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1.
Computational nature of human adaptive control during learning of reaching movements in force fields 总被引:7,自引:0,他引:7
Learning to make reaching movements in force fields was used as a paradigm to explore the system architecture of the biological
adaptive controller. We compared the performance of a number of candidate control systems that acted on a model of the neuromuscular
system of the human arm and asked how well the dynamics of the candidate system compared with the movement characteristics
of 16 subjects. We found that control via a supra-spinal system that utilized an adaptive inverse model resulted in dynamics
that were similar to that observed in our subjects, but lacked essential characteristics. These characteristics pointed to
a different architecture where descending commands were influenced by an adaptive forward model. However, we found that control
via a forward model alone also resulted in dynamics that did not match the behavior of the human arm. We considered a third
control architecture where a forward model was used in conjunction with an inverse model and found that the resulting dynamics
were remarkably similar to that observed in the experimental data. The essential property of this control architecture was
that it predicted a complex pattern of near-discontinuities in hand trajectory in the novel force field. A nearly identical
pattern was observed in our subjects, suggesting that generation of descending motor commands was likely through a control
system architecture that included both adaptive forward and inverse models. We found that as subjects learned to make reaching
movements, adaptation rates for the forward and inverse models could be independently estimated and the resulting changes
in performance of subjects from movement to movement could be accurately accounted for. Results suggested that the adaptation
of the forward model played a dominant role in the motor learning of subjects. After a period of consolidation, the rates
of adaptation in the internal models were significantly larger than those observed before the memory had consolidated. This
suggested that consolidation of motor memory coincided with freeing of certain computational resources for subsequent learning.
Received: 01 January 1998 / Accepted in revised form: 26 January 1999 相似文献
2.
Adaptive resonance theory (ART) demonstrates how the brain learns to recognize and categorize vast amounts of information
by using top–down expectations and attentional focusing. ART 3, one member of the ART family, embeds the computational properties
of the chemical synapse in its search process, but it converges slowly and is lack of stability when being applied in pattern
recognition and analysis. To overcome these problems, Nitric Oxide (NO), which serves as a newly discovered retrograde messenger
in Long-Term Potentiation (LTP), is introduced in retrograde adaptive resonance theory (ReART) model presented in this paper.
In the presented model a novel search hypothesis is proposed to incorporate angle and amplitude information of an external
input vector to decide whether the input matches the long-term memory (LTM) weights of an active node or not, and the embedded
NO retrograde mechanism makes the search procedure a closed loop, which improves the stability and convergence speed of the
transmitter releasing mechanism in a synapse. To make the model more adaptive and practical, a forgetting mechanism is built
to improve the weights updating process. Experimental results indicate that the proposed ReART model achieves low error rate,
fast convergence and self-organizing weights regulation.
Action Editor: Christiane Linster 相似文献
3.
Parkinson''s disease (PD) results in movement and sensory impairments that can be reduced by familiar music. At present, it is unclear whether the beneficial effects of music are limited to lessening the bradykinesia of whole body movement or whether beneficial effects also extend to skilled movements of PD subjects. This question was addressed in the present study in which control and PD subjects were given a skilled reaching task that was performed with and without accompanying preferred musical pieces. Eye movements and limb use were monitored with biomechanical measures and limb movements were additionally assessed using a previously described movement element scoring system. Preferred musical pieces did not lessen limb and hand movement impairments as assessed with either the biomechanical measures or movement element scoring. Nevertheless, the PD patients with more severe motor symptoms as assessed by Hoehn and Yahr (HY) scores displayed enhanced visual engagement of the target and this impairment was reduced during trials performed in association with accompanying preferred musical pieces. The results are discussed in relation to the idea that preferred musical pieces, although not generally beneficial in lessening skilled reaching impairments, may normalize the balance between visual and proprioceptive guidance of skilled reaching. 相似文献
4.
