Unimanual Tasks Research Articles

Effects of Aerobic Fitness on Aging-Related Changes of Interhemispheric Inhibition and Motor Performance

Physical fitness has been long associated with maintenance and improvement of motor performance as we age. In particular, measures of psychomotor speed and motor dexterity tend to be higher in physically fit aging adults as compared to their sedentary counterparts. Using functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS), we explored the patterns of neural activity that may, in part, account for differences between individuals of varying physical fitness levels. In this study, we enrolled both sedentary and physically fit middle age (40–60) and younger (18–30) adults and measured upper extremity motor performance during behavioral testing. In a follow-up session, we employed TMS and fMRI to assess levels of interhemispheric communication during unimanual tasks. Results show that increased physical fitness is associated with better upper extremity motor performance on distal dexterity assessments and increased levels of interhemispheric inhibition in middle age adults. Further, the functional correlates of changes of ipsilateral activity appears to be restricted to the aging process as younger adults of varying fitness levels do not differ in hemispheric patterns of activity or motor performance. We conclude that sedentary aging confers a loss of interhemispheric inhibition that is deleterious to some aspects of motor function, as early as midlife, but these changes can be mediated by chronic engagement in aerobic exercise.

Memory for Hand-Use Depends on Consistency of Handedness

Individuals who do not consistently use the same hand to perform unimanual tasks (inconsistent-handed) outperform consistent right- and left-handed individuals on tests of episodic memory. We explored whether the inconsistent-hander (ICH) memory advantage extends to memory for unimanual hand use itself. Are ICHs better able to remember which hand they used to perform actions? Opposing predictions are possible, stemming from the finding that some regions of the corpus callosum are larger in ICHs, especially those that connect motor areas. One hypothesis is that greater callosally mediated interhemispheric interaction produces ICHs’ superior retrieval of episodic memories, and this may extend to episodic memories for hand use. Alternatively, we also hypothesized that greater interhemispheric interaction could produce more bilateral activation in motor areas during the performance and retrieval of unimanual actions. This could interfere with ICHs’ ability to remember which hand they used. To test these competing predictions in the current study, consistent- and inconsistent-handers performed unimanual actions, half of which required manipulating objects and half of which did not. Each action was performed four times in one of five conditions that differed in the ratio of left to right hand use: always left (4:0), usually left (3:1), equal (2:2), usually right (1:3), or always right (0:4). We compared consistent- and inconsistent-handers on recall of the left:right ratio for each action. ICHs remembered how they performed actions better than consistent-handers, regardless of ratio. These findings provide another example of superior episodic retrieval in ICHs. We discuss how greater interaction might benefit memory for hand use.

Hand Dominance and Age Have Interactive Effects on Motor Cortical Representations

Older adults exhibit more bilateral motor cortical activity during unimanual task performance than young adults. Interestingly, a similar pattern is seen in young adults with reduced hand dominance. However, older adults report stronger hand dominance than young adults, making it unclear how handedness is manifested in the aging motor cortex. Here, we investigated age differences in the relationships between handedness, motor cortical organization, and interhemispheric communication speed. We hypothesized that relationships between these variables would differ for young and older adults, consistent with our recent proposal of an age-related shift in interhemispheric interactions. We mapped motor cortical representations of the right and left first dorsal interosseous muscles using transcranial magnetic stimulation (TMS) in young and older adults recruited to represent a broad range of the handedness spectrum. We also measured interhemispheric communication speed and bimanual coordination. We observed that more strongly handed older adults exhibited more ipsilateral motor activity in response to TMS; this effect was not present in young adults. Furthermore, we found opposing relationships between interhemispheric communication speed and bimanual performance in the two age groups. Thus, handedness manifests itself differently in the motor cortices of young and older adults and has interactive effects with age.

