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Two experiments required right-handed subjects to trace circular trajectories while complying with either a symmetric or asymmetric pattern. In symmetric patterns, circles were traced in a mirror image either inward or outward. In asymmetric patterns, circles were traced in the same direction either clockwise or counterclockwise. Subjects were instructed to trace with spatial accuracy while maintaining a strict temporal relationship to a metronome that scaled movement rates from 1.25 to 3 Hz. The symmetric patterns were more stable than asymmetric patterns; the circularity of trajectories was greater for the dominant side; and there were spontaneous reversals in the direction of circling in the nondominant limb when performing asymmetric patterns. The second experiment examined the same subjects under the instruction of intentionally changing the pattern by reversing the left or right limb circling direction when cued to do so. The degree of interlimb interference was highly asymmetric and contingent on the direction of pattern change. Intentional direction reversals were more expedient and with less disruption to the contralateral limb when asymmetric to symmetric pattern changes were effected through a reversal in the direction of nondominant side. The results are interpreted with reference to evidence that the supplementary motor area mediates descending input to the upper limbs during disparate bimanual actions, but not during symmetric actions. [ABSTRACT FROM AUTHOR]

Seven right-handed participants performed bimanual circling movements in either a symmetrical or an asymmetrical coordination mode. Movements were paced with an auditory metronome at predetermined frequencies corresponding to transition frequency, where asymmetrical patterns became unstable, or at two-thirds transition frequency where both symmetrical and asymmetrical patterns were stable. The pacing tones were presented in either a high (1000 Hz) or low (500 Hz) pitch, and the percentage of high-pitched tones during a 20 s trial varied between 0% and 70%. Participants were instructed to count the number of high-pitched pacing tones that occurred during a trial of bimanual circling. Overall, the symmetrical pattern was more stable than the asymmetrical pattern at both frequencies. Errors on the tone-counting task were significantly higher during asymmetrical circling than symmetrical circling but only at the transition movement frequency. The results suggest that cognitive processes play a role in maintaining coordination patterns within regions of instability. [ABSTRACT FROM AUTHOR]

Competing Interests: Declarations of interest None of the authors have potential conflicts of interest to be disclosed.

The stop-signal paradigm has become ubiquitous in investigations of inhibitory control. Tasks inspired by the paradigm, referred to as stop-signal tasks, require participants to make responses on go trials and to inhibit those responses when presented with a stop-signal on stop trials. Currently, the most popular version of the stop-signal task is the 'choice-reaction' variant, where participants make choice responses, but must inhibit those responses when presented with a stop-signal. An alternative to the choice-reaction variant of the stop-signal task is the 'anticipated response inhibition' task. In anticipated response inhibition tasks, participants are required to make a planned response that coincides with a predictably timed event (such as lifting a finger from a computer key to stop a filling bar at a predefined target). Anticipated response inhibition tasks have some advantages over the more traditional choice-reaction stop-signal tasks and are becoming increasingly popular. However, currently, there are no openly available versions of the anticipated response inhibition task, limiting potential uptake. Here, we present an open-source, free, and ready-to-use version of the anticipated response inhibition task, which we refer to as the OSARI (the Open-Source Anticipated Response Inhibition) task., (© 2021. Crown.)

Being able to predict an individual's potential for recovery of motor function after stroke may facilitate the use of more effective targeted rehabilitation strategies, and management of patient expectations and goals. This review summarises developments since 2010 of approaches based on clinical, neurophysiological and neuroimaging measures for predicting individual patients' potential for upper limb recovery. Clinical assessments alone have low prognostic accuracy. Transcranial magnetic stimulation can be used to assess the functional integrity of the corticomotor pathway, and has some predictive value but is not superior when used in isolation due to its low negative predictive value. Neuroimaging measures can be used to assess the structural integrity of descending white matter tracts. Recent studies indicate that the integrity of corticospinal and alternate motor tracts in both hemispheres may be useful predictors of motor recovery after stroke. The PREP algorithm is currently the only sequential algorithm that combines clinical, neurophysiological and neuroimaging measures at the sub-acute stage to predict the potential for subsequent recovery of upper limb function. Future research could determine if a similar algorithmic approach may be useful for predicting the recovery of gait after stroke., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)

