1,780 research outputs found
Maximization of Learning Speed in the Motor Cortex Due to Neuronal Redundancy
Many redundancies play functional roles in motor control and motor learning. For example, kinematic and muscle redundancies contribute to stabilizing posture and impedance control, respectively. Another redundancy is the number of neurons themselves; there are overwhelmingly more neurons than muscles, and many combinations of neural activation can generate identical muscle activity. The functional roles of this neuronal redundancy remains unknown. Analysis of a redundant neural network model makes it possible to investigate these functional roles while varying the number of model neurons and holding constant the number of output units. Our analysis reveals that learning speed reaches its maximum value if and only if the model includes sufficient neuronal redundancy. This analytical result does not depend on whether the distribution of the preferred direction is uniform or a skewed bimodal, both of which have been reported in neurophysiological studies. Neuronal redundancy maximizes learning speed, even if the neural network model includes recurrent connections, a nonlinear activation function, or nonlinear muscle units. Furthermore, our results do not rely on the shape of the generalization function. The results of this study suggest that one of the functional roles of neuronal redundancy is to maximize learning speed
On Neuromechanical Approaches for the Study of Biological Grasp and Manipulation
Biological and robotic grasp and manipulation are undeniably similar at the
level of mechanical task performance. However, their underlying fundamental
biological vs. engineering mechanisms are, by definition, dramatically
different and can even be antithetical. Even our approach to each is
diametrically opposite: inductive science for the study of biological systems
vs. engineering synthesis for the design and construction of robotic systems.
The past 20 years have seen several conceptual advances in both fields and the
quest to unify them. Chief among them is the reluctant recognition that their
underlying fundamental mechanisms may actually share limited common ground,
while exhibiting many fundamental differences. This recognition is particularly
liberating because it allows us to resolve and move beyond multiple paradoxes
and contradictions that arose from the initial reasonable assumption of a large
common ground. Here, we begin by introducing the perspective of neuromechanics,
which emphasizes that real-world behavior emerges from the intimate
interactions among the physical structure of the system, the mechanical
requirements of a task, the feasible neural control actions to produce it, and
the ability of the neuromuscular system to adapt through interactions with the
environment. This allows us to articulate a succinct overview of a few salient
conceptual paradoxes and contradictions regarding under-determined vs.
over-determined mechanics, under- vs. over-actuated control, prescribed vs.
emergent function, learning vs. implementation vs. adaptation, prescriptive vs.
descriptive synergies, and optimal vs. habitual performance. We conclude by
presenting open questions and suggesting directions for future research. We
hope this frank assessment of the state-of-the-art will encourage and guide
these communities to continue to interact and make progress in these important
areas
Aerospace medicine and biology: A continuing bibliography with indexes (supplement 333)
This bibliography lists 122 reports, articles and other documents introduced into the NASA Scientific and Technical Information System during January, 1990. Subject coverage includes: aerospace medicine and psychology, life support systems and controlled environments, safety equipment, exobiology and extraterrestrial life, and flight crew behavior and performance
Assistive telehealth systems for neurorehabilitation
Telehealth is an evolving field within the broader domain of Biomedical Engineering, specifically situated within the context of the Internet of Medical Things (IoMT). In today's society, the importance of Telehealth systems is increasingly recognized, as they enable remote patient treatment by physicians. One significant application in neurorehabilitation is Transcranial Direct Current Stimulation (tDCS), which has demonstrated its effectiveness in modulating mental function and learning over several years. Furthermore, tDCS is widely accepted as a safe approach in the field. This presentation focuses on the development of a non-invasive wearable tDCS device with integrated Internet connectivity. This IoMT device enables remote configuration of treatment parameters, such as session duration, current level, and placebo status. Clinicians can remotely access the device and define these parameters within the approved safety ranges for tDCS treatments. In addition to the wearable tDCS device, a prototype web portal is being developed to collect performance data during neurorehabilitation exercises conducted by individuals at home. This portal also facilitates remote interaction between patients and clinicians. To provide a platform-independent solution for accessing up-to-date healthcare information, a Progressive Web Application (PWA) is being developed. The PWA enables real-time communication between patients and doctors through text chat and video conferencing. The primary objective is to create a cross-platform web application with PWA features that can function effectively as a native application in various operating systems
Sensory coding in supragranular cells of the vibrissal cortex in anesthetized and awake mice
Sensory perception entails reliable representation of the
external stimuli as impulse activity of individual neurons (i.e.