In motor tasks, errors between planned and actual movements generally result in adaptive changes which reduce the occurrence of similar errors in the future. It has commonly been assumed that the motor adaptation arising from an error occurring on a particular movement is specifically associated with the motion that was planned. Here we show that this is not the case. Instead, we demonstrate the binding of the adaptation arising from an error on a particular trial to the motion experienced on that same trial. The formation of this association means that future movements planned to resemble the motion experienced on a given trial benefit maximally from the adaptation arising from it. This reflects the idea that actual rather than planned motions are assigned 'credit' for motor errors because, in a computational sense, the maximal adaptive response would be associated with the condition credited with the error. We studied this process by examining the patterns of generalization associated with motor adaptation to novel dynamic environments during reaching arm movements in humans. We found that these patterns consistently matched those predicted by adaptation associated with the actual rather than the planned motion, with maximal generalization observed where actual motions were clustered. We followed up these findings by showing that a novel training procedure designed to leverage this newfound understanding of the binding of learning to action, can improve adaptation rates by greater than 50%. Our results provide a mechanistic framework for understanding the effects of partial assistance and error augmentation during neurologic rehabilitation, and they suggest ways to optimize their use. 相似文献
5.
Some characteristics of arm movements that humans exhibit during learning the dynamics of reaching are consistent with a
theoretical framework where training results in motor commands that are gradually modified to predict and compensate for novel
forces that may act on the hand. As a first approximation, the motor control system behaves as an adapting controller that
learns an internal model of the dynamics of the task. It approximates inverse dynamics and predicts motor commands that are
appropriate for a desired limb trajectory. However, we had previously noted that subtle motion characteristics observed during
changes in task dynamics challenged this simple model and raised the possibility that adaptation also involved sensory–motor
feedback pathways. These pathways reacted to sensory feedback during the course of the movement. Here we hypothesize that
adaptation to dynamics might also involve a modification of how the CNS responds to sensory feedback. We tested this through
experiments that quantified how the motor system's response to errors during voluntary movements changed as it adapted to
dynamics of a force field. We describe a nonlinear approach that approximates the impedance of the arm, i.e., force response
as a function of arm displacement trajectory. We observe that after adaptation, the impedance function changes in a way that
closely matches and counters the effect of the force field. This is particularly prominent in the long-latency (>100 ms) component
of response to perturbations. Therefore, it appears that practice not only modifies the internal model with which the brain
generates motor commands that initiate a movement, but also the internal model with which sensory feedback is integrated with
the ongoing descending commands in order to respond to error during the movement.
Received: 10 January 2001 / Accepted in revised form: 30 May 2001 相似文献
6.
Control of our movements is apparently facilitated by an adaptive internal model in the cerebellum. It was long thought that
this internal model implemented an adaptive inverse model and generated motor commands, but recently many reject that idea
in favor of a forward model hypothesis. In theory, the forward model predicts upcoming state during reaching movements so
the motor cortex can generate appropriate motor commands. Recent computational models of this process rely on the optimal
feedback control (OFC) framework of control theory. OFC is a powerful tool for describing motor control, it does not describe
adaptation. Some assume that adaptation of the forward model alone could explain motor adaptation, but this is widely understood
to be overly simplistic. However, an adaptive optimal controller is difficult to implement. A reasonable alternative is to
allow forward model adaptation to ‘re-tune’ the controller. Our simulations show that, as expected, forward model adaptation
alone does not produce optimal trajectories during reaching movements perturbed by force fields. However, they also show that
re-optimizing the controller from the forward model can be sub-optimal. This is because, in a system with state correlations
or redundancies, accurate prediction requires different information than optimal control. We find that adding noise to the
movements that matches noise found in human data is enough to overcome this problem. However, since the state space for control
of real movements is far more complex than in our simple simulations, the effects of correlations on re-adaptation of the
controller from the forward model cannot be overlooked. 相似文献
7.