Constraints pertaining to interlimb coordination have been studied extensively in the past decades. In this debate, F. Mechsner (2004) has taken a provocative position by putting primary emphasis on perceptual principles that mediate coordinative stability. Whereas the present authors agree that the role of perceptual principles is of critical importance during coordination, they take issue with Mechsner's extreme position and with the evidence forwarded to support a purely perceptual-cognitive approach to bimanual coordination. More specifically, the authors emphasize that current knowledge about brain function argues against a dualism between perception and action, criticize the presented evidence that posture manipulations during coordination provide decisive evidence against motoric and muscular constraints, and report on potential pitfalls associated with the use of visual transformation procedures to support complex coordination patterns.

A procedure is outlined in which the excitability of the corticomotor pathway is examined during rhythmic, passive upper limb movement. Using a custom built apparatus and software, wrist flexion-extension movements of a programmable frequency, amplitude and duration are induced while transcranial magnetic stimuli are delivered to the contralateral cortex over the area representing the flexor carpi radialis muscle. Stimuli are timed to occur during different phases of the movement cycle in order to examine the influence of ascending sensory input on the excitability of the corticospinal pathway. The protocol enables modulations in evoked responses to be analysed during movement of different frequencies and amplitudes, and permits alterations in cortical excitability to be examined by using paired pulse paradigms. The technique may also be utilised to examine hemispheric and segmental transfer if a stationary target limb is probed while the contralateral limb is passively moved. The protocol has potential use in examining corticomotor excitability in subjects with deficits in sensory and/or motor function, such as patients with Parkinson's disease or individuals recovering from stroke.

Using transcranial magnetic stimulation (TMS) over the contralateral motor cortex, motor evoked potentials (MEPs) were recorded from resting abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles of eight subjects while they either rested or produced one of six levels of force with the APB ipsilateral to the TMS. F-waves were recorded from each APB at rest in response to median nerve stimulation while subjects either rested or produced one of two levels of force with their contralateral APB. Contraction of the APB ipsilateral to TMS produced facilitation of the MEPs recorded from resting APB and FDI muscles contralateral to TMS but did not modulate F-wave amplitude. Negligible asymmetries in MEP facilitation were observed between dominant and subdominant hands. These results suggest that facilitation arising from isometric contraction of ipsilateral hand muscles occurs primarily at supraspinal levels, and this occurs symmetrically between dominant and subdominant hemispheres.

Upper limb coordination was studied by examining pattern stability of between-hand rhythmical coordination. In the first of two experiments, relative phase of rhythmical wrist flexion-extension was examined within a kinesthetic tracking paradigm. Eight right-handed subjects actively tracked a driven hand being flexed and extended by a computer-controlled AC servo-motor. Hand movements were constrained in flexion or extension. The simultaneous contraction of wrist flexors and extensors was defined as inphase (IP) and the alternating contraction of wrist flexors and extensors as antiphase (AP). Phase transitions (from AP to IP) were observed in 16% of trials prepared in AP. Fewer phase transitions occurred when the right wrist was constrained in flexion, and also when the left wrist was constrained in extension. IP patterns were performed with greater stability than AP patterns. These effects were explored further in a second experiment with the addition of a secondary probe reaction time task to assess demands on central capacity, and the analysis of wrist flexor and extensor electromyographic activity. Subjects returned longer reaction times for AP than IP movement, suggesting the AP movement pattern placed a greater demand on central capacity than the IP movement pattern. During this kinesthetic tracking task, similar dynamic principles emerged as those observed during bilaterally active bimanual rhythmical coordination. The greater stability of the hand-posture combination where the driven left hand was constrained in extension and the active right hand was constrained in flexion may be a demonstration of unique central control of coupled activity.