spikes) and neuronal populations in the sensory area. An ongoing
challenge in neuroscience is to identify and characterize the
features of the stimuli which are relevant to a specific sensory
modality and neuronal strategies to effectively and efficiently
encode those features. It is widely hypothesized that the
neuronal populations employ “sparse coding” strategies to
optimize the stimulus representations with a low energetic cost
(i.e. low impulse activity). In the past two decades, a wealth of
experimental evidence has supported this hypothesis by showing
spatiotemporally sparse activity in sensory area. Despite
numerous studies, the extent of sparse coding and its underlying
mechanisms are not fully understood, especially in primary
vibrissal somatosensory cortex (vS1), which is a key model system
in sensory neuroscience. Importantly, it is not clear yet whether
sparse activation of supragranular vS1 is due to insufficient
synaptic input to the majority of the cells or the absence of
effective stimulus features.
In this thesis, first we asked how the choice of stimulus could
affect the degree of sparseness and/or the overall fraction of
the responsive vS1 neurons. We presented whisker deflections
spanning a broad range of intensities, including “standard
stimuli” and a high-velocity, “sharp” stimulus, which
simulated the fast slip events that occur during whisker mediated
object palpation. We used whole-cell and cell-attached recording
and calcium imaging to characterize the neuronal responses to
these stimuli. Consistent with previous literature, whole-cell
recording revealed a sparse response to the standard range of
velocities: although all recorded cells showed tuning to velocity
in their postsynaptic potentials, only a small fraction produced
stimulus-evoked spikes. In contrast, the sharp stimulus evoked
reliable spiking in a large fraction of regular spiking neurons
in the supragranular vS1. Spiking responses to the sharp stimulus
were binary and precisely timed, with minimum trial-to-trial
variability. Interestingly, we also observed that the sharp
stimulus produced a consistent and significant reduction in
action potential threshold.
In the second step we asked whether the stimulus dependent sparse
and dense activations we found in anesthetized condition would
generalize to the awake condition. We employed cell-attached
recordings in head-fixed awake mice to explore the degree of
sparseness in awake cortex. Although, stimuli delivered by a
piezo-electric actuator evoked significant response in a small
fraction of regular spiking supragranular neurons (16%-29%), we
observed that a majority of neurons (84%) were driven by manual
probing of whiskers. Our results demonstrate that despite sparse
activity, the majority of neurons in the superficial layers of
vS1 contribute to coding by representing a specific feature of
the tactile stimulus.
