Neural Oscillations and Functional Significances for Prioritizing Dual-Task Walking in Parkinson's Disease.

Background: Task prioritization involves allocating brain resources in a dual-task scenario, but the mechanistic details of how prioritization strategies affect dual-task walking performance for Parkinson's disease (PD) are little understood. Objective: We investigated the performance benefits and corresponding neural signatures for people with PD during dual-task walking, using gait-prioritization (GP) and manual-prioritization (MP) strategies. Methods: Participants (N = 34) were asked to hold two inter-locking rings while walking and to prioritize either taking big steps (GP strategy) or separating the two rings (MP strategy). Gait parameters and ring-touch time were measured, and scalp electroencephalograph was performed. Results: Compared with the MP strategy, the GP strategy yielded faster walking speed and longer step length, whereas ring-touch time did not significantly differ between the two strategies. The MP strategy led to higher alpha (8-12 Hz) power in the posterior cortex and beta (13-35 Hz) power in the left frontal-temporal area, but the GP strategy was associated with stronger network connectivity in the beta band. Changes in walking speed and step length because of prioritization negatively correlated with changes in alpha power. Prioritization-related changes in ring-touch time correlated negatively with changes in beta power but positively with changes in beta network connectivity. Conclusions: A GP strategy in dual-task walking for PD can enhance walking speed and step length without compromising performance in a secondary manual task. This strategy augments attentional focus and facilitates compensatory reinforcement of inter-regional information exchange.

Attentional focus effect on dual-task walking in Parkinson's disease with and without freezing of gait.

In Parkinson's disease, the optimal attentional focus strategy for dual-task walking may vary with freezing of gait (FOG), due to different severities of impaired automaticity. The study aimed to investigate (i) the immediate effect of attentional focus on dual-task walking in participants with and without FOG, and (ii) the training effect of attentional focus on walking, FOG, and falls. In experiment 1, FOG and non-FOG groups (16 participants each) performed a dual-task of holding two interlocking rings apart while walking, either without attention instruction or with instructions to focus attention internally or externally. Gait parameters and ring-touching times were measured. In experiment 2, 30 participants with FOG were randomized to 6 weeks of dual-task training with internal-focus or external-focus instruction. Before and after training, we recorded timed up-and-go (TUG) and TUG dual-task (TUGdt) in on-medication and off-medication states, and the numbers of FOG episodes and falls. The non-FOG group showed less step length variability and shorter ring-touching times with external-focus. The FOG group showed less step length variability, less cadence, increased gait velocity, and longer step lengths with internal-focus compared to external-focus and no-focus instructions. Both internal-focus and external-focus training reduced FOG and falls after intervention, but only internal-focus training reduced TUG and TUGdt in both on-medication and off-medication states. Our findings suggest external-focus would enhance walking automaticity and the concurrent task accuracy for non-freezers, whereas for freezers, internal-focus could increase gait stability and lead to a more positive effect on improving locomotion control and reducing falling risk.

Dual-task walking improvement with enhanced kinesthetic awareness in Parkinson's disease with mild gait impairment: EEG connectivity and clinical implication.

Due to basal ganglia dysfunction, short step length is a common gait impairment in Parkinson's disease (PD), especially in a dual-task walking. Here, we use electroencephalography (EEG) functional connectivity to investigate neural mechanisms of a stride awareness strategy that could improve dual-task walking in PD. Eighteen individuals with PD who had mild gait impairment walked at self-paced speed while keeping two interlocking rings from touching each other. During the dual-task walking trial, the participants received or did not receive awareness instruction to take big steps. Gait parameters, ring-touching time, and EEG connectivity in the alpha and beta bands were analyzed. With stride awareness, individuals with PD exhibited greater gait velocity and step length, along with a significantly lower mean EEG connectivity strength in the beta band. The awareness-related changes in the EEG connectivity strength of the beta band positively correlated with the awareness-related changes in gait velocity, cadence, and step length, but negatively correlated with the awareness-related change in step-length variability. The smaller reduction in beta connectivity strength was associated with greater improvement in locomotion control with stride awareness. This study is the first to reveal that a stride awareness strategy modulates the beta band oscillatory network and is related to walking efficacy in individuals with PD in a dual-task condition.

