Slow Adaptation Process Research Articles

Early-Stage Alzheimer's Disease Affects Fast But Not Slow Adaptive Processes in Motor Learning.

Alzheimer's disease (AD) is characterized by an initial decline in declarative memory, while nondeclarative memory processing remains relatively intact. Error-based motor adaptation is traditionally seen as a form of nondeclarative memory, but recent findings suggest that it involves both fast, declarative, and slow, nondeclarative adaptive processes. If the declarative memory system shares resources with the fast process in motor adaptation, it can be hypothesized that the fast, but not the slow, process is disturbed in AD patients. To test this, we studied 20 early-stage AD patients and 21 age-matched controls of both sexes using a reach adaptation paradigm that relies on spontaneous recovery after sequential exposure to opposing force fields. Adaptation was measured using error clamps and expressed as an adaptation index (AI). Although patients with AD showed slightly lower adaptation to the force field than the controls, both groups demonstrated effects of spontaneous recovery. The time course of the AI was fitted by a hierarchical Bayesian two-state model in which each dynamic state is characterized by a retention and learning rate. Compared to controls, the retention rate of the fast process was the only parameter that was significantly different (lower) in the AD patients, confirming that the memory of the declarative, fast process is disturbed by AD. The slow adaptive process was virtually unaffected. Since the slow process learns only weakly from an error, our results provide neurocomputational evidence for the clinical practice of errorless learning of everyday tasks in people with dementia.

Task space exploration improves adaptation after incompatible virtual surgeries.

Humans have a remarkable capacity to learn new motor skills, a process that requires novel muscle activity patterns. Muscle synergies may simplify the generation of muscle patterns through the selection of a small number of synergy combinations. Learning of new motor skills may then be achieved by acquiring novel muscle synergies. In a previous study, we used myoelectric control to construct virtual surgeries that altered the mapping from muscle activity to cursor movements. After compatible virtual surgeries, which could be compensated by recombining subject-specific muscle synergies, participants adapted quickly. In contrast, after incompatible virtual surgeries, which could not be compensated by recombining existing synergies, participants explored new muscle patterns but failed to adapt. Here, we tested whether task space exploration can promote learning of novel muscle synergies required to overcome an incompatible surgery. Participants performed the same reaching task as in our previous study but with more time to complete each trial, thus allowing for exploration. We found an improvement in trial success after incompatible virtual surgeries. Remarkably, improvements in movement direction accuracy after incompatible surgeries occurred faster for corrective movements than for the initial movement, suggesting that learning of new synergies is more effective when used for feedback control. Moreover, reaction time was significantly higher after incompatible than compatible virtual surgeries, suggesting an increased use of an explicit adaptive strategy to overcome incompatible surgeries. Taken together, these results indicate that exploration is important for skill learning and suggest that human participants, with sufficient time, can learn new muscle synergies.NEW & NOTEWORTHY Motor skill learning requires the acquisition of novel muscle patterns, a slow adaptive process. Here we show that learning to control a cursor after an incompatible virtual surgery, a complex skill requiring new muscle synergies, is possible when enough time for task space exploration is provided. Our results suggest that learning new synergies is related to the exceptional human capacity to acquire a wide variety of novel motor skills with practice.

Robust point-process Granger causality analysis in presence of exogenous temporal modulations and trial-by-trial variability in spike trains.

