Limb-related sensory prediction errors and task-related performance errors facilitate human sensorimotor learning through separate mechanisms.

The unpredictable nature of our world can introduce a variety of errors in our actions, including sensory prediction errors (SPEs) and task performance errors (TPEs). SPEs arise when our existing internal models of limb-environment properties and interactions become miscalibrated due to changes in the environment, while TPEs occur when environmental perturbations hinder achievement of task goals. The precise mechanisms employed by the sensorimotor system to learn from such limb- and task-related errors and improve future performance are not comprehensively understood.

A lateralized motor network in order to understand adaptation to visuomotor rotation.

The functional asymmetry between the two brain hemispheres in language and spatial processing is well documented. However, a description of difference in control between the two hemispheres in motor function is not well established. Our primary objective in this study was to examine the distribution of control in the motor hierarchy and its variation across hemispheres.

Spontaneous recovery in an untrained arm as an assay of interlimb transfer of motor learning.

Motor skills learned with one effector are known to transfer to an untrained effector. However, which of the many mechanisms that drive learning principally predict interlimb transfer, is less clear. Recent studies of motor adaptation suggest that transfer is tied to the state of an implicit mechanism that evolves gradually during learning.

Sensorimotor Learning in Response to Errors in Task Performance.

The human sensorimotor system is sensitive to both limb-related prediction errors and task-related performance errors. Prediction error signals are believed to drive implicit refinements to motor plans. However, an understanding of the mechanisms that performance errors stimulate has remained unclear largely because their effects have not been probed in isolation from prediction errors.

Symmetric interlimb transfer of newly acquired skilled movements.

In this study, we aimed to examine features of interlimb generalization or "transfer" of newly acquired motor skills, with a broader goal of better understanding the mechanisms mediating skill learning. Right-handed participants ( = 36) learned a motor task that required them to make very rapid but accurate reaches to one of eight randomly presented targets, thus bettering the typical speed-accuracy tradeoff. Subjects were divided into an "RL" group that first trained with the right arm and was then tested on the left and an "LR" group that trained with the left arm and was subsequently tested on the right.

Mechanistic determinants of effector-independent motor memory encoding.

Coordinated, purposeful movements learned with one effector generalize to another effector, a finding that has important implications for tool use, sports, performing arts, and rehabilitation. This occurs because the motor memory acquired through learning comprises representations that are effector-independent. Despite knowing this for decades, the neural mechanisms and substrates that are causally associated with the encoding of effector-independent motor memories remain poorly understood.

Laterality of Damage Influences the Relationship Between Impairment and Arm Use After Stroke.

Objectives: To investigate whether the relationship between arm use and motor impairment post-stroke is influenced by the hemisphere of damage.

Methods: Right-handed patients with unilateral left hemisphere damage (LHD) or right (RHD) (n=58; 28 LHD, 30 RHD) were recruited for this study. The Arm Motor Ability Test and Functional Impact Assessment were used to derive arm use patterns.

Interference between competing motor memories developed through learning with different limbs.

Learning from motor errors that occur across different limbs is essential for effective tool use, sports training, and rehabilitation. To probe the neural organization of error-driven learning across limbs, we asked whether learning opposing visuomotor mappings with the two arms would interfere. Young right-handers first adapted to opposite visuomotor rotations A and B with different arms and were then reexposed to A 24 h later.

The Neuropsychology of Movement and Movement Disorders: Neuroanatomical and Cognitive Considerations.

This paper highlights major developments over the past two to three decades in the neuropsychology of movement and its disorders. We focus on studies in healthy individuals and patients, which have identified cognitive contributions to movement control and animal work that has delineated the neural circuitry that makes these interactions possible. We cover advances in three major areas: (1) the neuroanatomical aspects of the "motor" system with an emphasis on multiple parallel circuits that include cortical, corticostriate, and corticocerebellar connections; (2) behavioral paradigms that have enabled an appreciation of the cognitive influences on the preparation and execution of movement; and (3) hemispheric differences (exemplified by limb praxis, motor sequencing, and motor learning).

Motor Adaptation Deficits in Ideomotor Apraxia.

Objectives: The cardinal motor deficits seen in ideomotor limb apraxia are thought to arise from damage to internal representations for actions developed through learning and experience. However, whether apraxic patients learn to develop new representations with training is not well understood. We studied the capacity of apraxic patients for motor adaptation, a process associated with the development of a new internal representation of the relationship between movements and their sensory effects.

Deep Breathing Practice Facilitates Retention of Newly Learned Motor Skills.

Paced deep breathing practices, a core component of a number of meditation programs, have been shown to enhance a variety of cognitive functions. However, their effects on complex processes such as memory, and in particular, formation and retention of motor memories, remain unknown. Here we show that a 30-minute session of deep, alternate-nostril breathing remarkably enhances retention of a newly learned motor skill.

Adaptive reliance on the most stable sensory predictions enhances perceptual feature extraction of moving stimuli.

The prediction of the sensory outcomes of action is thought to be useful for distinguishing self- vs. externally generated sensations, correcting movements when sensory feedback is delayed, and learning predictive models for motor behavior. Here, we show that aspects of another fundamental function-perception-are enhanced when they entail the contribution of predicted sensory outcomes and that this enhancement relies on the adaptive use of the most stable predictions available.