Effects of Upper Trapezius Myofascial Trigger Points on Scapular Kinematics and Muscle Activation in Overhead Athletes.

Prolonged overactivity of the upper trapezius muscle with myofascial trigger points might cause muscle fatigue and subsequently change scapular kinematics and associated muscular activities. Scapular kinematics and associated muscular activities were investigated in 17 overhead athletes with upper trapezius myofascial trigger points and 17 controls before and after a fatigue task. Participants performed a fatigue task requiring sustained isometric scapular elevation. The outcomes included scapular kinematics (upward/downward rotation, external/internal rotation, posterior/anterior tilt) that were tracked by the Polhemus FASTRAK (Polhemus Inc., Colchester, VT, USA) system with Motion Monitor software and muscular activities (upper trapezius, lower trapezius and serratus anterior) that were collected at 1000 Hz per channel using a 16-bit analog-to-digital converter (Model MP 150, Biopac systems Inc., CA, USA) with pairs of silver chloride circular surface electrodes (The Ludlow Company LP, Chocopee, MA) during arm elevation. Mixed ANOVAs were conducted to characterize the outcomes with and without a fatigue task in participants with myofascial trigger points. Decreased scapular posterior tipping during 90 degrees of arm raising/lowering (effect sizes of 0.51 and 0.59) was likely to be elicited by the scapular elevation fatigue task in the presence of myofascial trigger points. Activity of the lower trapezius was higher in the myofascial trigger point group (6.2%, p = 0.036) than in the control group. Following the fatigue task, both groups showed increased activity in the upper trapezius (9.0%, p = 0.009) during arm lowering and in the lower trapezius (2.7%, p < 0.01) during arm raising and lowering. Decreased scapular posterior tipping during 90 degrees of arm raising/lowering after a fatigue task may lead to impingement. We found that the presence of upper trapezius myofascial trigger points in amateur overhead athletes was related to impaired scapular kinematics and associated muscular activities during arm elevation after a fatigue task, especially the decreased scapular tipping during 90 degrees of raising/lowering.

A randomized controlled trial of scapular exercises with electromyography biofeedback in oral cancer patients with accessory nerve dysfunction.

PURPOSE: This study aims to investigate the effects of electromyography (EMG) biofeedback on scapular positions and muscle activities during scapular-focused exercises in oral cancer patients with accessory nerve dysfunction. METHODS: Twenty-four participants were randomly allocated to the motor-control with biofeedback group (N = 12) or the motor-control group (N = 12) immediately after neck dissection. Each group performed scapular-focused exercises with conscious control of scapular orientation for 3 months. EMG biofeedback of upper trapezius (UT), middle trapezius (MT), and lower trapezius (LT) was provided in the motor-control with biofeedback group. Scapular symmetry measured by modified lateral scapular slide test; shoulder pain; active range of motion (AROM) of shoulder abduction; upper extremity function; maximal isometric muscle strength of UT, MT, and LT; and muscle activities during arm elevation/lowering in the scapular plane were evaluated at baseline and the end of the intervention. RESULTS: After the 3-month intervention, only the motor-control with biofeedback group showed improving scapular symmetry. Although both groups did not show significant improvement in shoulder pain, increased AROM of shoulder abduction and muscle strength of the UT and MT were observed in both groups. In addition, only the motor-control with biofeedback group had improved LT muscle strength, upper extremity function, and reduced UT and MT muscle activations during arm elevation/lowering. CONCLUSIONS: Early interventions for scapular control training significantly improved shoulder mobility and trapezius muscle strength. Furthermore, by adding EMG biofeedback to motor-control training, oral cancer patients demonstrated greater effectiveness in stabilizing scapular position, muscle efficiency, and upper extremity function than motor-control training alone. TRIAL REGISTRATION: Institutional Review Board: This study was approved by the Chang Gung Medical Foundation Institutional Review Board (Approval No: 201901788A3. Approval Date: 2 January, 2020). CLINICAL TRIAL REGISTRATION: This trial was registered at ClinicalTrials.gov (ClinicalTrials.gov ID: NCT04476004. Initial released Date: 16 July, 2020).