Assessing directional influences between neurons is instrumental to understand how brain circuits process information. To this end, Granger causality, a technique originally developed for time-continuous signals, has been extended to discrete spike trains. A fundamental assumption of this technique is that the temporal evolution of neuronal responses must be due only to endogenous interactions between recorded units, including self-interactions. This assumption is however rarely met in neurophysiological studies, where the response of each neuron is modulated by other exogenous causes such as, for example, other unobserved units or slow adaptation processes. Here, we propose a novel point-process Granger causality technique that is robust with respect to the two most common exogenous modulations observed in real neuronal responses: within-trial temporal variations in spiking rate and between-trial variability in their magnitudes. This novel method works by explicitly including both types of modulations into the generalized linear model of the neuronal conditional intensity function (CIF). We then assess the causal influence of neuron i onto neuron j by measuring the relative reduction of neuron j's point process likelihood obtained considering or removing neuron i. CIF's hyper-parameters are set on a per-neuron basis by minimizing Akaike's information criterion. In synthetic data sets, generated by means of random processes or networks of integrate-and-fire units, the proposed method recovered with high accuracy, sensitivity and robustness the underlying ground-truth connectivity pattern. Application of presently available point-process Granger causality techniques produced instead a significant number of false positive connections. In real spiking responses recorded from neurons in the monkey pre-motor cortex (area F5), our method revealed many causal relationships between neurons as well as the temporal structure of their interactions. Given its robustness our method can be effectively applied to real neuronal data. Furthermore, its explicit estimate of the effects of unobserved causes on the recorded neuronal firing patterns can help decomposing their temporal variations into endogenous and exogenous components.

Slow Temporal Dynamics of Motion-Induced Brightness Shift Reveals Impact of Adaptation.

Brightness of an object is determined by various factors including ambient illumination, surface reflectance of the object, and spatial and temporal relation between the object and its surrounding context. Recently, it has been demonstrated that the motion of an object alters its own and nearby object's appearance such as brightness and color. This study aims to unveil mechanisms of the motion-induced brightness shift by measuring its temporal dynamics. We found that the motion-induced brightness shift occurred instantaneously with the motion onset when the motion was introduced abruptly. However, the brightness of a stationary object was altered gradually by a nearby moving object in about 2 s time window when the stationary dot was introduced abruptly. Two distinct temporal dynamics (slow vs. fast) of the motion-induced brightness shift demonstrate that both slow neural adaptation and fast neural normalization processes determine the brightness shift induced by the object's motion.

INOCULUM ADAPTATION FOR THE ANAEROBIC DIGESTION OF MEZCAL VINASSES

Vinasses are a very harmful residue of the alcohol distillation, their discharge into soil and water can cause negative environmental impacts if the appropriate treatments do not take place. Anaerobic digestion has shown to be the best technological and economical method to treat this residue, thus bioenergy can be generated as by-product of this process. Nevertheless, the slow adaptation of the microbial consortium in inoculum (activated sludge) to the substrate (mezcal vinasses) is very important to enhance the efficiency of the biogas and methane production, as well as organic matter removal. In this work, the adaptation process of the anaerobic digestion of mezcal vinasses was carried out in a 30-day period. Inoculum (activates sludge) and vinasses were mixed initially at the ratio 7:3. The feeding steps were done every seven days replacing 30 % of the total volume with new vinasses. Biogas was quantified and qualified. Biogas production reached 217 L/kgVSvinassesgenerating a daily methane content between 50 and 55 % by the end of the adaptation period. The organic matter removal efficiency was almost seven times higher at the end of the adaptation, in comparison to the beginning. This suggests that a slow adaptation process enhance the organic matter removal and eventually other pollutants in vinasses. When comparing this results with the literature, biogas and methane production were similar, nevertheless the anaerobic digestion could be optimized, in order to increase the methane content in biogas and the removal rate of organic matter.

Both fast and slow learning processes contribute to savings following sensorimotor adaptation

Recent work suggests that the rate of learning in sensorimotor adaptation is likely not fixed, but rather can change based on previous experience. One example is savings, a commonly observed phenomenon whereby the relearning of a motor skill is faster than the initial learning. Sensorimotor adaptation is thought to be driven by sensory prediction errors, which are the result of a mismatch between predicted and actual sensory consequences. It has been proposed that during motor adaptation the generation of sensory prediction errors engages two processes (fast and slow) that differ in learning and retention rates. We tested the idea that a history of errors would influence both the fast and slow processes during savings. Participants were asked to perform the same force field adaptation task twice in succession. We found that adaptation to the force field a second time led to increases in estimated learning rates for both fast and slow processes. While it has been proposed that savings is explained by an increase in learning rate for the fast process, here we observed that the slow process also contributes to savings. Our work suggests that fast and slow adaptation processes are both responsive to a history of error and both contribute to savings. NEW & NOTEWORTHY We studied the underlying mechanisms of savings during motor adaptation. Using a two-state model to represent fast and slow processes that contribute to motor adaptation, we found that a history of error modulates performance in both processes. While previous research has attributed savings to only changes in the fast process, we demonstrated that an increase in both processes is needed to account for the measured behavioral data.

