The Effects of Brain Lateralization on Motor Control and Adaptation

ABSTRACT

Lateralization of mechanisms mediating functions such as language and perception is widely accepted as a fundamental feature of neural organization. Recent research has revealed that a similar organization exists for the control of motor actions, in that each brain hemisphere contributes unique control mechanisms to the movements of each arm. The authors review present research that addresses the nature of the control mechanisms that are lateralized to each hemisphere and how they impact motor adaptation and learning. In general, the studies suggest an enhanced role for the left hemisphere during adaptation, and the learning of new sequences and skills. The authors suggest that this specialization emerges from a left hemisphere specialization for predictive control—the ability to effectively plan and coordinate motor actions, possibly by optimizing certain cost functions. In contrast, right hemisphere circuits appear to be important for updating ongoing actions and stopping at a goal position, through modulation of sensorimotor stabilization mechanisms such as reflexes. The authors also propose that each brain hemisphere contributes its mechanism to the control of both arms. They also discuss the potential advantages of such a lateralized control system.     

Adaptation to a Nonlinear Visuomotor Amplitude Transformation With Continuous and Terminal Visual Feedback

The control of a cursor on a computer monitor offers a simple means of exploring the limits of the plasticity of human visuomotor coordination. The authors explored the boundary conditions for adaptation to nonlinear visuomotor amplitude transformations. The authors hypothesized that only with terminal visual feedback during practice, but not with continuous visual feedback, humans might develop an internal model of the nonlinear visuomotor amplitude transformation. Thus, 2 groups were engaged in a sensorimotor adaptation task receiving either continuous or terminal visual feedback during the practice phase. In contrast to expectations, adaptive shifts and aftereffects observed in visual open-loop tests were linearly related to target amplitudes for both groups. Although the 2 feedback groups did not differ with respect to adaptive shifts and aftereffects, terminal visual feedback resulted in stable visual open-loop performance for an extended period, whereas movement errors increased after continuous visual feedback during practice. The benefit of continuous visual feedback, on the other hand, was faster closed-loop performance, indicating an optimization of visual closed-loop control.     

Development of Force Adaptation During Childhood

Humans learn to make reaching movements in novel dynamic environments by acquiring an internal motor model of their limb dynamics. Here, the authors investigated how 4- to 11-year-old children (N = 39) and adults (N = 7) adapted to changes in arm dynamics, and they examined whether those data support the view that the human brain acquires inverse dynamics models (IDM) during development. While external damping forces were applied, the children learned to perform goal-directed forearm flexion movements. After changes in damping, all children showed kinematic aftereffects indicative of a neural controller that still attempted to compensate the no longer existing damping force. With increasing age, the number of trials toward complete adaptation decreased. When damping was present, forearm paths were most perturbed and most variable in the youngest children but were improved in the older children. The findings indicate that the neural representations of limb dynamics are less precise in children and less stable in time than those of adults. Such controller instability might be a primary cause of the high kinematic variability observed in many motor tasks during childhood. Finally, the young children were not able to update those models at the same rate as the older children, who, in turn, adapted more slowly than adults. In conclusion, the ability to adapt to unknown forces is a developmental achievement. The present results are consistent with the view that the acquisition and modification of internal models of the limb dynamics form the basis of that adaptive process.     

Neurocognitive Contributions to Motor Skill Learning: The Role of Working Memory

ABSTRACT

Researchers have begun to delineate the precise nature and neural correlates of the cognitive processes that contribute to motor skill learning. The authors review recent work from their laboratory designed to further understand the neurocognitive mechanisms of skill acquisition. The authors have demonstrated an important role for spatial working memory in 2 different types of motor skill learning, sensorimotor adaptation and motor sequence learning. They have shown that individual differences in spatial working memory capacity predict the rate of motor learning for sensorimotor adaptation and motor sequence learning, and have also reported neural overlap between a spatial working memory task and the early, but not late, stages of adaptation, particularly in the right dorsolateral prefrontal cortex and bilateral inferior parietal lobules. The authors propose that spatial working memory is relied on for processing motor error information to update motor control for subsequent actions. Further, they suggest that working memory is relied on during learning new action sequences for chunking individual action elements together.     