The activity of motoneurons during motor patterns depends on their intrinsic properties and on synaptic inputs. This study
analyzed the properties of two leech motoneurons: the excitors of dorsal longitudinal muscles (DE-3) and of dorsal and ventral
longitudinal muscles (MN-L) in basal conditions (normal and high Mg2+ saline) and during crawling. The voltage–current relationships in DE-3 and MN-L were similar. The curves exhibited the largest
slope around resting potential, showed marked inward and outward rectification, and were not affected by high Mg2+. In response to 5-s pulses, DE-3 exhibited a fast initial adaptation, a slow recovery and a very slow late adaptation. High
Mg2+ abolished the initial high frequency. The frequency–voltage relationship for the rest of the response was highly similar
in normal and in high Mg2+ saline. MN-L exhibited a minor initial adaptation and then fired steadily. High Mg2+ diminished the frequency–voltage relationship. During crawling DE-3 and MN-L fired in phase and their frequency–voltage curves
overlapped with the lower end of the curves obtained in basal conditions. The results suggest that the activity of these motoneurons
during crawling was regulated, to a large extent, by synaptic inputs. 相似文献
8.
We review data showing that the cerebellum is required for adaptation of saccadic gain to repeated presentations of dual-step
visual targets and thus, presumably, for providing adaptive corrections for the brainstem saccade generator in response to
any error created by the open-loop saccadic system. We model the adaptability of the system in terms of plasticity of synapses
from parallel fibers to Purkinje cells in cerebellar cortex, stressing the integration of cerebellar cortex and nuclei in
microzones as the units for correction of motor pattern generators. We propose a model of the inferior olive as an error detector,
and use a ‘window of eligibility’ to insure that error signals that elicit a corrective movement are used to adjust the original
movement, not the secondary movement. In a companion paper we simulate this large, realistic network of neural-like units
to study the complex spatiotemporal behavior of neuronal subpopulations implicated in the control and adaptation of saccades.
Received: 25 November 1994/Accepted in revised form: 6 February 1996 相似文献
9.
Thomas Michelet Bernard Bioulac Dominique Guehl Michel Goillandeau Pierre Burbaud 《PloS one》2009,4(7)
Learning from mistakes is a key feature of human behavior. However, the mechanisms underlying short-term adaptation to erroneous action are still poorly understood. One possibility relies on the modulation of attentional systems after an error. To explore this possibility, we have designed a Stroop-like visuo-motor task in monkeys that favors incorrect action. Using this task, we previously found that single neurons recorded from the anterior cingulate cortex (ACC) were closely tuned to behavioral performance and, more particularly, that the activity of most neurons was biased towards the evaluation of erroneous action. Here we describe single neurons engaged in both error detection and response alertness processing, whose activation is closely associated with the improvement of subsequent behavioral performance. Specifically, we show that the effect of a warning stimulus on neuronal firing is enhanced after an erroneous response rather than a successful one and that this outcome is correlated with an error rate decrease. Our results suggest that the anterior cingulate cortex, which exhibits this activity, serves as a powerful computational locus for rapid behavioral adaptation. 相似文献
10.
Jayaraman R 《Journal of genetics》2011,90(2):383-391
Hypermutability is a phenotype characterized by a moderate to high elevation of spontaneous mutation rates and could result
from DNA replication errors, defects in error correction mechanisms and many other causes. The elevated mutation rates are
helpful to organisms to adapt to sudden and unforeseen threats to survival. At the same time hypermutability also leads to
the generation of many deleterious mutations which offset its adaptive value and therefore disadvantageous. Nevertheless,
it is very common in nature, especially among clinical isolates of pathogens. Hypermutability is inherited by indirect (second
order) selection along with the beneficial mutations generated. At large population sizes and high mutation rates many cells
in the population could concurrently acquire beneficial mutations of varying adaptive (fitness) values. These lineages compete
with the ancestral cells and also among themselves for fixation. The one with the ‘fittest’ mutation gets fixed ultimately
while the others are lost. This has been called ‘clonal interference’ which puts a speed limit on adaptation. The original
clonal interference hypothesis has been modified recently. Nonheritable (transient) hypermtability conferring significant
adaptive benefits also occur during stress response although its molecular basis remains controversial. The adaptive benefits
of heritable hypermutability are discussed with emphasis on host–pathogen interactions. 相似文献
11.