Subjects performed a bimanual circle-tracing task in time with an auditory metronome while restricted to moving with either proximal or distal musculature of the upper limb. Patterns were made in symmetric or asymmetric directions with respect to the midline. Symmetric patterns were more stable than asymmetric patterns. In response to a visual stimulus, subjects reversed the direction of one limb. Unwanted disruptions (momentary or lasting reversals) in the limb contralateral to the reversing limb were observed in 48% of trials. Incidence of disruption was equivalent between postures, but occurred more frequently when the dominant hand reversed direction. This result is consistent with anisotropy in coupling between hands and reveals a unifying constraint between spontaneous and intentional dynamics in bimanual coordination.

In the first of three experiments, 11 participants generated pronation and supination movements of the forearm. in time with an auditory metronome. The metronome frequency was increased in eight steps (0.25 Hz) from a base frequency of 1.75 Hz. On alternating trials, participants were required to coordinate either maximum pronation or maximum supination with each beat of the metronome. In each block of trials, the axis of rotation was either coincident with the long axis of the forearm, above this axis, or below this axis. The stability of the pronate-on-the-beat pattern, as indexed by the number of pattern changes, and the time of onset of pattern change, was greatest when the axis of rotation of the movement was below the long axis of the forearm. In contrast, the stability of the supinate-on-the-beat pattern was greatest when the axis of rotation of the movement was above the long axis of the forearm. In a second experiment, we examined how changes in the position of the axis of rotation alter the activation patterns of muscles that contribute to pronation and supination of the forearm. Variations in the relative dominance of the pronation and supination phases of the movement cycle across conditions were accounted for primarily by changes in the activation profile of flexor carpi radialis (FCR) and extensor carpi radialis longus (ECR). In the final experiment we examined how these constraints impact upon the stability of bimanual coordination. Thirty-two participants were assigned at random to one of four conditions, each of which combined an axis of rotation configuration (bottom or top) for each limb. The participants generated both inphase (both limbs pronating simultaneously, and supinating simultaneously) and antiphase (left limb pronating and right limb supinating simultaneously, and vice versa) patterns of coordination. When the position of the axis of rotation was equivalent for the left and the right limb, transitions from antiphase to inphase patterns of coordination were frequently observed. In marked contrast, when the position of the axis of rotation for the left and right limb was contradistinct, transitions from inphase to antiphase patterns of coordination occurred. The results demonstrated that when movements are performed in an appropriate mechanical context, inphase patterns of coordination are less stable than antiphase patterns.

Two simple experiments reveal that the ease with which an action is performed by the neuromuscular-skeletal system determines the attentional resources devoted to the movement. Participants were required to perform a primary task, consisting of rhythmic flexion and extension movements of the index finger, while being paced by an auditory metronome, in one of two modes of coordination: flex on the beat or extend on the beat. Using a classical dual-task methodology, we demonstrated that the time taken to react to an unpredictable visual probe stimulus (the secondary task) by means of a pedal response was greater when the extension phase of the finger movement sequence was made on the beat of the metronome than when the flexion phase was coordinated with the beat. In a second experiment, the posture of the wrist was manipulated in order to alter the operating lengths of muscles that flex and extend the index finger. The attentional demands of maintaining the extend-on-the-beat pattern of coordination were altered in a systematic fashion by changes in wrist posture, even though the effector used to respond to the visual probe stimulus was unaffected.

Three experiments are reported in which subjects made rapid aiming movements to visual targets with their left and right hands. In Experiments 1 and 3, a precue protocol was employed. In the "simple" reaction time condition, subjects were precued with complete information concerning the target position. In the four-choice condition, subjects were precued with partial information, indicating a subset of four possible target positions. In the eight-choice condition, advance information regarding the target position was entirely ambiguous. Results indicated that when subjects were provided with unspecific advance information concerning the position of the target, and thus were unable to partially prepare movements prior to the imperative stimulus, a left hand advantage for speed of initiation was obtained. When complete advance information was available, reaction times for the left and right hands were equivalent. The left hand advantage in choice conditions was eliminated when the accuracy of response execution was emphasized and subjects were afforded the opportunity for "on-line" preparation (Experiment 3). These data are discussed in relation to the role of the right hemisphere in the preparation of movement.