16,052 research outputs found
The role of microtubule movement in bidirectional organelle transport
We study the role of microtubule movement in bidirectional organelle
transport in Drosophila S2 cells and show that EGFP-tagged peroxisomes in cells
serve as sensitive probes of motor induced, noisy cytoskeletal motions.
Multiple peroxisomes move in unison over large time windows and show
correlations with microtubule tip positions, indicating rapid microtubule
fluctuations in the longitudinal direction. We report the first high-resolution
measurement of longitudinal microtubule fluctuations performed by tracing such
pairs of co-moving peroxisomes. The resulting picture shows that
motor-dependent longitudinal microtubule oscillations contribute significantly
to cargo movement along microtubules. Thus, contrary to the conventional view,
organelle transport cannot be described solely in terms of cargo movement along
stationary microtubule tracks, but instead includes a strong contribution from
the movement of the tracks.Comment: 24 pages, 5 figure
New control strategies for neuroprosthetic systems
The availability of techniques to artificially excite paralyzed muscles opens enormous potential for restoring both upper and lower extremity movements with\ud
neuroprostheses. Neuroprostheses must stimulate muscle, and control and regulate the artificial movements produced. Control methods to accomplish these tasks include feedforward (open-loop), feedback, and adaptive control. Feedforward control requires a great deal of information about the biomechanical behavior of the limb. For the upper extremity, an artificial motor program was developed to provide such movement program input to a neuroprosthesis. In lower extremity control, one group achieved their best results by attempting to meet naturally perceived gait objectives rather than to follow an exact joint angle trajectory. Adaptive feedforward control, as implemented in the cycleto-cycle controller, gave good compensation for the gradual decrease in performance observed with open-loop control. A neural network controller was able to control its system to customize stimulation parameters in order to generate a desired output trajectory in a given individual and to maintain tracking performance in the presence of muscle fatigue. The authors believe that practical FNS control systems must\ud
exhibit many of these features of neurophysiological systems
Long-tail Behavior in Locomotion of Caenorhabditis elegans
The locomotion of Caenorhabditis elegans exhibits complex patterns. In
particular, the worm combines mildly curved runs and sharp turns to steer its
course. Both runs and sharp turns of various types are important components of
taxis behavior. The statistics of sharp turns have been intensively studied.
However, there have been few studies on runs, except for those on klinotaxis
(also called weathervane mechanism), in which the worm gradually curves toward
the direction with a high concentration of chemicals; this phenomenon was
discovered recently. We analyzed the data of runs by excluding sharp turns. We
show that the curving rate obeys long-tail distributions, which implies that
large curving rates are relatively frequent. This result holds true for
locomotion in environments both with and without a gradient of NaCl
concentration; it is independent of klinotaxis. We propose a phenomenological
computational model on the basis of a random walk with multiplicative noise.
The assumption of multiplicative noise posits that the fluctuation of the force
is proportional to the force exerted. The model reproduces the long-tail
property present in the experimental data.Comment: 30 pages, 11 figures, some errors were correcte
Dimensionality and dynamics in the behavior of C. elegans
A major challenge in analyzing animal behavior is to discover some underlying
simplicity in complex motor actions. Here we show that the space of shapes
adopted by the nematode C. elegans is surprisingly low dimensional, with just
four dimensions accounting for 95% of the shape variance, and we partially
reconstruct "equations of motion" for the dynamics in this space. These
dynamics have multiple attractors, and we find that the worm visits these in a
rapid and almost completely deterministic response to weak thermal stimuli.