大学生人格特质、社会适应能力与网络成瘾倾向的关系

运用问卷调查法探讨了人格特质、社会适应能力和网络成瘾倾向的关系。对211位大学生(男120人,女91人)的调查结果表明:(1)精神质和社会适应能力对大学生网络成瘾倾向有直接影响;(2)精神质还通过社会适应能力间接影响网络成瘾倾向。     

Modulation of Gait During Visual Adaptation to Dark

The authors investigated the modulation of gait during dark adaptation. Twenty-five women (mean age = 72 years, SD = 5 years) walked back and forth on an arbitrarily uneven walkway during normal lighting at speeds ranging from slow to fast. Participants then performed 20 trials at preferred speed after sudden reduction of lighting; the authors compared those trials with point estimates at equivalent speeds representing normal lighting. The authors estimated speed, cadence, mediolateral trunk acceleration, and mediolateral interstep trunk-acceleration variability for each trial. Participants compensated for sudden reduction of lighting by reducing their walking speed. Compared with performance at equivalent speeds during normal lighting, cadence, trunk acceleration, and interstep trunk-acceleration variability initially increased. All variables showed an asymptotic approximation toward normal values during 60-90 s of walking in subdued lighting. The authors suggest that the sudden transition from normal to marginal lighting, rather than marginal lighting itself, may challenge locomotor control.     

First-Trial Adaptation to Prism Exposure

Terminal target-pointing error on the 1st trial of exposure to optical displacement is usually less than that expected from the optical displacement magnitude. Such 1st trial adaptation was confirmed in 2 experiments (N = 48 students in each) comparing pointing toward optically displaced targets and toward equivalent physically displaced targets (no optical displacement), with visual feedback delayed until movement completion. First-trial performance could not be explained by ordinary target undershoot, online correction, or reverse optic flow information about true target position and was unrelated to realignment aftereffects. Such adaptation might be an artifact of the asymmetry of the structured visual field produced by optical displacement, which induces a felt head rotation opposite to the direction of the displacement, thereby reducing the effective optical displacement.     

Calibration and Alignment are Separable: Evidence From Prism Adaptation

In 2 prism adaptation experiments, the authors investigated the effects of limb starting position visibility (visible or not visible) and visual feedback availability (early or late in target pointing movements). Thirty-two students participated in Experiment 1 and 24 students participated in Experiment 2. Independent of visual feedback availability, constant error was larger and variable error was smaller for target pointing when limb starting position was visible during prism exposure. Independent of limb starting position visibility, aftereffects of prism exposure were determined by visual feedback availability. Those results support the hypothesis that calibration is determined by limb starting position visibility, whereas alignment is determined separately by visual feedback availability.     

Strategie Calibration and Spatial Alignment: A Model From Prism Adaptation

Two types of adaptive processes involved in prism adaptation have been identified: slower spatial realignment among the several unique sensorimotor coordinate systems (spatial maps) and faster strategic motor control responses (including skill learning and calibration) to spatial misalignment. One measures the 1st process by assessing the aftereffects of prism exposure, whereas direct effects of the prism during exposure are a measure of the 2nd process. A model is described that relates those adaptive processes and distinguishes between extraordinary alignment and ordinary calibration. A conformal translation algorithm that operates on the hypothesized circuitry is proposed. The authors apply the model to explain the advantage of visual calibration when the limb is seen in the starting position prior to movement initiation. Implications of the model for the use of prism adaptation as a tool for investigation of motor control and learning are discussed.     