Fast reversible learning based on neurons functioning as anisotropic multiplex hubs

Neural networks are composed of neurons and synapses, which are responsible for learning in a slow adaptive dynamical process. Here we experimentally show that neurons act like independent anisotropic multiplex hubs, which relay and mute incoming signals following their input directions. Theoretically, the observed information routing enriches the computational capabilities of neurons by allowing, for instance, equalization among different information routes in the network, as well as high-frequency transmission of complex time-dependent signals constructed via several parallel routes. In addition, this kind of hubs adaptively eliminate very noisy neurons from the dynamics of the network, preventing masking of information transmission. The timescales for these features are several seconds at most, as opposed to the imprint of information by the synaptic plasticity, a process which exceeds minutes. Results open the horizon to the understanding of fast and adaptive learning realities in higher cognitive brain's functionalities.

Age-Related Differences in Reorganization of Functional Connectivity for a Dual Task with Increasing Postural Destabilization.

The aged brain may not make good use of central resources, so dual task performance may be degraded. From the brain connectome perspective, this study investigated dual task deficits of older adults that lead to task failure of a suprapostural motor task with increasing postural destabilization. Twelve younger (mean age: 25.3 years) and 12 older (mean age: 65.8 years) adults executed a designated force-matching task from a level-surface or a stabilometer board. Force-matching error, stance sway, and event-related potential (ERP) in the preparatory period were measured. The force-matching accuracy and the size of postural sway of the older adults tended to be more vulnerable to stance configuration than that of the young adults, although both groups consistently showed greater attentional investment on the postural task as sway regularity increased in the stabilometer condition. In terms of the synchronization likelihood (SL) of the ERP, both younger and older adults had net increases in the strengths of the functional connectivity in the whole brain and in the fronto-sensorimotor network in the stabilometer condition. Also, the SL in the fronto-sensorimotor network of the older adults was greater than that of the young adults for both stance conditions. However, unlike the young adults, the older adults did not exhibit concurrent deactivation of the functional connectivity of the left temporal-parietal-occipital network for postural-suprapostural task with increasing postural load. In addition, the older adults potentiated functional connectivity of the right prefrontal area to cope with concurrent force-matching with increasing postural load. In conclusion, despite a universal negative effect on brain volume conduction, our preliminary results showed that the older adults were still capable of increasing allocation of neural sources, particularly via compensatory recruitment of the right prefrontal loop, for concurrent force-matching under the challenging postural condition. Nevertheless, dual-task performance of the older adults tended to be more vulnerable to postural load than that of the younger adults, in relation to inferior neural economy or a slow adaptation process to stance destabilization for scant dissociation of control hubs in the temporal-parietal-occipital cortex.

Adaptation: A Two-Perception Probabilistic Conceptual Framework

We introduce a two-perception probabilistic concept of adaptation (TPPCA), which accounts for fast and slow adaptation processes. The outcome of both processes depends on the perceptual difference (termed herein a quantum) of how an individual perceives his or her abilities, skills, and capacities (βv) to interact, cope, and perform a given task (δi). Thus, the adaptation process is determined by (βv – δi). Fast adaptation processes target aspects that require immediate responses while slow adaptation processes involve ongoing adaptation to long-term demands. We introduce the TPPCA in several domains of inquiry, which rely on fast adaptation processes (perceptual–cognitive–action coupling, performance routines, psychological crisis, reversal states), slow adaptation processes (i.e., career aspirations, burnout), and processes that can be either fast or slow (i.e., flow, affect and mood changes, emotion regulation).

Are fast/slow process in motor adaptation and forward/inverse internal model two sides of the same coin?