E. P. Poddubnaya 《Neurophysiology》2006,38(1):63-74
Based on the complex analysis of the data of cardiointervalographic (CIG) and rheoencephalographic (REG) examination of 37
healthy children and 63 children suffering from bronchial asthma (BA), we identified the most informative indices characterizing
reactions of the cardiovascular system under conditions of an active orthostatic test (coefficient of autonomic responsiveness
and index of responsiveness of the vessels). We conclude that the relation between the values of these indices allows one
to identify the level of strain of the regulatory mechanisms and the state of the adaptation systems of the organism, which
determine the adequacy of control of the autonomic sphere. The following gradations can be classified: an optimum level, compensated
adaptation disorders (strain and overstrain of the regulatory mechanisms), and decompensated adaptation disorders (exhaustion
of the regulatory mechanisms and failure of adaptation). Among clinically healthy children, we found a risk group (about 30%)
with manifestations of lowering of the organism’s adaptive abilities. It is shown that groups of healthy children and children
suffering from BA differ from each other in the shares of different patterns of EEG and variants of EEG responses to a hyperventilation
test. Qualitative and quantitative characteristics of EEG in children, despite high interindividual variability, clearly correlate
with the state of adaptation processes. The expedience of a complex approach in estimating the adaptation ability of the child
based on the data of CIG, REG and EEG examinations is discussed.
Neirofiziologiya/Neurophysiology, Vol. 38, No. 1, pp. 72–84, January–February, 2006. 相似文献
12.
Fransson PA Tjernström F Hafström A Magnusson M Johansson R 《Biological cybernetics》2002,86(5):355-365
The short-term (i.e., days) and long-term (i.e., months) effects of adaptation to posturography examinations were investigated
in 12 normal subjects who were repeatedly examined for five consecutive days and again after 90 days. The examinations were
conducted both with eyes open and closed, and the perturbations were evoked by a pseudorandomly applied vibration stimulation
to the calf muscles. The evoked anteroposterior responses were analyzed with a method considering adaptation in the slow changes
in posture and in the stimulus–response relationship. Repetition of examinations on a daily basis revealed a gradual improvement
of postural-control performance. The body sway induced by the stimulation was significantly reduced and the dynamical properties
changed. Most of the improvements remained after 90 days, but some parameters such as the complexity of the control system
used were increased to the initial level. The results confirm previous observations that postural control contains several
partially independent adaptive processes, observed in terms of alteration of posture and as a progressive reduction of body
sway induced by stimulation. The method used for the adaptation analysis in this study could be applied to analyze biological
systems with multiple individual adaptive processes with different time courses or characteristics, or where the adaptation
processes are related to multiple internal or external factors.
Received: 2 January 2001 / Accepted in revised form: 27 November 2001 相似文献
13.
During the procedure of prism adaptation, subjects execute pointing movements to visual targets under a lateral optical displacement: as consequence of the discrepancy between visual and proprioceptive inputs, their visuo-motor activity is characterized by pointing errors. The perception of such final errors triggers error-correction processes that eventually result into sensori-motor compensation, opposite to the prismatic displacement (i.e., after-effects). Here we tested whether the mere observation of erroneous pointing movements, similar to those executed during prism adaptation, is sufficient to produce adaptation-like after-effects. Neurotypical participants observed, from a first-person perspective, the examiner's arm making incorrect pointing movements that systematically overshot visual targets location to the right, thus simulating a rightward optical deviation. Three classical after-effect measures (proprioceptive, visual and visual-proprioceptive shift) were recorded before and after first-person's perspective observation of pointing errors. Results showed that mere visual exposure to an arm that systematically points on the right-side of a target (i.e., without error correction) produces a leftward after-effect, which mostly affects the observer's proprioceptive estimation of her body midline. In addition, being exposed to such a constant visual error induced in the observer the illusion "to feel" the seen movement. These findings indicate that it is possible to elicit sensori-motor after-effects by mere observation of movement errors. 相似文献
14.