Adaptation in Visuomanual Tracking Depends on Intact Proprioception

The role of arm proprioception in motor learning was investigated in experiments in which, by moving the arm, subjects followed the motion of a target displayed on a monitor screen. Adaptive capabilities were tested in visuomanual tracking tasks following alterations in the relationship between the observer's actual arm movement and visual feedback of the arm movement given by a cursor motion on the screen. Tracking performance and adaptive changes, measured in terms of spatiotemporal error, tracking trajectory curvature, and spatial gain, were compared in 7 control subjects (CSs) and in 1 deafferented subject (DS). CSs adapted appropriately to altered visuomanual relationships; those changes were present in trials immediately after restoration of normal scaling. In contrast, although the DS modified his tracking strategy from trial to trial according to the altered conditions, he did not show plastic changes in internal visuomanual scaling. Like the results of prismatic adaptation experiments, the present results suggest that arm proprioception contributes to the plastic changes that follow alterations in the scaling of visuomanual gain.     

Frames of Reference for Human Perceptual-Motor Coordination: Space-Based Versus Joint-Based Adaptation

In this study, the authors addressed the issue of whether space-based motor planning occurs at a higher, equal, or lower level of central nervous system control than joint-based motor planning by using a computerized adaptation paradigm. Visual displays of participants' (N = 32) reaching movements to spatial targets were distorted either with respect to spatial hand displacements (space-based distortion) or with respect to joint angle displacements (joint-based distortion). Participants adapted more easily to space-based distortion than to joint-based distortion. The results suggest that when the participants were confronted with new visuomotor mappings, they aimed for virtual spatial targets whose positions were adjusted to compensate for the distortions associated with the new mappings. That strategy was preferred over a joint- or posture-based strategy, in which a posture is selected for the displayed spatial target and is then modified so that the new mapping between adopted and seen positions can be accommodated. The results support the widely held view that space-based planning occurs at a higher level than joint-based planning.     

Effect of Concurrent Visual Feedback Frequency on Postural Control Learning in Adolescents

The purpose was to find better augmented visual feedback frequency (100% or 67%) for learning a balance task in adolescents. Thirty subjects were divided randomly into a control group, and 100% and 67% feedback groups. The three groups performed pretest (3 trials), practice (12 trials), posttest (3 trials) and retention (3 trials, 24 hours later). The reduced feedback group showed lower RMS in the posttest than in the pretest (p = 0.04). The control and reduced feedback groups showed significant lower median frequency in the posttest than in the pretest (p < 0.05). Both feedback groups showed lower values in retention than in the pretest (p < 0.05). Even when the effect of feedback frequency could not be detected in motor learning, 67% of the feedback was recommended for motor adaptation.     

Discordance in Recovery Between Altered Locomotion and Muscle Atrophy Induced by Simulated Microgravity in Rats

Exposure to a microgravity environment leads to adverse effects in motion and musculoskeletal properties. However, few studies have investigated the recovery of altered locomotion and muscle atrophy simultaneously. The authors investigated altered locomotion in rats submitted to simulated microgravity by hindlimb unloading for 2 weeks. Motion deficits were characterized by hyperextension of the knees and ankle joints and forward-shifted limb motion. Furthermore, these locomotor deficits did not revert to their original form after a 2-week recovery period, although muscle atrophy in the hindlimbs had recovered, implying discordance in recovery between altered locomotion and muscle atrophy, and that other factors such as neural drives might control behavioral adaptations to microgravity.     

Stress and Adaptation

ABSTRACT— Animal models have contributed considerably to the current understanding of mechanisms underlying the role of stress in health and disease. Despite the progress made already, much more can be made by more carefully exploiting animals' and humans' shared biology, using ecologically relevant models. This allows a fundamental analysis of factors modulating individual adaptive capacity and hence individual vulnerability to disease. This article highlights an emerging scientific approach that uses a framework of interpretation that is more biologically oriented than previous approaches, to evaluate both the adaptive and maladaptive nature of the stress response in relation to existing environmental demands.     