Error Detection is Critical for Visual-Motor Corrections.

The target article (Smeets, Oostwoud Wijdenes, & Brenner, 2016) proposes that short latency responses to changes in target location during reaching reflect an unconscious, continuous, and incremental minimization of the distance between the hand and the target, which does not require detection of the change in target location. We, instead, propose that short-latency visuomotor responses invoke reflex- or startle-like mechanisms, an idea supported by evidence that such responses are both automatic and resistant to cognitive influences. In addition, the target article fails to address the biological underpinnings for the range of response latencies reported across the literature, including the circuits that might underlie the proposed sensorimotor loops.

Learning of bimanual motor sequences in normal aging.

While it is well accepted that motor performance declines with age, the ability to learn simple procedural motor tasks appears to remain intact to some extent in normal aging. Here we examined the impact of aging on the acquisition of a simple sequence of bimanual actions. We further asked whether such learning results from an overall decrease in response time or is also associated with improved coordination between the hands.

The influence of visual target information on the online control of movements.

The continuously changing properties of our environment require constant monitoring of our actions and updating of our motor commands based on the task goals. Such updating relies upon our predictions about the sensory consequences of our movement commands, as well as sensory feedback received during movement execution. Here we focus on how visual information about target location is used to update and guide ongoing actions so that the task goal is successfully achieved.

Frontal and parietal cortex contributions to action modification.

Successful achievement of task goals depends critically on the ability to adjust ongoing actions in response to environmental changes. The neural substrates underlying action modification have been a topic of great controversy: both, posterior parietal cortex and frontal regions, particularly prefrontal cortex have been previously identified as crucial in this regard, with most studies arguing in favor of one or the other. We aimed to address this controversy and understand whether frontal and parietal regions might play distinct roles during action modification.

Rethinking motor lateralization: specialized but complementary mechanisms for motor control of each arm.

Motor lateralization in humans has primarily been characterized as "handedness", resulting in the view that one arm-hemisphere system is specialized for all aspects of movement while the other is simply a weaker analogue. We have proposed an alternative view that motor lateralization reflects proficiency of each arm for complementary functions that arises from a specialization of each hemisphere for distinct movement control mechanisms. However, before this idea of hemispheric specialization can be accepted, it is necessary to precisely identify these distinct, lateralized mechanisms.

Contralesional motor deficits after unilateral stroke reflect hemisphere-specific control mechanisms.

We have proposed a model of motor lateralization, in which the left and right hemispheres are specialized for different aspects of motor control: the left hemisphere for predicting and accounting for limb dynamics and the right hemisphere for stabilizing limb position through impedance control mechanisms. Our previous studies, demonstrating different motor deficits in the ipsilesional arm of stroke patients with left or right hemisphere damage, provided a critical test of our model. However, motor deficits after stroke are most prominent on the contralesional side.

The effects of brain lateralization on motor control and adaptation.

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.

Relationship between arm usage and instrumental activities of daily living after unilateral stroke.

Objective: To determine whether the preferred pattern of arm use after unilateral hemispheric damage was associated with better everyday functioning. Our previous work showed that right-handed stroke patients with right hemisphere damage (RHD) used their right, ipsilesional arm most frequently, while those with left hemisphere damage (LHD) used both arms together most frequently. This effect was explained by right-hand preference, but its relationship to functional performance is not known.

Critical neural substrates for correcting unexpected trajectory errors and learning from them.

Our proficiency at any skill is critically dependent on the ability to monitor our performance, correct errors and adapt subsequent movements so that errors are avoided in the future. In this study, we aimed to dissociate the neural substrates critical for correcting unexpected trajectory errors and learning to adapt future movements based on those errors. Twenty stroke patients with focal damage to frontal or parietal regions in the left or right brain hemispheres and 20 healthy controls performed a task in which a novel mapping between actual hand motion and its visual feedback was introduced.

Hemispheric specialization for movement control produces dissociable differences in online corrections after stroke.

In this study, we examine whether corrections made during an ongoing movement are differentially affected by left hemisphere damage (LHD) and right hemisphere damage (RHD). Our hypothesis of motor lateralization proposes that control mechanisms specialized to the right hemisphere rely largely on online processes, while the left hemisphere primarily utilizes predictive mechanisms to specify optimal coordination patterns. We therefore predict that RHD, but not LHD, should impair online correction when task goals are unexpectedly changed.

Left parietal regions are critical for adaptive visuomotor control.

The question addressed in this study is whether parietal brain circuits involved in adaptation to novel visuomotor conditions are lateralized. This information is critical for characterizing the neural mechanisms mediating adaptive behavior in humans, as well as for assessing the effects of unilateral brain damage on function. Moreover, previous research has been controversial in this regard.

Coordination deficits in ideomotor apraxia during visually targeted reaching reflect impaired visuomotor transformations.

Ideomotor limb apraxia, commonly defined as a disorder of skilled, purposeful movement, is characterized by spatiotemporal deficits during a variety of actions. These deficits have been attributed to damage to, or impaired retrieval of, stored representations of learned actions, especially object-related movements. However, such deficits might also arise from impaired visuomotor transformation mechanisms that operate in parallel to or downstream from mechanisms for storage of action representations.