Motor adaptation is tuning of motor commands to compensate the disturbances in the outside environment and/or in the sensory-motor system. In spite of various theoretical and empirical studies, mechanism by which the brain learns to adapt has not been clearly understood. Among different computational models, two lines of researches are of interest in this study: first, the models which assume two adaptive processes, i.e. fast and slow, for motor learning, and second, the computational frameworks which assume two types of internal models in the central nervous system (CNS), i.e., forward and inverse models. They explain motor learning by modifying these internal models. Here, we present a hypothesis for a possible relationship between these two viewpoints according to the computational and physiological findings. This hypothesis suggests a direct relationship between the forward (inverse) internal model and the fast (slow) adaptive process. That is, the forward (inverse) model and fast (slow) adaptive process can be two sides of the same coin. Further evaluation of this hypothesis is helpful to achieve a better understanding of motor adaptation mechanism in the brain and also it lends itself to be used in designing therapeutic programs for rehabilitation of certain movement disorders.

Kinetic adaptation during locomotion on a split-belt treadmill

It has been suggested that a feedforward control mechanism drives the adaptation of the spatial and temporal interlimb locomotion variables. However, the internal representation of limb kinetics during split-belt locomotion has not yet been studied. In hand movements, it has been suggested that kinetic and kinematic parameters are controlled by separate neural processes; therefore, it is possible that separate neural processes are responsible for kinetic and kinematic locomotion parameters. In the present study, we assessed the adaptation of the limb kinetics by analyzing the ground reaction forces (GRFs) as well as the center of pressure (COP) during adaptation to speed perturbation, using a split-belt treadmill with an integrated force plate. We found that both the GRF of each leg at initial contact and the COP changed gradually and showed motor aftereffects during early postadaptation, suggesting the use of a feedforward predictive mechanism. However, the GRF of each leg in the single-support period used a feedback control mechanism. It changed rapidly during the adaptation phase and showed no motor aftereffect when the speed perturbation was removed. Finally, we found that the motor adaptation of the GRF and the COP are mediated by a dual-rate process. Our results suggest two important contributions to neural control of locomotion. First, different control mechanisms are responsible for forces at single- and double-support periods, as previously reported for kinematic variables. Second, our results suggest that motor adaptation during split-belt locomotion is mediated by fast and slow adaptation processes.

Short term synaptic depression improves information transfer in perceptual multistability

Competitive neural networks are often used to model the dynamics of perceptual bistability. Switching between percepts can occur through fluctuations and/or a slow adaptive process. Here, we analyze switching statistics in competitive networks with short term synaptic depression and noise. We start by analyzing a ring model that yields spatially structured solutions and complement this with a study of a space-free network whose populations are coupled with mutual inhibition. Dominance times arising from depression driven switching can be approximated using a separation of timescales in the ring and space-free model. For purely noise-driven switching, we derive approximate energy functions to justify how dominance times are exponentially related to input strength. We also show that a combination of depression and noise generates realistic distributions of dominance times. Unimodal functions of dominance times are more easily told apart by sampling, so switches induced by synaptic depression induced provide more information about stimuli than noise-driven switching. Finally, we analyze a competitive network model of perceptual tristability, showing depression generates a history-dependence in dominance switching.

Oxygen and Oxidative Stress in the Neonatal Period

Aerobic metabolism in the mitochondria is highly efficient in providing energy for the living organisms. However, as byproducts, reactive oxygen species (ROS) are produced. Some of these chemical species are highly reactive-free radicals capable of causing functional and structural damage to cell components. To overcome free radical attack, cells have evolved both antioxidant defense and repairing systems. However, under certain circumstances the production of oxygen-free radicals overcomes antioxidant defense causing oxidative stress (OS) and damage. Newborn infants and especially preterm infants are endowed with an immature antioxidant defense and respiratory system and are therefore prone to OS. Too much oxygen may damage different organs (lung, brain, retina, and gastrointestinal tract), leading to severe acute and chronic conditions that will affect not only the survival but also the quality of life of these infants. Advances in our knowledge of oxygen metabolism, pathophysiology of oxygen-derived damage, and development of more efficient monitoring devices have drastically changed the scenario. We have learned that postnatal adaptation constitutes a slow adaptive process that needs more time than previously believed and that should be approached gently. Moreover, strict control of oxygen saturation as measured by pulse oximetry, while oxygen supplementation is needed, is also a relevant intervention contributing to reduce oxygen-derived deleterious consequences. Notwithstanding, the establishment of safe limits avoiding oxygen toxicity but not increasing the risk of mortality needs further studies. In this regard, the inclusion of new biomarkers may help clinicians to make better therapeutic decisions in the near future.