Effects of task prioritization on a postural-motor task in early-stage Parkinson's disease: EEG connectivity and clinical implication.

Appropriate attentional resource allocation could minimize exaggerated dual-task interference due to basal ganglia dysfunction in Parkinson's disease (PD). Here, we assessed the electroencephalography (EEG) functional connectivity to investigate how task prioritization affected posture-motor dual-tasks in PD. Sixteen early-stage PD patients and 16 healthy controls maintained balance in narrow stance alone (single-posture task) or while separating two interlocking rings (postural dual-task). The participants applied a posture-focus or supraposture-focus strategy in the postural dual-task. Postural sway dynamics, ring-touching time, and scalp EEG were analyzed. Both groups exhibited smaller postural sway size, postural determinism, and ring-touching time with the supraposture-focus versus posture-focus strategy. PD patients exhibited higher mean inter-regional connectivity strength than control subjects in both single and dual-task postural conditions. To cope with dual-task interference, PD patients increased inter-regional connectivity (especially with the posture-focus strategy), while control subjects reduced inter-regional connectivity. The difference in mean connectivity strength between the dual-task condition with supraposture-focus and single-posture condition was negatively correlated to the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS) part III total scores and hand-related sub-scores. Our findings suggest differential task prioritization effects on dual-task performance and cortical reorganization between early-stage PD and healthy individuals. Early-stage PD patients are advocated to use a supraposture-focus strategy during a postural dual-task. In addition, with a supraposture-focus strategy, PD patients with mild motor severity could increase compensatory inter-regional connectivity to cope with dual-task interference.

Glenohumeral Internal Rotation Deficit on Pitching Biomechanics and Muscle Activity.

To characterize the scapular pitching biomechanics in symptomatic GIRD pitchers (SG) compared to asymptomatic GIRD (ASG) and healthy pitchers. The scapular kinematics and associated muscle activities during pitching were recorded in 33 high school pitchers. Compared to healthy, GIRD pitchers had less scapular posterior tilt in each pitching event (average difference, AD=14.4°, p<0.01) and ASG demonstrated less scapular upward rotation at ball release (AD=12.8°, p<0.01) and greater muscle activity in the triceps brachii in the early-cocking phase (AD=9.9%, p=0.015) and in the serratus anterior in the late-cocking phase (AD=30.8%, p<0.01). Additionally, SG had less muscular activity on triceps brachii in the acceleration phase and serratus anterior in the cocking phase (AD=37.8%, p=0.016; AD=15.5%, p<0.01, respectively) compared to ASG. GIRD pitchers exhibited less scapular posterior tilt during pitching, which may cause impingement. Since tightness of the anterior shoulder is a common cause of inadequacy of posterior tilt during arm elevation, stretching exercise of the anterior shoulder is recommended. Given the inadequate recruitment during pitching in the GIRD pitchers, symptoms may develop following potential impingement.

Effects of Conscious Control of Scapular Orientation in Oral Cancer Survivors With Scapular Dyskinesis: A Randomized Controlled Trial.

