Learning from Sensory and Reward Prediction Errors during Motor Adaptation

Voluntary motor commands produce two kinds of consequences. Initially, a sensory consequence is observed in terms of activity in our primary sensory organs (e.g., vision, proprioception). Subsequently, the brain evaluates the sensory feedback and produces a subjective measure of utility or usefulness of the motor commands (e.g., reward). As a result, comparisons between predicted and observed consequences of motor commands produce two forms of prediction error. How do these errors contribute to changes in motor commands? Here, we considered a reach adaptation protocol and found that when high quality sensory feedback was available, adaptation of motor commands was driven almost exclusively by sensory prediction errors. This form of learning had a distinct signature: as motor commands adapted, the subjects altered their predictions regarding sensory consequences of motor commands, and generalized this learning broadly to neighboring motor commands. In contrast, as the quality of the sensory feedback degraded, adaptation of motor commands became more dependent on reward prediction errors. Reward prediction errors produced comparable changes in the motor commands, but produced no change in the predicted sensory consequences of motor commands, and generalized only locally. Because we found that there was a within subject correlation between generalization patterns and sensory remapping, it is plausible that during adaptation an individual's relative reliance on sensory vs. reward prediction errors could be inferred. We suggest that while motor commands change because of sensory and reward prediction errors, only sensory prediction errors produce a change in the neural system that predicts sensory consequences of motor commands

Geometric Structure of the Adaptive Controller of the Human Arm

The objects with which the hand interacts with may significantly change the dynamics of the arm. How does the brain adapt control of arm movements to this new dynamic? We show that adaptation is via composition of a model of the task's dynamics. By exploring generalization capabilities of this adaptation we infer some of the properties of the computational elements with which the brain formed this model: the elements have broad receptive fields and encode the learned dynamics as a map structured in an intrinsic coordinate system closely related to the geometry of the skeletomusculature. The low--level nature of these elements suggests that they may represent asset of primitives with which a movement is represented in the CNS

Clinical Management of Dens Invaginatus Type 3: A Case Report

ABSTRACT: Dens invagination (DI) is a developmental abnormality of teeth which frequently results in a complex internal anatomy of the root canal system. DI type 3 is an anomaly characterized by infolding of enamel and dentin extending into the root apex. This may present difficulties when forming a diagnosis and treatment plan. Many treatment modalities have been presented in case reports for DI type 3, but there is insufficient evidence to recommend a therapy. This case report presents the successful non surgical root canal treatment of a maxillary canine with an open apex DI type 3, necrotic pulp, and an associated large periradicular lesion

Error Correction, Sensory Prediction, and Adaptation in Motor Control

Motor control is the study of how organisms make accurate goal-directed movements. There are two problems that the motor system must solve in order to achieve such control. The first problem is that sensory feedback is noisy and delayed, which can make movements inaccurate and unstable. The second problem is that the relationship between a motor command and the movement it produces is variable, as the body and the environment can both change. A solution is to build adaptive internal models of the body and the world. The predictions of these internal models, called forward models because they transform motor commands into sensory consequences, can be used to both produce a lifetime of calibrated movements, and to improve the ability of the sensory system to estimate the state of the body and the world around it. Forward models are only useful if they produce unbiased predictions. Evidence shows that forward models remain calibrated through motor adaptation: learning driven by sensory prediction errors.Engineering and Applied Science

Interacting Adaptive Processes with Different Timescales Underlie Short-Term Motor Learning

Multiple processes may contribute to motor skill acquisition, but it is thought that many of these processes require sleep or the passage of long periods of time ranging from several hours to many days or weeks. Here we demonstrate that within a timescale of minutes, two distinct fast-acting processes drive motor adaptation. One process responds weakly to error but retains information well, whereas the other responds strongly but has poor retention. This two-state learning system makes the surprising prediction of spontaneous recovery (or adaptation rebound) if error feedback is clamped at zero following an adaptation-extinction training episode. We used a novel paradigm to experimentally confirm this prediction in human motor learning of reaching, and we show that the interaction between the learning processes in this simple two-state system provides a unifying explanation for several different, apparently unrelated, phenomena in motor adaptation including savings, anterograde interference, spontaneous recovery, and rapid unlearning. Our results suggest that motor adaptation depends on at least two distinct neural systems that have different sensitivity to error and retain information at different rates

Effect of Nonsurgical Periodontal Treatment Combined With Diode Laser or Photodynamic Therapy on Chronic Periodontitis: A Randomized Controlled Split-Mouth Clinical Trial

Introduction: The optimum removal of bacteria and their toxins from periodontal pockets is not always obtained by conventional mechanical debridement. Adjunctive therapies may improve tissue healing through detoxification and bactericidal effects. The purpose of the present study was to evaluate the impact of adjunctive laser therapy (LT) and photodynamic therapy (PDT) on patients with chronic periodontitis.Methods: Twenty patients with at least three quadrants involved and each of them presenting pockets 4-8 mm deep were included in the study. Periodontal treatment comprising scaling and root planning (SRP) was accomplished for the whole mouth. Applying a split-mouth design, each quadrant was randomly treated with SRP alone (group A), SRP with LT (group B), and SRP with PDT (group C). The clinical indices were measured at baseline 6 weeks and 3 months after treatment. Microbiological samples were taken and evaluated at baseline and 3-month follow-up. Results: All groups showed statistically significant improvements in terms of clinical attachment level (CAL) gain, periodontal pocket depth (PPD) reduction, papilla bleeding index and microbial count compared to baseline (P < .05). The results showed more significant improvement in the 6-week evaluation in terms of CAL in groups B and C than in group A (P < .05). Group B also revealed a greater reduction in PPD than the other treatment modalities (P < .05).Conclusion: The obtained data suggested that adjunctive LT and PDT have significant short-term benefits in the treatment of chronic periodontitis. Furthermore, LT showed minimal additional advantages compared to PDT