A Shared Resource between Declarative Memory and Motor Memory

The neural systems that support motor adaptation in humans are thought to be distinct from those that support the declarative system. Yet, during motor adaptation changes in motor commands are supported by a fast adaptive process that has important properties (rapid learning, fast decay) that are usually associated with the declarative system. The fast process can be contrasted to a slow adaptive process that also supports motor memory, but learns gradually and shows resistance to forgetting. Here we show that after people stop performing a motor task, the fast motor memory can be disrupted by a task that engages declarative memory, but the slow motor memory is immune from this interference. Furthermore, we find that the fast/declarative component plays a major role in the consolidation of the slow motor memory. Because of the competitive nature of declarative and nondeclarative memory during consolidation, impairment of the fast/declarative component leads to improvements in the slow/nondeclarative component. Therefore, the fast process that supports formation of motor memory is not only neurally distinct from the slow process, but it shares critical resources with the declarative memory system.

Prospective control abilities during visuo-manual tracking in children with 22q11.2 Deletion syndrome compared to age- and IQ-matched controls

To examine whether children with a 22q11.2 Deletion syndrome (22q11.2DS) are able to use prospective control, 21 children with 22q11.2DS (mean age = 9.6 ± 1.9; mean FSIQ = 73.05 ± 10.2) and 21 control children (mean age = 9.6 ± 1.9; mean FSIQ = 73.38 ± 12.0) were asked to perform a visuo-manual tracking task in which they had to track a cursor rhythmically between 2 target zones. Children with 22q11.2DS performed worse than the age- and IQ-matched controls (higher absolute time and distance errors) suggesting that the 22q11.2DS group experiences an additional (syndrome specific) processing deficit that cannot be attributed to their lower intellectual abilities. The 22q11.2DS group neither the control group improved their tracking performance throughout five identical full feedback conditions of the tracking task possibly due to a slow visuo-motor adaptation process, a short span of attention and cognitive flexibility impairments. The results showed that both the 22q11.2DS group and the controls had difficulties anticipating the movement of the target (prospective control) and thus are assumed to rely more on feedback instead of on an internal representation of the movement.

Dynamics of coupled adaptive elements: Bursting and intermittent oscillations generated by frustration in networks

Adaptation to environmental change is a common property of biological systems. Cells initially respond to external changes in the environment, but after some time, they regain their original state. By considering an element consisting of two variables that show such adaptation dynamics, we studied a coupled dynamical system containing such elements to examine the diverse dynamics in the system and classified the behaviors on the basis of the network structure that determined the interaction among elements. For a system with two elements, two types of behaviors, perfect adaptation and simple oscillation, were observed. For a system with three elements, in addition to these two types of dynamics, rapid-burst-type oscillation and a slow cycle were discovered; depending on the initial conditions, these two types of dynamics coexisted. These behaviors are a result of the characteristic dynamics of each element, i.e., fast response and slow adaptation processes. The behaviors depend on the network structure (in specific, a combination of positive or negative feedback among elements). Cooperativity among elements due to a positive feedback loop leads to simple oscillation, whereas frustration involving alternating positive and negative interactions among elements leads to the coexistence of rapid bursting oscillation and a slow cycle. These behaviors are classified on the basis of the frustration indices defined by the network structure. The period of the slow cycle is much longer than the original adaptation time scale, while the burst-type oscillation is a continued response that does not involve any adaptation. We briefly discuss the universal applicability of our results to a network of a larger number of elements and their possible relevance to biological systems.