OBJECTIVES: Spinal accessory nerve dysfunction is one of the complications of neck dissection in patients with oral cancer. This study aimed to explore the effects of long-term scapular-focused exercises and conscious control of scapular orientation on scapular movement and quality of life (QoL). METHODS: This study was a randomized controlled trial with concealed allocation, assessor blinding, and intention-to-treat analysis. Thirty-six patients with oral cancer were randomly allocated to the motor-control group (scapular-focused exercise + conscious control of scapular orientation) or the regular-exercise group (scapular-focused exercises only). Both groups received conventional physical therapy after neck dissection for 3 months. Shoulder pain intensity, active range of motion (AROM) of shoulder abduction, scapular muscle strength and activity under maximal voluntary isometric contraction (MVIC), scapular muscle activity when performing scapular movements, and QoL were measured at baseline, 1 month after the start of the intervention, and the end of the intervention. RESULTS: Both groups showed significant improvement in all outcomes except shoulder pain intensity. After the 3-month intervention, the motor-control group had more significant improvement in AROM of shoulder abduction with a 19° difference (95% CI: 10-29, P < .001), muscle strength of upper trapezius with an 11 N difference (95% CI: 2-20; P = .021), and QoL than the regular-exercise group. When performing shoulder horizontal adduction and flexion, the relative value (%MVIC) of serratus anterior was smaller in the motor-control group with a 106%MVIC difference (95% CI: 7-205, P = .037). CONCLUSIONS: Scapular-focused exercises have promising effects on spinal accessory nerve dysfunction. Combining scapular-focused exercises with conscious control of scapular orientation has more remarkable benefits on AROM of shoulder abduction, UT muscle strength, and muscle activation pattern than the scapular-focused exercises alone. Conscious control of scapular orientation should be considered to integrate into scapular-focused exercises in patients with oral cancer and scapular dyskinesis.Trial registry name and URL, and registration number: ClinicalTrials.gov (URL: https://clinicaltrials.gov; Approval No: NCT03545100).

Motor control integrated into muscle strengthening exercises has more effects on scapular muscle activities and joint range of motion before initiation of radiotherapy in oral cancer survivors with neck dissection: A randomized controlled trial.

BACKGROUND: Accessory nerve shoulder dysfunction is common after neck dissection in oral cancer survivors. This study aimed to investigate the short-term effects of scapular muscle strengthening exercises with motor-control techniques on neck dissection-related shoulder dysfunction in oral cancer survivors before the initiation of radiotherapy. METHODS: Thirty-eight participants were randomly allocated into the motor-control and regular-exercise groups. Each group received conventional physical therapy and specific scapular muscle strengthening exercises for 1 month immediately after neck dissection. Motor control techniques were integrated with scapular strengthening exercises for the motor-control group. Shoulder pain, active range of motion (AROM) of shoulder abduction, and scapular muscle activities including upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) when performing maximal voluntary isometric contraction (MVIC) and scapular muscle exercises were evaluated at baseline and after 1 month of training. RESULTS: Both groups reduced shoulder pain and increased muscle activity of maximum voluntary isometric contraction (MVIC) of each muscle after the intervention. Increased AROM of shoulder abduction was only observed in the motor-control group (95% CI 3.80 to 20.51, p = 0.004). Relative to baseline evaluation, muscle activities of UT decreased in the motor-control group when performing shoulder shrug with 1-kg weight (95% CI -33.06 to -1.29, p = 0.034). Moreover, the SA activity decreased in the motor-control group (95% CI -29.73 to -27.68, p<0.001) but increased in the regular-exercise group (95% CI 28.16 to 30.05, p<0.001) when performing shoulder horizontal adduction and flexion. CONCLUSION: Early strengthening exercise with motor control techniques has greater benefits for improving AROM of shoulder abduction, muscle economy, and reducing compensatory scapular muscle activities in patients with neck dissection-related shoulder dysfunction before the initiation of radiotherapy.

Attentional Resource Associated With Visual Feedback on a Postural Dual Task in Parkinson's Disease.