Subliminal priming and effects of hand dominance

In the masked priming paradigm, motor responses to targets are influenced by previously presented subliminal primes, and are guided by facilitatory and inhibitory mechanisms that depend on prime-target compatibility/duration. In this study, we evaluate subliminal-driven priming in right- and left-handers during unimanual as well as bimanual tasks. The data from the unimanual tasks confirmed that prime-target compatibility affects performance as a function of prime-target duration. In a bimanual setting, the preferred hand benefitted from facilitation in both handedness groups whereas the non-preferred hand showed a positive priming effect only in left-handers. This denotes that left-handers are more susceptible to response activation of either hand. In addition, inhibitory priming had a stronger effect on the non-preferred than preferred hand, independent of handedness group. Overall, the findings suggest that subliminal-driven mechanisms that assist adaptive motor behavior are sensitive not only to extrinsic (task-related) factors such as prime-target compatibility but also to intrinsic (performer-related) factors such as hand dominance. The data further provide support for handedness-specific effects in motor functions and underline a significant role of hand dominance in the control of bimanual actions.

Fixed-Point Drift and Hysteresis in Frequency-Scaled Unimanual Coordination

ABSTRACT Research on human rhythmic coordination has shown that the in-phase and antiphase coordination modes are typically stable and that the coordination of asymmetric effectors frequently exhibits fixed-point drift. The author extended research on symmetry breaking in coordination dynamics by examining a frequency-scaled unimanual pronation-supination task. The results showed symmetry breaking and fixed-point drift, with the radioulnar joint increasingly more phase advanced than the shoulder with increments in movement frequency. Hysteresis was also observed, as the relative phase patterns produced at 3 of the 4 movement frequencies were lower in the upward frequency scaling direction than in the downward direction. These results showed that the dynamic properties of symmetry breaking and fixed-point drift in unimanual pronation-supination movements were consistent with prior research and modeling. The hysteresis effect was explained as potentially being due to the control structures that organize this redundant coordination task.

Is modified constraint-induced movement therapy more effective than bimanual training in improving arm motor function in the subacute phase post stroke? A randomized controlled trial

Objective: To compare the effect of modified constraint-induced movement therapy (mCIMT) to bimanual task-related training for patients in the subacute phase post stroke. Design: A single-blinded randomized controlled trial. Settings: Inpatient and outpatient rehabilitation clinics and the patient’s home. Subjects: Thirty patients in the subacute phase post stroke (2–16 weeks) were randomized to modified constraint-induced movement therapy with an emphasis on unimanual tasks, or bimanual task-related training, emphasizing bimanual tasks. All trained with a therapist 4 hours a week for four weeks, followed by a 2–3 hours daily self-training program. Patients in the modified constraint-induced movement therapy group were supposed to wear a restraining mitt on the unaffected hand for 4 hours a day for four weeks. Main measures: Blinded assessments at pre and post treatment and after three months with Action Research Arm Test as a primary outcome measure, Nine-Hole Peg Test and Motor Activity Log. Results: Power calculations suggested an inclusion of 60 patients, but due to recruitment difficulties the trial was stopped after an interim analysis at 30 patients. There was no difference in change (P > 0.05) between the groups on any of the measures, neither at post treatment nor at follow-up assessments. From pre-intervention to follow-up assessment the modified constraint-induced movement therapy group obtained a mean change score of 17.77 (14.66) on Action Research Arm Test, the bimanual group 15.47 (13.59). Conclusion: Bimanual training was as effective as modified constraint-induced movement therapy in improving arm motor function. Wearing a mitt seems unnecessary for most patients in the subacute phase post stroke when focused affected arm training is provided.

Vision-to-event and movement-to-event coordination in an unimanual circling task

Coordination of actions with events in extracorporeal space is essential for many everyday tasks. In the present study, we investigated how transformations, like in tool use, and varying the spatial context affect action coordination. For this aim, we used a circling task that required participants to coordinate the visual feedback of hand movements with a clockwise circling stimulus (event). The trajectories of stimulus and visual feedback were presented horizontally aligned (group horizontal), within each other (group interleaved) or vertically aligned (group vertical). Within groups, we varied the instructed rotation direction of stimulus and visual feedback (same and different), and y-direction of visual feedback relative to the stimulus (same and different). To dissociate movements and the associated proprioceptive/kinesthetic feedback from visual movement feedback, participants performed the tasks under regular and transformed visual feedback (180° angular shift). Results indicated that action coordination follows the principle of vision-to-event coordination (similar data patterns with regular and transformed feedback), but subtle effects of movement-to-event coordination were also observed (larger difference in performance between same y-direction and different y-direction conditions with regular than with transformed feedback). The presence of a transformation affected performance negatively. The different visual layouts affected the different conditions differentially, pointing to the importance of the visual context. In conclusion, vision-to-event coordination dominates unimanual action coordination. The quality of performance is influenced by perceptual processes based on differential processing of the horizontal and vertical axis, and based on Gestalt principles.