A Gain-Field Encoding of Limb Position and Velocity in the Internal Model of Arm Dynamics

Adaptability of reaching movements depends on a computation in the brain that transforms sensory cues, such as those that indicate the position and velocity of the arm, into motor commands. Theoretical consideration shows that the encoding properties of neural elements implementing this transformation dictate how errors should generalize from one limb position and velocity to another. To estimate how sensory cues are encoded by these neural elements, we designed experiments that quantified spatial generalization in environments where forces depended on both position and velocity of the limb. The patterns of error generalization suggest that the neural elements that compute the transformation encode limb position and velocity in intrinsic coordinates via a gain-field; i.e., the elements have directionally dependent tuning that is modulated monotonically with limb position. The gain-field encoding makes the counterintuitive prediction of hypergeneralization: there should be growing extrapolation beyond the trained workspace. Furthermore, nonmonotonic force patterns should be more difficult to learn than monotonic ones. We confirmed these predictions experimentally

Effects of Human Cerebellar Thalamus Disruption on Adaptive Control of Reaching

Lesion or degeneration of the cerebellum can profoundly impair adaptive control of reaching in humans. Computational models have proposed that internal models that help control movements form in the cerebellum and influence planned motor output through the cerebello-thalamo-cortical pathway. However, lesion studies of the cerebellar thalamus have not consistently found impairment in reaching or adaptation of reaching. To elucidate the role of the cerebellar thalamus in humans, we studied a group of essential tremor (ET) patients with deep brain stimulation (DBS) electrodes placed in the cerebellar thalamus. The stimulation can be turned on or off remotely and is thought to reduce tremor by blocking the spread of the pathological output from the cerebellum. We studied the effect of thalamic DBS on the ability to adapt arm movements to novel force fields. Although thalamic DBS resulted in a dramatic and significant reduction of tremor in ET, it also impaired motor adaptation: the larger the stimulation voltage, the greater the reduction in rates of adaptation. We next examined ET patients that had undergone unilateral thalamotomy in the cerebellar thalamus and found that adaptation with the contralateral arm was impaired compared with the ipsilateral arm. Therefore, although both lesion and electrical stimulation of the cerebellar thalamus are highly effective in reducing tremor, they significantly impair the ability of the brain to form internal models of action. Adaptive control of reaching appears to depend on the integrity of the cerebello-thalamo-cortical pathway.Engineering and Applied Science

Generalization of Motor Learning Depends on the History of Prior Action

Generalization of motor learning refers to our ability to apply what has been learned in one context to other contexts. When generalization is beneficial, it is termed transfer, and when it is detrimental, it is termed interference. Insight into the mechanism of generalization may be acquired from understanding why training transfers in some contexts but not others. However, identifying relevant contextual cues has proven surprisingly difficult, perhaps because the search has mainly been for cues that are explicit. We hypothesized instead that a relevant contextual cue is an implicit memory of action with a particular body part. To test this hypothesis we considered a task in which participants learned to control motion of a cursor under visuomotor rotation in two contexts: by moving their hand through motion of their shoulder and elbow, or through motion of their wrist. Use of these contextual cues led to three observations: First, in naive participants, learning in the wrist context was much faster than in the arm context. Second, generalization was asymmetric so that arm training benefited subsequent wrist training, but not vice versa. Third, in people who had prior wrist training, generalization from the arm to the wrist was blocked. That is, prior wrist training appeared to prevent both the interference and transfer that subsequent arm training should have caused. To explain the data, we posited that the learner collected statistics of contextual history: all upper arm movements also move the hand, but occasionally we move our hands without moving the upper arm. In a Bayesian framework, history of limb segment use strongly affects parameter uncertainty, which is a measure of the covariance of the contextual cues. This simple Bayesian prior dictated a generalization pattern that largely reproduced all three findings. For motor learning, generalization depends on context, which is determined by the statistics of how we have previously used the various parts of our limbs

Correlation between the muscle, blood and heart level of Irisin in exercise-trained rats with Nano selenium supplementation: A rat model of COPD

The aim of this study was to considering the correlation between the muscle fibronectin type III domain-containing protein 5 (FNDC5), blood and heart level of Irisin in exercise-trained rats with Nano selenium supplementation after intraperitoneal injection of cigarette smoke extract induced chronic obstructive pulmonary disease (COPD). To this end, 49 male Wistar rats (8 weeks old) were divided into seven groups: control, SeNPs (2.5 mg/kg b.w by oral gavage, 3 days/week, 6 weeks), AIT (49 min/day, 5 days/week for 6 weeks, interval), SeNPs+AIT, CSE (150 µL by IP injection, 1 day/week for 6 weeks), CSE+AIT, and CSE+SeNPs+AIT. The results of the present study showed that CSE injection caused inflammation and damage to lung tissue, especially alveoli, compared to the healthy group. In other words, based on the histological examination of cigarette smoke extract, it was able to cause lung tissue damage similar to COPD, and doing exercise and taking nanoselenium antioxidant supplement could control these lung tissue damage. Pearson's correlation method was used to investigate the relationship between muscle FNDC5, serum and heart Irisin, and the results of this correlation were not significant in different groups (p>0.05). It seems that exercising and taking nanoselenium supplements can increase Irisin levels in serum and heart tissue by expanding muscle contraction and increasing muscle FNDC5. However, the relationship of this factor in muscle and heart crosstalk should be investigated more closely