BACKGROUND: Restricted attentional resource and central processing in patients with Parkinson's disease (PD) may reduce the benefit of visual feedback in a dual task. OBJECTIVES: Using brain event-related potentials (ERPs), this study aims to investigate the neural mechanisms of posture visual feedback and supraposture visual feedback during performing of a posture-motor dual task. METHODS: Eighteen patients with PD and 18 healthy controls stood on a mobile platform (postural task) and executed a manual force-matching task (suprapostural task) concurrently with provided visual feedback of platform movement (posture-feedback condition) or force output (force-feedback condition). The platform movement, force-matching performance, and ERPs (P1, N1, and P2 waves) were recorded. RESULTS: Both PD and control groups had superior force accuracy in the force-feedback condition. Decreased postural sway by posture-feedback was observed in healthy controls but not in PD. Force-feedback led to a greater frontal area N1 peak in PD group but smaller N1 peaks in control group. In addition, force-feedback led to smaller P2 peaks of the frontal and sensorimotor areas among PD patients but greater P2 peaks of the sensorimotor and parietal-occipital areas among healthy controls. However, P1 modulations was present only in healthy controls. CONCLUSIONS: Force-feedback had positive effect on force accuracy in both PD and healthy individuals; however, the beneficial effect of posture-feedback on posture balance is not observed in PD. These findings are the first to suggest that PD could recruit more attentional resources in dual-task preparation to enhance suprapostural accuracy and avoid degrading postural stability by supraposture visual feedback.

The Effects of Task Prioritization on Dual-Tasking Postural Control in Patients With Parkinson Disease Who Have Different Postural Impairments.

OBJECTIVE: To investigate the effect of task prioritization on dual-task control in Parkinson disease (PD) associated with different postural impairments. DESIGN: Cross-sectional study. Participants were instructed to keep 2 interlocking rings apart and maintain balance in a tandem stance. Attention was focused on either stance stability (posture-focus strategy) or the interlocking rings (supraposture-focus strategy). SETTING: University research laboratory. PARTICIPANTS: Fifteen patients with PD and less postural impairment and 15 patients with PD and more postural impairment (N=30). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Postural sway, postural determinism (%DET), ankle co-contraction, and ring-touching time. RESULTS: In the less-impairment group, the supraposture-focus strategy provided smaller postural sway and postural %DET compared with the posture-focus strategy. In the more-impairment group, task prioritization showed lower effect on both postural sway and postural %DET. The supraposture-focus strategy led to less ankle co-contraction than the posture-focus strategy in the more-impairment group, but task prioritization did not affect ankle co-contraction in the less-impairment group. In both groups, the supraposture-focus strategy led to less ring-touching time than the posture-focus strategy. CONCLUSIONS: The supraposture-focus strategy provided better dual-task control than the posture-focus strategy in both PD groups. In the less-impairment group, the supraposture-focus strategy enhanced postural automaticity and postural stability. In the more-impairment group, the supraposture-focus strategy reduced ankle stiffness, owing to reduced muscle co-contraction.

H-reflex in abductor hallucis and postural performance between flexible flatfoot and normal foot.

OBJECTIVE: Morphological changes of the abductor hallucis muscle (AbH) in flexible flatfoot (FF) individuals influence regulations of the medial longitudinal arch (MLA). Prolonged and repeated stretching of AbH in flexible flatfoot may cause changes in muscle reflex properties and further influence postural performance. However, AbH muscle reflex under different postural conditions have never been examined. The purpose of this study was to investigate differences in AbH H-reflex and postural performance between individuals with normal foot (NF) alignment and FF under prone, double-leg stance (DLS), and single-leg stance (SLS) conditions. DESIGN: Cross-sectional study. SETTING: University laboratory. PARTICIPANTS: Individuals with FF (n = 12) and NF (n = 12). MAIN OUTCOME MEASURES: AbH H-reflex, AbH EMG and center of pressure (CoP) displacement. RESULTS: Under all postural conditions, AbH H-reflex was significantly lower in the FF group (P < .05). Under the SLS condition, AbH EMG was significantly higher in the FF group (P < .05), and CoP displacement for the medial-lateral and anterior-posterior directions were significantly higher in the FF group (P < .05). CONCLUSIONS: With increased postural demand, FF individuals maintained their postural stability by recruiting greater AbH activities than through automatic stretch reflex, but FF individuals still showed inferior posture stability.