Intended actions and unexpected outcomes: automatic and controlled processing in a rapid motor task

Human action involves a combination of controlled and automatic behavior. These processes may interact in tasks requiring rapid response selection or inhibition, where temporal constraints preclude timely intervention by conscious, controlled processes over automatized prepotent responses. Such contexts tend to produce frequent errors, but also rapidly executed correct responses, both of which may sometimes be perceived as surprising, unintended, or “automatic”. In order to identify neural processes underlying these two aspects of cognitive control, we measured neuromagnetic brain activity in 12 right-handed subjects during manual responses to rapidly presented digits, with an infrequent target digit that required switching response hand (bimanual task) or response finger (unimanual task). Automaticity of responding was evidenced by response speeding (shorter response times) prior to both failed and fast correct switches. Consistent with this automaticity interpretation of fast correct switches, we observed bilateral motor preparation, as indexed by suppression of beta band (15–30 Hz) oscillations in motor cortex, prior to processing of the switch cue in the bimanual task. In contrast, right frontal theta activity (4–8 Hz) accompanying correct switch responses began after cue onset, suggesting that it reflected controlled inhibition of the default response. Further, this activity was reduced on fast correct switch trials suggesting a more automatic mode of inhibitory control. We also observed post-movement (event-related negativity) ERN-like responses and theta band increases in medial and anterior frontal regions that were significantly larger on error trials, and may reflect a combination of error and delayed inhibitory signals. We conclude that both automatic and controlled processes are engaged in parallel during rapid motor tasks, and that the relative strength and timing of these processes may underlie both optimal task performance and subjective experiences of automaticity or control.

Practice Effects on Decreasing and Increasing Force-Control during Periodic Isometric Movements of the Index Finger

The present study examined whether improvement in control while decreasing force to achieve a lower force target would be facilitated by comparison of performance while increasing force to achieve a higher force target. Participants practiced control of isometric force and timing during a unimanual force production task cycling between 5 and 10% of maximum voluntary contraction with a target interval of 500 msec. Although errors and variability of both peak and valley forces and interval decreased during early practice, the valley force was still more inaccurate and variable than the peak force in the final practice. Variabilities of both forces did not decrease when the valley force was synchronized with an audible metronome pulse but did decrease when the peak force was synchronized with it.

Task-dependent effects of interhemispheric inhibition on motor control

Interhemispheric communication consists of a complex balance of facilitation and inhibition that is modulated in a task-dependent manner. However, it remains unclear how individual differences in interhemispheric interactions relate to motor performance. To assess interhemispheric inhibition, we utilized the ipsilateral silent period technique (iSP; evoked by suprathreshold transcranial magnetic stimulation), which elicits inhibition of volitional motor activity. Participants performed three force production tasks: (1) unimanual (right hand) constant force, (2) bimanual constant force, (bimanual simultaneous) and (3) bimanual with right hand constant force and left hand sine wave tracking (bimanual independent). We found that individuals with greater IHI capacity demonstrated reduced mirror EMG activity in the left hand during unimanual right hand contraction. However, these same individuals demonstrated the poorest performance during the bimanual independent force production task. We suggest that a high capacity for IHI from one motor cortex to another can effectively prevent “motor overflow” during unimanual tasks, but it can also limit interhemispheric cooperation during independently controlled bimanual tasks.