Effects of Pointing Rate and Availability of Visual Feedback on Visual and Proprioceptive Components of Prism Adaptation

The withdrawal of vision of the arm during a manual aiming task has been found to result in a large increase in aiming error, regardless of the amount of practice in normal vision before its withdrawal. In the present study, the authors investigated whether the increase in error reflects the domination of visual afferent information over the movement representation developed during practice to the detriment of other sources of afferent information or whether it reflects only transformation errors of the location of the target from an allocentric to an egocentric frame of reference. Participants (N = 40) performed aiming movements with their dominant or nondominant arm in a full-vision or target-only condition. The results of the present experiment supported both of those hypotheses. The data indicated that practice does not eliminate the need for visual information for optimizing movement accuracy and that learning is specific to the source or sources of afferent information more likely to ensure optimal accuracy during practice. In addition, the results indicated that movement planning in an allocentric frame of reference might require simultaneous vision of the arm and the target. Finally, practice in a target-only condition, with knowledge of results, was found to improve recoding of the target in an egocentric frame of reference.     

Discrete Visual Samples May Control Locomotor Equilibrium and Foot Positioning in Man

The static or dynamic visual cues required for equilibrium as well as for foot guidance in visually guided locomotion in man were studied using a variety of locomotion supports and illumination and visual conditions. Stroboscopic illumination (brief flashes) and intermittent lighting (longer flashes) were used to control and to vary the visual sampling frequency of static (positional/orientational) visual cues. There were three main findings: First, visual control of foot positioning during locomotion over discontinuous terrain depends mainly upon static visual cues with a low sampling frequency (about 3 Hz); second, visual control of dynamic equilibrium during locomotion over a narrow support depends mainly upon the availability of high frequency static visual cues (up to about 12 Hz); and third, static visual cues required for equilibrium control are extracted from both the peripheral and the central visual field.

Assuming that discrete demands for feedback occur, a simple probabilistic model was proposed, according to which the mean time that elapses following presentation of static visual cues about positions or changes of position accounts for the differences in the difficulty of the various illumination conditions.     

Cognitive Load and Prism Adaptation

Subjects wore goggles with prisms that laterally displaced the visual field (rightward by 11.4°) and with full view of the limb engaged in paced (2-s rate) sagittal pointing at either an implicit (“straight ahead of the nose”) target (Experiment 1) or an explicit (positioned leftward by 11.4°) target (in Experiment 2). In experimental conditions, subjects performed a secondary cognitive task (mental arithmetic) simultaneously during target pointing. In control conditions, no cognitive load was imposed. Aftereffect measures of adaptation to the prismatic displacement were not substantially different when problem solving was required, but terminal error of the exposure pointing task was reliably affected by cognitive load. These results are consistent with the hypothesis of separable mechanisms for adaptive coordination and adaptive alignment. Adaptive coordination may be mediated by strategically flexible coordinative linkage between sensory–motor systems (eye–head and hand—head), but spatial alignment seems to be mediated by adaptive encoders within coordinatively linked subsystems. If the coordination task involves predominately automatic processing, coordinative linkage can be frequent enough under cognitive load for substantial realignment to occur even though exposure performance (adaptive coordination) may be less than optimal.     

分散注意条件下学优生与学困生视空间工作记忆的比较研究

通过控制干扰刺激量 ,研究分散注意对学优生和学困生视空间WM的影响。实验一的结果表明 :在不同干扰条件下 ,学困生视空间WM均比学优生差 ;干扰任务不仅影响学困生视空间WM的加工能力 ,也影响他们的存储能力。这说明学困生不能有效抑制外界干扰可能是他们视空间WM存在缺陷的主要原因之一。实验二的结果表明 :视空间WM有缺陷是各类学困生普遍存在的问题 ;对于学优生来说 ,不同类型学优生视空间WM不同 ,语文学优比数学学优的学生的视空间WM能力更强 ,主要表现在加工功能上。     

The Effects of Initial Habit Strength Differences Upon Performance in a Coaction Situation

The present investigation examined the effects of initial habit strength differences upon performance in a coaction situation. During a training session, a habit-strength hierarchy was developed in each of three groups through the establishment of a differential response expectancy for each of four alternative responses. In a subsequent test session, both performance and consistency of performance were affected by the pretraining on the correct habit. However, there was no statistical support for the hypothesis that coaction would interact with the habit-strength condition resulting in an improvement in the coaction/habit-correct group and a decrement in the coaction/habit-incorrect group. Similarly, no differences were found between the coaction and alone conditions.