Neuronal Responses to a Postural Dual-Task With Differential Attentional Prioritizations: Compensatory Resource Allocation With Healthy Aging.

OBJECTIVES: Restricted central processing in older adults prevents optimization of a dual task with a flexible prioritization strategy. This study investigated the neural mechanisms of task-priority in young and older adults when performing a posture-motor dual-task. METHOD: Sixteen healthy young and 16 older adults performed a force-matching task on a mobile-platform under posture-focus (PF) and supraposture-focus (SF) conditions. The platform movement, force-matching performance, and event-related potentials in the preparatory period were recorded. RESULTS: For the elders, the postural stability and force-matching accuracy using the PF strategy were inferior to those using the SF strategy; whereas, the dual-task performances of the young adults were less affected by the prioritization. Only the elders exhibited the P1 wave, with the PF strategy associated with a smaller P1 and larger P1 than the SF strategy in the sensorimotor-parietal and right frontotemporal areas, respectively. The PF strategy also led to a larger P2 wave in the right frontotemporal area of elders, but a greater P2 wave in the sensorimotor-parietal area of young adults. DISCUSSION: For both prioritization strategies, older adults entailed a longer preparatory process than younger adults. Dual-task performance of older adults was more vulnerable to PF strategy, underlying compensatory resource allocation in the preparatory period for resolution of dual-task interference due to degenerated frontal function.

Progressive conscious control of scapular orientation with video feedback has improvement in muscle balance ratio in patients with scapular dyskinesis: a randomized controlled trial.

BACKGROUND: Video feedback (VF) can guide patients to consciously control scapular orientation without inappropriate substitution. This study investigated whether progressive conscious control with VF improves scapular muscle activation and movements during arm elevation in patients with subacromial impingement and scapular dyskinesis. METHODS: The study recruited 38 amateur overhead athletes with subacromial impingement and scapular medial border prominence who were randomly assigned to the VF or control group. The participants in both groups controlled the scapular position and progressively practiced from 0° to 45° and from 0° to 90° of arm elevation. Participants in the VF group also controlled the scapular position with a video presentation of the scapula on a screen. We investigated the scapular kinematics, muscle activation, and balance ratio for outcome collection in the preintervention and postintervention conditions with and without VF conditions. RESULTS: Decreased upper trapezius (UT) activation (3%-13%, P < .0083), increased lower trapezius (LT) activation (3%-17%, P < .0083), restored UT/LT ratios (0.67-3.13, P < .0083), and decreased scapular internal rotation (1.8°-6.1°, P < .003) relative to the preintervention condition were demonstrated in the 2 postintervention conditions in both groups. The VF group also demonstrated decreased UT/serratus anterior ratios (0.21-0.30, P < .0083) in 2 postintervention conditions relative to the preintervention condition. CONCLUSIONS: The progressive control of scapular orientation with or without VF can be used to reduce the UT/LT ratio and improve scapular internal rotation during arm elevation. Control training with VF can further decrease the UT/serratus anterior ratio.

Improving Dual-Task Control With a Posture-Second Strategy in Early-Stage Parkinson Disease.