Hemispheric lateralization in aging: Interest of the verbal-manual concurrency paradigm

ABSTRACT Introduction: The aim of this study was to evaluate whether the classic asymmetry seen in hemispheric functioning is modified in older adults by using a verbal-manual concurrency task. Method: Thirty-five right-handed participants divided into two groups according to age (15 older participants, mean age: 68 ± 8 years, without cognitive decline and 20 younger participants, mean age: 23 ± 2 years) had to perform a 30-second uni-manual tapping task, in both a single task (tapping alone) and dual task (tapping and performing a letter fluency task together) condition. Results: In younger participants, the letter fluency task disrupted the right hand more than the left hand whereas, in older participants, the letter fluency task disrupted both hands equally. Conclusion: These results should be considered preliminary data using a behavioral dual task condition, which might be useful for studying lateralized hemispheric functioning and the processes of divided attention during aging.

Reversal of handedness effects on bimanual coordination in adults with Down syndrome

Research on unimanual tasks suggested that motor asymmetries between hands may be reduced in people with Down syndrome. Our study examined handedness (as assessed by hand performance) and perceptual-motor integration effects on bimanual coordination. Adults with Down syndrome (13 non-right-handed, 22 right-handed), along with comparison groups of adults (16 non-right-handed, 21 right-handed) and children (15 non-right-handed, 22 right-handed) without Down syndrome, drummed with auditory, verbal and visual instructions. In contrast to handedness effects in the children and adults without Down syndrome, right-handed participants with Down syndrome led more with the left hand, and had lower coordination stability than non-right-handed participants with Down syndrome. The reversed handedness effect during bimanual coordination suggests a complex relationship between handedness and task requirements in adults with Down syndrome.

Design and Control of a Power Assist System for Lifting Objects Based on Human Operator's Weight Perception and Load Force Characteristics

This paper deals with the design and control of a power assist system for lifting objects. It was hypothesized that an operator's perception of weight due to inertial force might be different from the perceived weight due to gravitational force. The system was simulated for different sizes of objects. Results show that an increase in mechanical time constant reduces perceived heaviness and load forces. The results also show the technique for simultaneous optimization of motion and perceived heaviness. Psychophysical studies show that the power assist system reduces the weights of the lifted objects to 40%, 30%, and 25% of the actual weights for unimanual, bimanual, and cooperative lifting tasks, respectively. The studies also show that operators apply 6.30, 6.22, and 6.14 times larger than the actually required load forces for the unimanual, bimanual, and cooperative lifting tasks, respectively. Therefore, a novel control strategy was proposed that reduced the excessive load forces and thus enhanced maneuverability, safety, naturalness, etc., of the system. The feasibility of zero gravity and zero inertia was studied. The operator's load force characteristics in some worst cases were studied. The effects of friction between an object and the operator's hand on weight perception and load forces were also studied. Power-assisted manipulation of objects in harmonic motion was also considered. Finally, it was proposed to use the findings to design power assist systems for lifting heavy objects in industries such as manufacturing, logistics, transport, construction, military and rescue operations, mining, etc., that would enhance interactions with human users.

Motor planning and execution in left- and right-handed individuals during a bimanual grasping and placing task

The issue of handedness has been the topic of great interest for researchers in a number of scientific domains. It is typically observed that the dominant hand yields numerous behavioral advantages over the non-dominant hand during unimanual tasks, which provides evidence of hemispheric specialization. In contrast to advantages for the dominant hand during motor execution, recent research has demonstrated that the right hand has advantages during motor planning (regardless of handedness), indicating that motor planning is a specialized function of the left hemisphere. In the present study we explored hemispheric advantages in motor planning and execution in left- and right-handed individuals during a bimanual grasping and placing task. Replicating previous findings, both motor planning and execution was influenced by object end-orientation congruency. In addition, although motor planning (i.e., end-state comfort) was not influenced by hand or handedness, motor execution differed between left and right hand, with shorter object transport times observed for the left hand, regardless of handedness. These results demonstrate that the hemispheric advantages often observed in unimanual tasks do not extend to discrete bimanual tasks. We propose that the differences in object transport time between the two hands arise from overt shifting visual fixation between the two hands/objects.