Pedro Simões Marta Pascual Josiane Santos Michael R Rose Margarida Matos 《BMC evolutionary biology》2009,9(1):133-3
Here we present a correction to our article "Evolutionary dynamics of molecular markers during local adaptation: a case study
in Drosophila subobscura ". We have recently detected an error concerning the application of the Ln RH formula – a test to detect positive selection
– to our microsatellite data. Here we provide the corrected data and discuss its implications for our overall findings. The
corrections presented here have produced some changes relative to our previous results, namely in a locus (dsub14) that presents indications of being affected by positive selection. In general, our populations present less consistent indications
of positive selection for this particular locus in both periods studied – between generations 3 and 14 and between generation
14 and 40 of laboratory adaptation. Despite this, the main findings of our study regarding the possibility of positive selection
acting on that particular microsatellite still hold. As previously concluded in our article, further studies should be performed
on this specific microsatellite locus (and neighboring areas) to elucidate in greater detail the evolutionary forces acting
on this specific region of the O chromosome of Drosophila subobscura. 相似文献
15.
Gorban AN Pokidysheva LI Smirnova EV Tyukina TA 《Bulletin of mathematical biology》2011,73(9):2013-2044
The “Law of the Minimum” states that growth is controlled by the scarcest resource (limiting factor). This concept was originally
applied to plant or crop growth (Justus von Liebig, 1840, Salisbury, Plant physiology, 4th edn., Wadsworth, Belmont, 1992) and quantitatively supported by many experiments. Some generalizations based on more complicated “dose-response” curves
were proposed. Violations of this law in natural and experimental ecosystems were also reported. We study models of adaptation
in ensembles of similar organisms under load of environmental factors and prove that violation of Liebig’s law follows from
adaptation effects. If the fitness of an organism in a fixed environment satisfies the Law of the Minimum then adaptation
equalizes the pressure of essential factors and, therefore, acts against the Liebig’s law. This is the the Law of the Minimum paradox: if for a randomly chosen pair “organism–environment” the Law of the Minimum typically holds, then in a well-adapted system,
we have to expect violations of this law. 相似文献
16.
In many cases the distribution of saccadic reaction times (SRT) deviates considerably from a unimodal distribution and may
often exhibit several peaks. We present a statistical approach to determining the number and form of the individual peaks.
The overall density of the reaction times f
i
(t), i=1…M obtained in M different experiments with the same subject is described as the sum of K basis functions x
k
(t),k=1…K with different weights and an error term. A change in the experimental conditions is assumed to cause a change in the weights,
not in the basis functions. We minimize the square of the difference (measured data minus approximation), divided by the error
of the data. Incrementing K step by step we determine the necessary number of basis functions. This method is applied to data of six subjects tested
in different saccade tasks. We detect five different modes: two in the range 80–140 ms (express modes), two in the range 145–190 ms
(fast-regular mode) and one at about 230 ms (slow-regular mode). These modes are located at about the same positions for different
subjects. The method presented here not only proves statistically the existence of several modes in SRT distributions but
also allows the distributions to be described by a few characteristic numbers that go beyond the mean values and standard
deviations.
Received: 24 March 1997 / Accepted: 5 December 1997 相似文献
17.
Immunolocalization of tight junction proteins in blood vessels in human germinal matrix and cortex 总被引:2,自引:2,他引:0
Brain development occurs in a specialized environment maintained by a blood–brain barrier (BBB). An important structural element
of the BBB is the endothelial tight junction (TJ). TJs are present during the embryonic period, but BBB impermeability accrues
over an extended gestational interval. In studies of human premature infants, we used immunomicroscopy to determine if amounts
of the TJ proteins ZO-1, claudin and occludin increase with gestational age in vessels of germinal matrix (GM) and cortex.
By 24 weeks postconception (PC), TJ proteins were present in both GM and cortical vessels, but immunoreactivity in the GM
of the youngest subjects was less than in older subjects. At 24 weeks PC, TJ protein immunoreactivity in GM vessels was less
than in cortical vessels suggesting that TJ maturation progresses along a superficial to deep brain axis. This concept correlates
with conclusions from previous analyses of the expression of brain endothelial cell alkaline phosphatase (AP) activity. AP
appears in cortical vessels before appearing in deep white matter and GM vessels. Together, these data indicate that differentiation
of some functional specializations is still in progress in GM vessels during the third trimester. This maturation could relate
to the pathogenesis of germinal matrix hemorrhage–intraventricular hemorrhage. 相似文献
18.