OBJECTIVE: To examine the task prioritization effects on postural-suprapostural dual-task performance in patients with early-stage Parkinson disease (PD) without clinically observed postural symptoms. DESIGN: Cross-sectional study. Participants performed a force-matching task while standing on a mobile platform, and were instructed to focus their attention on either the postural task (posture-first strategy) or the force-matching task (posture-second strategy). SETTING: University research laboratory. PARTICIPANTS: Individuals (N=16) with early-stage PD who had no clinically observed postural symptoms. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Dual-task change (DTC; percent change between single-task and dual-task performance) of posture error, posture approximate entropy (ApEn), force error, and reaction time (RT). Positive DTC values indicate higher postural error, posture ApEn, force error, and force RT during dual-task conditions compared with single-task conditions. RESULTS: Compared with the posture-first strategy, the posture-second strategy was associated with smaller DTC of posture error and force error, and greater DTC of posture ApEn. In contrast, greater DTC of force RT was observed under the posture-second strategy. CONCLUSIONS: Contrary to typical recommendations, our results suggest that the posture-second strategy may be an effective dual-task strategy in patients with early-stage PD who have no clinically observed postural symptoms in order to reduce the negative effect of dual tasking on performance and facilitate postural automaticity.

Age-Related Differences in Reorganization of Functional Connectivity for a Dual Task with Increasing Postural Destabilization.

The aged brain may not make good use of central resources, so dual task performance may be degraded. From the brain connectome perspective, this study investigated dual task deficits of older adults that lead to task failure of a suprapostural motor task with increasing postural destabilization. Twelve younger (mean age: 25.3 years) and 12 older (mean age: 65.8 years) adults executed a designated force-matching task from a level-surface or a stabilometer board. Force-matching error, stance sway, and event-related potential (ERP) in the preparatory period were measured. The force-matching accuracy and the size of postural sway of the older adults tended to be more vulnerable to stance configuration than that of the young adults, although both groups consistently showed greater attentional investment on the postural task as sway regularity increased in the stabilometer condition. In terms of the synchronization likelihood (SL) of the ERP, both younger and older adults had net increases in the strengths of the functional connectivity in the whole brain and in the fronto-sensorimotor network in the stabilometer condition. Also, the SL in the fronto-sensorimotor network of the older adults was greater than that of the young adults for both stance conditions. However, unlike the young adults, the older adults did not exhibit concurrent deactivation of the functional connectivity of the left temporal-parietal-occipital network for postural-suprapostural task with increasing postural load. In addition, the older adults potentiated functional connectivity of the right prefrontal area to cope with concurrent force-matching with increasing postural load. In conclusion, despite a universal negative effect on brain volume conduction, our preliminary results showed that the older adults were still capable of increasing allocation of neural sources, particularly via compensatory recruitment of the right prefrontal loop, for concurrent force-matching under the challenging postural condition. Nevertheless, dual-task performance of the older adults tended to be more vulnerable to postural load than that of the younger adults, in relation to inferior neural economy or a slow adaptation process to stance destabilization for scant dissociation of control hubs in the temporal-parietal-occipital cortex.

Improving posture-motor dual-task with a supraposture-focus strategy in young and elderly adults.

In a postural-suprapostural task, appropriate prioritization is necessary to achieve task goals and maintain postural stability. A "posture-first" principle is typically favored by elderly people in order to secure stance stability, but this comes at the cost of reduced suprapostural performance. Using a postural-suprapostural task with a motor suprapostural goal, this study investigated differences between young and older adults in dual-task cost across varying task prioritization paradigms. Eighteen healthy young (mean age: 24.8 ± 5.2 years) and 18 older (mean age: 68.8 ± 3.7 years) adults executed a designated force-matching task from a stabilometer board using either a stabilometer stance (posture-focus strategy) or force-matching (supraposture-focus strategy) as the primary task. The dual-task effect (DTE: % change in dual-task condition; positive value: dual-task benefit, negative value: dual-task cost) of force-matching error and reaction time (RT), posture error, and approximate entropy (ApEn) of stabilometer movement were measured. When using the supraposture-focus strategy, young adults exhibited larger DTE values in each behavioral parameter than when using the posture-focus strategy. The older adults using the supraposture-focus strategy also attained larger DTE values for posture error, stabilometer movement ApEn, and force-matching error than when using the posture-focus strategy. These results suggest that the supraposture-focus strategy exerted an increased dual-task benefit for posture-motor dual-tasking in both healthy young and elderly adults. The present findings imply that the older adults should make use of the supraposture-focus strategy for fall prevention during dual-task execution.