The relationship between end-state comfort effects and memory performance in serial and free recall

In two experiments we examined the relationship between end-state comfort effects and memory performance in serial and free recall. In Experiment 1, 24 university students completed a bimanual end-state comfort task and a memory task. Participants viewed a series of 11 letters, then performed the bimanual overturned glass task in which they simultaneously moved two glasses from an upper shelf to a lower shelf, and then recalled the letters in either serial or free recall conditions. Memory recall was evaluated based on the presence or absence of primacy and recency effects. The end-state comfort effect was assessed by the percentage of initial hand positions that allowed the hands to end up in a comfortable thumbs-up posture. The end-state comfort effect was present in both memory conditions. The results revealed the disappearance of the recency effect in serial and free recall, although the effect was much stronger during serial recall. In Experiment 2, we asked whether simpler motor tasks might bring back the recency effect. Forty-eight participants completed either a bimanual or unimanual task that involved moving non-descript plastic cylinder(s) from an upper shelf to a lower shelf. An unexpected finding was that even after performance of the simpler motor tasks, the recency effect was still absent. The disappearance of the recency effect, regardless of the complexity of the motor task, suggests a reciprocal influence of physical action and cognitive processes, which we interpret as a basic concurrence cost.

Typical and atypical (cerebral palsy) development of unimanual and bimanual grasp planning

In the present study we tested 13 children with cerebral palsy (CP) and 24 typically developing children (7–12 years old) in a unimanual and bimanual motor planning task. We focused on two research questions: (1) How does motor planning develop in children with and without CP? and (2) Is motor planning facilitated when the task is performed with both hands? Participants had to grasp one or two vertical oriented cylinder(s) and transport it/them to a platform that had different heights. As a measure of motor planning, we registered the height at which participants grasped the cylinder. Here, anticipation of grasp height upon the height of the upcoming target(s) is reflective of proper forward motor planning as it leads to a comfortable posture at the end of the task. In the unimanual task the typically developing children showed a significant grasp height effect, which increased with age. In contrast, no grasp height effect, or age related changes therein were found for the children with CP, suggesting a compromised development of motor planning in these children. Interestingly, when children had to transport one cylinder to a high shelf and one cylinder to a low shelf, the more affected hand of the CP children clearly anticipated the grasp height to the upcoming target height. The less affected hand did not show such anticipation. Taken collectively, these findings suggest a delayed or compromised development of motor planning in children with CP compared to typically developing children. At the same time, the facilitated motor planning of the more affected arm in the bimanual task offers a valuable entry point for intervention to improve motor planning in CP.

Frequency-induced changes in interlimb interactions: Increasing manifestations of closed-loop control

In bimanual coordination, interactions between the limbs result in attraction to in-phase and antiphase coordination. Increasing movement frequency leads to decreasing stability of antiphase coordination, often resulting in a transition to the more stable in-phase pattern. It is unknown, however, how this frequency-induced loss of stability is engendered in terms of the interlimb interactions underwriting bimanual coordination. The present study was conducted to help resolve this issue. Using an established method (based on comparison of various unimanual and bimanual tasks involving both passive and active movements), three sources of interlimb interaction were dissociated: (1) integrated timing of feedforward signals, (2) afference-based correction of relative phase errors, and (3) phase entrainment by contralateral afference. Results indicated that phase entrainment strength remained unaffected by frequency and that the stabilizing effects of error correction and integrated timing decreased with increasing frequency. Their contributions, however, reflected an interesting interplay as frequency increased. For moderate frequencies coordinative stability was predominantly secured by integrated timing processes. However, at high frequencies, the stabilization of the antiphase pattern required combined contributions of both integrated timing and error correction. In sum, increasing frequency was found to induce a shift from predominantly open-loop control to more closed-loop control. The results may be accounted for by means of an internal forward model for sensorimotor integration in which the sensory signals are compared to values predicted on the basis of efference copies.

