested the hypothesis that motion sickness is produced by an integration of the disparity between eye velocity and the yaw-axis orientation vector of velocity storage. Disparity was defined as the magnitude of the cross product between these two vectors. OVAR, which is known to produce motion sickness, generates horizontal eye velocity with a bias level related to velocity storage, as well as cyclic modulations due to re-orientation of the head re gravity. On average, the orientation vector is close to the spatial vertical. Thus, disparity can be related to the bias and tilt angle. Motion sickness sensitivity was defined as a ratio of maximum motion sickness score to the number of revolutions, allowing disparity and motion sickness sensitivity to be correlated. Nine subjects were rotated around axes tilted 10°–30° from the spatial vertical at 30°/s–120°/s. Motion sickness sensitivity increased monotonically with increases in the disparity due to changes in rotational velocity and tilt angle. Maximal motion sickness sensitivity and bias (6.8°/s) occurred when rotating at 60°/s about an axis tilted 30°. Modulations in eye velocity during OVAR were unrelated to motion sickness sensitivity. The data were predicted by a model incorporating an estimate of head velocity from otolith activation, which activated velocity storage, followed by an orientation disparity comparator that activated a motion sickness integrator. These results suggest that the sensory-motor conflict that produces motion sickness involves coding of the spatial vertical by the otolith organs and body tilt receptors and processing of eye velocity through velocity storage.

Towards a Methodology for Stabilizing the Gaze of a Quadrupedal Robot

When a quadrupedal robot moves, the body and head pitch, yaw and roll, because of its stepping. This natural effect of body and head motion adversely effects the use of visual sensors embedded in the robots head. Any object in the visual frame of the robot will, from the perspective of the robot, be subject to considerable unmodeled motion or slip. This problem does not affect mammals, which have vestibulo-collic and vestibulo-ocular reflexes that stabilize their gaze in space and maintain objects of interest approximately fixed on the retina. Our work is aimed towards constructing an artificial vestibular system for quadrupedal robots to maintain accurate gaze. This paper describes the first part of this work, wherein we have mounted an artificial vestibular system in a Sony aibo robot.

Effect of Canal Plugging on Quadrupedal Locomotion in Monkey

The vestibular system plays an important role in controling gait, but where in the labyrinths relevant activity arises is largely unknown. After the semicircular canals are plugged, low frequency (0.01–2 Hz) components of the angular vestibulo‐ocular reflex (aVOR) and angular vestibulo‐collic reflex (aVCR) are lost, but high frequency (3–20 Hz) components remain. We determined how loss of low frequency canal afference affects limb and head movements during quadrupedal locomotion. Head, body, and limb movements were recorded in three dimensions (3‐D) in a cynomolgus monkey with a motion detection system, while the animal walked on a treadmill. All six canals were plugged, reducing the canal time constants from ≈4.0 sec to ≈0.07 sec. Major changes in the control of the limbs occurred after surgery. Fore and hind limbs were held farther from the body, producing a broad‐based gait. Swing‐phase trajectories were inaccurate, and control of medial‐lateral limb movement was erratic. These changes in gait were present immediately after surgery, as well as 15 months later, when the animal had essentially recovered. Thus, control of the limbs in the horizontal plane was defective after loss of the low‐frequency semicircular canal input and never recovered. Cycle‐averaged pitch and roll head rotations, and 3‐D head translations were also significantly larger and more erratic after than before surgery. Head rotations in yaw could not be quantified due to intrusion of voluntary head turns. These findings indicate that the semicircular canals provide critical low frequency information to maximize the accuracy of stepping and stabilize the head during normal quadrupedal locomotion.

Reinforcement Learning Interfaces for Biomedical Database Systems

Studies of neural function that are carried out in different laboratories and that address different questions use a wide range of descriptors for data storage, depending on the laboratory and the individuals that input the data. A common approach to describe non-textual data that are referenced through a relational database is to use metadata descriptors. We have recently designed such a prototype system, but to maintain efficiency and a manageable metadata table, free formatted fields were designed as table entries. The database interface application utilizes an intelligent agent to improve integrity of operation. The purpose of this study was to investigate how reinforcement learning algorithms can assist the user in interacting with the database interface application that has been developed to improve the performance of the system

Managing a relational database with intelligent agents

A prototype relational database system was developed that has indexing capability, which threads into data acquisition and analysis programs used by a wide range of researchers. To streamline the user interface and table design, free-formatted table entries were used as descriptors for experiments. This approach potentially could increase data entry errors, compromising system index and retrieval capabilities. A methodology of integrating intelligent agents with the relational database was developed to cleanse and improve the data quality for search and retrieval. An intelligent agent was designed using JACK/sup /spl trade// (Agent Oriented Software Group) and integrated with an Oracle-based relational database. The system was tested by triggering agent corrective measures and was found to improve the quality of the data entries. Wider testing protocols and metrics for assessing its performance are subjects for future studies. This methodology for designing intelligent-based database systems should be useful in developing robust large-scale database systems.

Relational database linkage of scientific applications and their data files

Research in computational neuroscience has been following a model-based approach where data is comprised of digitized streams of sampled analog data, images and voice. The data are generally contained in files and specialized programs are used to analyze the data. In this study we developed a prototype system for indexing and retrieving information for use by an application that analyzes data. The data in the files consist of channels derived from analog and event driven sources. It is also linked to video images associated with the data acquisition. In this research, we developed an indexing capability that threads into the data acquisition and analysis programs to give the system a broad data base capability. We designed tables and relations within the database for indexing the files and information contained within the file. The system has the potential of giving us retrieval capabilities that include analog, event, and video data types.

Spatial orientation of caloric nystagmus.

Abstract: The spatial orientation of the slow‐phase eye velocity of caloric nystagmus was investigated in cynomolgus monkeys after all six semicircular canals had been plugged. Normal animals generate responses that have dominant convective components produced by movement of the endolymph in the lateral canal toward or away from gravity. As a result, the direction of horizontal slow‐phase velocity induced by cold‐water irrigation changes direction with changes in head position with regard to gravity. Plugging produced a dense overgrowth of bone that blocked the flow of endolymph, but the end organs were intact. Robust caloric nystagmus was elicited after recovery, but the horizontal (yaw) component was now always toward the stimulated (ipsilateral) side, regardless of head position re gravity. The induced caloric nystagmus had strong spatial orientation properties after canal plugging. With animals upright, the three‐dimensional velocity vector of the caloric nystagmus was close to the yaw axis with small vertical and roll components. Roll components became stronger in supine and prone positions and vertical components were enhanced in the right‐ and left‐side down positions. In each instance, the addition of the roll and vertical components moved the velocity vector of the nystagmus closer to the spatial vertical. Modeling supported the postulate that the caloric nystagmus after canal plugging is influenced by three factors: (1) a reduction in neural activity in the ampullary nerves on the stimulated side due to cooling of the nerves; (2) contraction of the endolymph in the closed space between the cupula and the plug due to cooling, which resulted in deflection of the cupula and hair cells toward the plug (ampullofugal deflection); and (3) alignment of eye velocity to gravity due to the orientation properties of velocity storage. Although convection is the most prominent factor in producing caloric responses in the normal state, our results suggest that alteration of nerve activity due to thermal effects, endolymph contraction or expansion, and velocity storage are also likely to contribute to the total response.