Thesis outline: Chapter 1 provides a review of the current
knowledge on sparse coding and an overview of the whisker-sensory
pathway. Chapter 2 represents our published results regarding
sparse and dense coding in vS1 of anesthetized mice
(Ranjbar-Slamloo and Arabzadeh 2017). Chapter 3 represents our
pending manuscript with results obtained with piezo and manual
stimulation in awake mice. Finally, in Chapter 4 we discuss and
conclude our findings in the context of the literature. The
appendix provides unpublished results related to Chapter 2. This
section is referenced in the final chapter for further
discussion
Adaptive Robotic Control Driven by a Versatile Spiking Cerebellar Network
The cerebellum is involved in a large number of different neural processes, especially in associative learning and in fine motor control. To develop a comprehensive theory of sensorimotor learning and control, it is crucial to determine the neural basis of coding and plasticity embedded into the cerebellar neural circuit and how they are translated into behavioral outcomes in learning paradigms. Learning has to be inferred from the interaction of an embodied system with its real environment, and the same cerebellar principles derived from cell physiology have to be able to drive a variety of tasks of different nature, calling for complex timing and movement patterns. We have coupled a realistic cerebellar spiking neural network (SNN) with a real robot and challenged it in multiple diverse sensorimotor tasks. Encoding and decoding strategies based on neuronal firing rates were applied. Adaptive motor control protocols with acquisition and extinction phases have been designed and tested, including an associative Pavlovian task (Eye blinking classical conditioning), a vestibulo-ocular task and a perturbed arm reaching task operating in closed-loop. The SNN processed in real-time mossy fiber inputs as arbitrary contextual signals, irrespective of whether they conveyed a tone, a vestibular stimulus or the position of a limb. A bidirectional long-term plasticity rule implemented at parallel fibers-Purkinje cell synapses modulated the output activity in the deep cerebellar nuclei. In all tasks, the neurorobot learned to adjust timing and gain of the motor responses by tuning its output discharge. It succeeded in reproducing how human biological systems acquire, extinguish and express knowledge of a noisy and changing world. By varying stimuli and perturbations patterns, real-time control robustness and generalizability were validated. The implicit spiking dynamics of the cerebellar model fulfill timing, prediction and learning functions.European Union (Human Brain Project)
REALNET FP7-ICT270434
CEREBNET FP7-ITN238686
HBP-60410
The role of noise in sensorimotor control
Goal-directed arm movements show stereotypical trajectories, despite the infinite possible ways to reach a given end point. This thesis examines the hypothesis that this stereotypy arises because movements are optimised to reduce the consequences of signal-dependent noise on the motor command. Both experimental and modelling studies demonstrate that signal-dependent noise arises from the normal behaviour of the muscle and motor neuron pool, and has a particular distribution across muscles of different sizes. Specifically, noise decreases in a systematic fashion with increasing muscle strength and motor unit number. Simulations of obstacle avoidance performance in the presence of signal-dependent noise demonstrate that the optimal trajectory for reaching the target accurately and without collision matches the observed trajectories. Isometric force generation is also shown to have systematic changes in variability with posture, which can be explained by the presence of signal-dependent noise in the muscles of the arm. These results confirm the tested hypothesis and imply that consideration of the statistics of action is crucial to human movement planning. To investigate the importance of feedback in the motor system, the impact of static position on motor excitability was examined using transcranial magnetic stimulation and systematic changes in motor evoked potentials were observed. Force generated at the wrist following stimulation was analysed in terms of different possible movement representations, and the differences between force fields arising from stimulation over the cervical spinal cord and from stimulation over primary motor cortex are determined. These results demonstrate the structured influence of proprioceptive feedback on the human motor system. All the experiments are discussed in relation to current theories describing the control of human movements and the impact of noise in the motor system
Brain-Inspired Computational Intelligence via Predictive Coding
Artificial intelligence (AI) is rapidly becoming one of the key technologies
of this century. The majority of results in AI thus far have been achieved
using deep neural networks trained with the error backpropagation learning
algorithm. However, the ubiquitous adoption of this approach has highlighted
some important limitations such as substantial computational cost, difficulty
in quantifying uncertainty, lack of robustness, unreliability, and biological
implausibility. It is possible that addressing these limitations may require
schemes that are inspired and guided by neuroscience theories. One such theory,
called predictive coding (PC), has shown promising performance in machine
intelligence tasks, exhibiting exciting properties that make it potentially
valuable for the machine learning community: PC can model information
processing in different brain areas, can be used in cognitive control and
robotics, and has a solid mathematical grounding in variational inference,
offering a powerful inversion scheme for a specific class of continuous-state
generative models. With the hope of foregrounding research in this direction,
we survey the literature that has contributed to this perspective, highlighting
the many ways that PC might play a role in the future of machine learning and
computational intelligence at large.Comment: 37 Pages, 9 Figure
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