Stimulus-dependent correlations among the different modes suggest that one can
generate more reliable behaviors by synchronizing stimuli to the state of the
worm in shape space. We confirm this prediction, effectively "steering" the
worm in real time.Comment: 9 pages, 6 figures, minor correction
Good vibrations: Guiding body movements with vibrotactile feedback
We describe the ongoing development of a system to support the teaching of good posture and bowing technique to novice violin players. Using an inertial motion capture system we can track in real-time a player’s bowing action and how it deviates from a target trajectory set by their music teacher. The system provides real-time vibrotactile feedback on the correctness of the student’s posture and bowing action. We present the findings of an initial study that shows that vibrotactile feedback can guide arm movements in one and two dimension pointing tasks. The advantages of vibrotactile feedback for teaching basic bowing technique to novice violin players are that it does not place demands on the students’ visual and auditory systems which are already heavily involved in the activity of music making, and is understood with little training
Analog VLSI-Based Modeling of the Primate Oculomotor System
One way to understand a neurobiological system is by building a simulacrum that replicates its behavior in real time using similar constraints. Analog very large-scale integrated (VLSI) electronic circuit technology provides such an enabling technology. We here describe a neuromorphic system that is part of a long-term effort to understand the primate oculomotor system. It requires both fast sensory processing and fast motor control to interact with the world. A one-dimensional hardware model of the primate eye has been built that simulates the physical dynamics of the biological system. It is driven by two different analog VLSI chips, one mimicking cortical visual processing for target selection and tracking and another modeling brain stem circuits that drive the eye muscles. Our oculomotor plant demonstrates both smooth pursuit movements, driven by a retinal velocity error signal, and saccadic eye movements, controlled by retinal position error, and can reproduce several behavioral, stimulation, lesion, and adaptation experiments performed on primates
A neural circuit for navigation inspired by C. elegans Chemotaxis
We develop an artificial neural circuit for contour tracking and navigation
inspired by the chemotaxis of the nematode Caenorhabditis elegans. In order to
harness the computational advantages spiking neural networks promise over their
non-spiking counterparts, we develop a network comprising 7-spiking neurons
with non-plastic synapses which we show is extremely robust in tracking a range
of concentrations. Our worm uses information regarding local temporal gradients
in sodium chloride concentration to decide the instantaneous path for foraging,
exploration and tracking. A key neuron pair in the C. elegans chemotaxis
network is the ASEL & ASER neuron pair, which capture the gradient of
concentration sensed by the worm in their graded membrane potentials. The
primary sensory neurons for our network are a pair of artificial spiking
neurons that function as gradient detectors whose design is adapted from a
computational model of the ASE neuron pair in C. elegans. Simulations show that
our worm is able to detect the set-point with approximately four times higher
probability than the optimal memoryless Levy foraging model. We also show that
our spiking neural network is much more efficient and noise-resilient while
navigating and tracking a contour, as compared to an equivalent non-spiking
network. We demonstrate that our model is extremely robust to noise and with
slight modifications can be used for other practical applications such as
obstacle avoidance. Our network model could also be extended for use in
three-dimensional contour tracking or obstacle avoidance
Dynamics and Stability of Low-Reynolds-Number Swimming Near a Wall
The locomotion of microorganisms and tiny artificial swimmers is governed by low-Reynolds-number
hydrodynamics, where viscous effects dominate and inertial effects are negligible. While the theory
of low-Reynolds-number locomotion is well studied for unbounded fluid domains, the presence of a
boundary has a significant influence on the swimmer’s trajectories and poses problems of dynamic
stability of its motion. In this paper we consider a simple theoretical model of a microswimmer near
a wall, study its dynamics, and analyze the stability of its motion. We highlight the underlying
geometric structure of the dynamics, and establish a relation between the reversing symmetry of
the system and existence and stability of periodic and steady solutions of motion near the wall.
The results are demonstrated by numerical simulations and validated by motion experiments with
macroscale robotic swimmer prototypes
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Towards a real-time system for teaching novices good violin bowing technique
We describe the ongoing development of a system to support the teaching of good posture and bowing technique to novice violin players. Using an inertial motion capture system we can track in real-time: i) a player’s bowing action (and measure how it deviates from a target trajectory); ii) whether the player is holding their violin correctly. We detail some initial experiments that show that vibrotactile feedback can guide arm movements in one and two dimensions. We then present some preliminary findings from integrating the motion capture and feedback components into a prototype real-time training system. The advantages of vibrotactile feedback are that: i) it does not use the students’ visual and auditory systems which are already involved in the activity of music making; ii) it is an intuitive way to guide body movements
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