ERG voltage‐gated K+ channels regulate excitability and discharge dynamics of the medial vestibular nucleus neurones

The discharge properties of the medial vestibular nucleus neurones (MVNn) critically depend on the activity of several ion channel types. In this study we show, immunohistochemically, that the voltage-gated K(+) channels ERG1A, ERG1B, ERG2 and ERG3 are highly expressed within the vestibular nuclei of P10 and P60 mice. The role played by these channels in the spike-generating mechanisms of the MVNn and in temporal information processing was investigated electrophysiologically from mouse brain slices, in vitro, by analysing the spontaneous discharge and the response to square-, ramp- and sinusoid-like intracellular DC current injections in extracellular and whole-cell patch-clamp studies. We show that more than half of the recorded MVNn were responsive to ERG channel block (WAY-123,398, E4031), displaying an increase in spontaneous activity and discharge irregularity. The response to step and ramp current injection was also modified by ERG block showing a reduction of first spike latency, enhancement of discharge rate and reduction of the slow spike-frequency adaptation process. ERG channels influence the interspike slope without affecting the spike shape. Moreover, in response to sinusoid-like current, ERG channel block caused frequency-dependent gain enhancement and phase-lead shift. Taken together, the data demonstrate that ERG channels control the excitability of MVNn, their discharge regularity and probably their resonance properties.

The Euro Changeover and Numerical Intuition for Prices in the Old and New Currencies

This study examines how numerical intuition for prices in euros and in the Portuguese currency escudos developed in Portugal after the euro changeover. Estimates of prices of 40 different products were collected in the two currencies and at four different times from November 2001 to April 2004. The results regarding price estimates in euros were more in accordance with a relearning hypothesis considering that price estimates become progressively more accurate by a process that is related to purchase frequency. It was also suggested that this is a very slow process and that prices in the former currency are not simply forgotten. On the contrary, the escudos remained a general benchmark for an extended period. The results regarding estimated price intuition and use of intuition in estimating prices are also consistent with a slow adaptation process. Implications for future euro changeovers are discussed.

PHR1, an integral membrane protein of the inner ear sensory cells, directly interacts with myosin 1c and myosin VIIa

By using the yeast two-hybrid technique, we identified a candidate protein ligand of the myosin 1c tail, PHR1, and found that this protein can also bind to the myosin VIIa tail. PHR1 is an integral membrane protein that contains a pleckstrin homology (PH) domain. Myosin 1c and myosin VIIa are two unconventional myosins present in the inner ear sensory cells. We showed that PHR1 immunoprecipitates with either myosin tail by using protein extracts from cotransfected HEK293 cells. In vitro binding assays confirmed that PHR1 directly interacts with these two myosins. In both cases the binding involves the PH domain. In vitro interactions between PHR1 and the myosin tails were not affected by the presence or absence of Ca2+ and calmodulin. Finally, we found that PHR1 is able to dimerise. As PHR1 is expressed in the vestibular and cochlear sensory cells, its direct interactions with the myosin 1c and VIIa tails are likely to play a role in anchoring the actin cytoskeleton to the plasma membrane of these cells. Moreover, as both myosins have been implicated in the mechanotransduction slow adaptation process that takes place in the hair bundles, we propose that PHR1 is also involved in this process.

Les relations gouvernement-monde des affaires dans la France de l'après-guerre : adaptations et adaptabilite d'un système original

Abstract The article gives an overview of the development of government-business relations in France from the end of the Second World War until today. It distinguishes three periods in terms of the degree and objectives of government intervention and the adaptation of the French system to a changing environment, including the role of European integration: (i) the immediate post-war years, characterised by industrial renewal and a gradual opening to international competition; (ii) the 1960s and 1970s with a focus on national champions and major infrastructure projects; and (iii) the 1980s and 1990s, when as results of the world-wide economic crises, budget constraints and Eu- ropean commitments, earlier mistakes became apparent and forced a major reorientation of industrial policy. The author argues that French business exercised a variable, but overall quite considerable influence on the decision-making process. Most policies were the result of bargaining, compromise and coalitions between different interest groups within the French administration and, more importantly, across the business-government divide. Quite often government action was a response to direct demands from influential industry and company representatives or, at least, an emanation of broader economic and societal trends. Even at times when government pressure was strongest, namely in the 1960s, business retained some influence. Adaptability was reduced though and only regained more recently following a slow and painful adaptation process.