A population level computational model of the basal ganglia that generates parkinsonian local field potential activity 总被引:1,自引:0,他引:1
George L. Tsirogiannis George A. Tagaris Damianos Sakas Konstantina S. Nikita 《Biological cybernetics》2010,102(2):155-176
Recordings from the basal ganglia’s subthalamic nucleus are acquired via microelectrodes immediately prior to the application
of Deep Brain Stimulation (DBS) treatment for Parkinson’s Disease (PD) to assist in the selection of the final point for the
implantation of the DBS electrode. The acquired recordings reveal a persistent characteristic beta band peak in the power
spectral density function of the Local Field Potential (LFP) signals. This peak is considered to lie at the core of the causality–effect
relationships of the parkinsonian pathophysiology. Based on LFPs acquired from human subjects during DBS for PD, we constructed
a computational model of the basal ganglia on the population level that generates LFPs to identify the critical pathophysiological
alterations that lead to the expression of the beta band peak. To this end, we used experimental data reporting that the strengths
of the synaptic connections are modified under dopamine depletion. The hypothesis that the altered dopaminergic modulation
may affect both the amplitude and the time course of the postsynaptic potentials is validated by the model. The results suggest
a pivotal role of both of these parameters to the pathophysiology of PD. 相似文献
19.
N. A. Prokopenko 《Neurophysiology》2012,43(6):487-493
We studied peculiarities of the autonomic reactions related to emotional experiences in persons with different characteristics
of their individuality. To model emotional states, tested subjects were proposed to mentally reproduce situations evoking
a sense of joy (positive emotions) and a feeling of grief (negative emotions). During such emotional tests, cardiointervalographic
(CIG) indices of the subjects were examined. The following properties of the individuality were taken into account: (i) extraversion/introversion
as the temperament parameter, (ii) externality/internality as a characteristic of the locus of psychological self-control,
and (iii) extrapunitivity/intropunitivity as a characterological feature manifested in frustration situations. Sympathico-parasympathic
influences were more powerful than central influences in regulation of the cardiorhythm in tested subjects with clearly “externally
directed” reactions to emotiogenic factors (extraverts, externals, and persons with an extrapunitive type of reaction). Vice versa, shifts of the autonomic balance toward activation of the sympathoadrenal link, relatively low efficacy of baroreflex regulation,
and strain of regulatory systems of the organism were observed at a high level of introversion in examined persons. Physiological
adaptation to the action of the various stressors, including the emotional ones, is realized mostly by the system cerebral
cortex – hypothalamus – hypophysis – adrenal cortex. In turn, the release of adrenalin by adrenal glands activates the reticular
formation and, via this structure, the hypothalamus and cerebral limbic system. Thus, it can be supposed that extraverts are
characterized by higher thresholds of the emotional sensitivity, which correspond to a higher threshold of activation of the
reticular formation and more intense inhibitory cortical influences upon subcortical formations. This is why extraverts manifest
weaker, in general, activation of the regulatory mechanisms of the cardiovascular system after the influence of extero- and
interoceptive stimuli, while in introverts such activation is more intense. 相似文献
20.
When each of many saccades is made to overshoot its target, amplitude gradually decreases in a form of motor learning called saccade adaptation. Overshoot is induced experimentally by a secondary, backwards intrasaccadic target step (ISS) triggered by the primary saccade. Surprisingly, however, no study has compared the effectiveness of different sizes of ISS in driving adaptation by systematically varying ISS amplitude across different sessions. Additionally, very few studies have examined the feasibility of adaptation with relatively small ISSs. In order to best understand saccade adaptation at a fundamental level, we addressed these two points in an experiment using a range of small, fixed ISS values (from 0° to 1° after a 10° primary target step). We found that significant adaptation occurred across subjects with an ISS as small as 0.25°. Interestingly, though only adaptation in response to 0.25° ISSs appeared to be complete (the magnitude of change in saccade amplitude was comparable to size of the ISS), further analysis revealed that a comparable proportion of the ISS was compensated for across conditions. Finally, we found that ISS size alone was sufficient to explain the magnitude of adaptation we observed; additional factors did not significantly improve explanatory power. Overall, our findings suggest that current assumptions regarding the computation of saccadic error may need to be revisited. 相似文献