Glioblastoma multiforme at the corpus callosum with spinal leptomeningeal metastasis

Glioblastoma multiforme (GBM) often occurs in the supratentorial white matter including corpus callosum. However, spinal leptomeningeal metastasis in cases of supratentorial GBM has been reported to be rare and there is usually a long interval between the cerebral lesion and the spinal seeding. We report here a case of GBM at the corpus callosum and other parts of the brain with simultaneous manifestation of spinal leptomeningeal seeding. The patient exhibited an abnormal motor behavior of the left hand as mirror movement when the right hand was performing a unimanual task (diagonistic dyspraxia) which is a sign of lesion of the posterior part and splenium of the corpus callosum. There were also signs of peripheral nerve or nerve root involvement suggestive of spinal metastasis without any sensory symptoms. He died 3 months after the onset of the symptoms confirming the poor prognosis and short survival time in cases with spinal leptomeningeal metastasis reported previously. The cerebral GBM with spinal seeding was disclosed at autopsy.

Cortical and behavioral adaptations in response to short-term inphase versus antiphase bimanual movement training

Bimanual movement training (BMT) may be an effective rehabilitative protocol for movement-related deficits following a stroke; however, it is unclear how varying types of BMT induce cortical adaptations in the healthy population. Moreover, we lack a methodology to measure cortical adaptations in response to modes of movement training. Therefore, the present study measured the cued movement-related potential (MRP) to investigate cortical adaptations during cued inphase versus antiphase BMT that transferred to a unimanual task and how cortical modulations related to behavior. Three specific hypotheses were investigated: (1) cued inphase BMT would induce cortical adaptations within regions subserving motor preparation and movement execution, (2) repetitive cued unimanual training would induce cortical activity modulations associated with motor execution, and (3) increased cortical activity would be associated with enhanced performance. On three separate days, EEG was recorded from 22 electrodes during three types of cued movement training: inphase BMT, antiphase BMT and repetitive unimanual movement, in addition to pre- and post-training unimanual movement trials involving cued right wrist flexion. The MRP was measured for each repetition during each trial. Results showed a significant training-related increase in preparatory activation correlated with a behavioral enhancement following cued inphase BMT. This effect was not attributable to a change in arousal. No significant training-related modulation occurred in response to cued antiphase BMT or repetitive unimanual movement training. These results suggest that cortical adaptations in relation to the preparation of a cued movement enhance in response to cued inphase BMT, and the MRP is an effective measurement tool to assess training-related adaptations in response to inphase BMT specifically.

Manipulation of a fragile object

We investigated strategies of adjustments in kinetic and kinematic patterns, and in multi-digit synergies during quick vertical transport of an instrumented handle that collapsed when the grasping force exceeded a certain magnitude (quantified with a fragility index). The collapse threshold of the object was set using a novel electromagnetic device. Moving a fragile object is viewed as a task with two constraints on the grip force defined by the slipping and crushing thresholds. When moving more fragile objects, subjects decreased object peak acceleration, increased movement time, showed a drop in the safety margin (SM) (extra force over the slipping threshold), and showed a tendency toward violating the minimum-jerk criterion. Linear regression analysis of grip force against load force has shown tight coupling between the two with a decline in the coefficient of determination with increased fragility index. The SM was lower in bimanual tasks, compared to unimanual tasks, for both fragile and non-fragile objects. Two novel indices have been introduced and studied, the SM due to fragility and the drop-crush index. Both indices showed a decrease with increased object fragility. Changes in the drop-crush index showed that the subjects would rather crush the fragile objects as opposed to dropping them, possibly reflecting the particular experimental procedure. We did not find differences between the performance indices of the dominant and non-dominant hand thus failing to support the recently formulated dominance hypothesis. The synergies stabilizing grip force were quantified at two levels of an assumed two-level control hierarchy using co-variation indices between elemental variables across trials. There were strong synergies at the upper level of the hierarchy (the task is shared between the opposing groups of digits) that weakened with an increase in object fragility. At the lower level (action of an effector is shared among the four fingers), higher fragility led to higher synergy indices. Analysis of force variance showed that an increase in object fragility was accompanied by exploring a smaller range of equivalent combinations of elemental variables. The additional constraint imposed by high fragility facilitated synergies at the lower level of the hierarchy, while there was evidence for a trade-off between synergies at the two levels.