An Increase in Postural Load Facilitates an Anterior Shift of Processing Resources to Frontal Executive Function in a Postural-Suprapostural Task.

Increase in postural-demand resources does not necessarily degrade a concurrent motor task, according to the adaptive resource-sharing hypothesis of postural-suprapostural dual-tasking. This study investigated how brain networks are organized to optimize a suprapostural motor task when the postural load increases and shifts postural control into a less automatic process. Fourteen volunteers executed a designated force-matching task from a level surface (a relative automatic process in posture) and from a stabilometer board while maintaining balance at a target angle (a relatively controlled process in posture). Task performance of the postural and suprapostural tasks, synchronization likelihood (SL) of scalp EEG, and graph-theoretical metrics were assessed. Behavioral results showed that the accuracy and reaction time of force-matching from a stabilometer board were not affected, despite a significant increase in postural sway. However, force-matching in the stabilometer condition showed greater local and global efficiencies of the brain networks than force-matching in the level-surface condition. Force-matching from a stabilometer board was also associated with greater frontal cluster coefficients, greater mean SL of the frontal and sensorimotor areas, and smaller mean SL of the parietal-occipital cortex than force-matching from a level surface. The contrast of supra-threshold links in the upper alpha and beta bands between the two stance conditions validated load-induced facilitation of inter-regional connections between the frontal and sensorimotor areas, but that contrast also indicated connection suppression between the right frontal-temporal and the parietal-occipital areas for the stabilometer stance condition. In conclusion, an increase in stance difficulty alters the neurocognitive processes in executing a postural-suprapostural task. Suprapostural performance is not degraded by increase in postural load, due to (1) increased effectiveness of information transfer, (2) an anterior shift of processing resources toward frontal executive function, and (3) cortical dissociation of control hubs in the parietal-occipital cortex for neural economy.

Neural Correlates of Task Cost for Stance Control with an Additional Motor Task: Phase-Locked Electroencephalogram Responses.

With appropriate reallocation of central resources, the ability to maintain an erect posture is not necessarily degraded by a concurrent motor task. This study investigated the neural control of a particular postural-suprapostural procedure involving brain mechanisms to solve crosstalk between posture and motor subtasks. Participants completed a single posture task and a dual-task while concurrently conducting force-matching and maintaining a tilted stabilometer stance at a target angle. Stabilometer movements and event-related potentials (ERPs) were recorded. The added force-matching task increased the irregularity of postural response rather than the size of postural response prior to force-matching. In addition, the added force-matching task during stabilometer stance led to marked topographic ERP modulation, with greater P2 positivity in the frontal and sensorimotor-parietal areas of the N1-P2 transitional phase and in the sensorimotor-parietal area of the late P2 phase. The time-frequency distribution of the ERP primary principal component revealed that the dual-task condition manifested more pronounced delta (1-4 Hz) and beta (13-35 Hz) synchronizations but suppressed theta activity (4-8 Hz) before force-matching. The dual-task condition also manifested coherent fronto-parietal delta activity in the P2 period. In addition to a decrease in postural regularity, this study reveals spatio-temporal and temporal-spectral reorganizations of ERPs in the fronto-sensorimotor-parietal network due to the added suprapostural motor task. For a particular set of postural-suprapostural task, the behavior and neural data suggest a facilitatory role of autonomous postural response and central resource expansion with increasing interregional interactions for task-shift and planning the motor-suprapostural task.

Neural basis of postural focus effect on concurrent postural and motor tasks: phase-locked electroencephalogram responses.

Dual-task performance is strongly affected by the direction of attentional focus. This study investigated neural control of a postural-suprapostural procedure when postural focus strategy varied. Twelve adults concurrently conducted force-matching and maintained stabilometer stance with visual feedback on ankle movement (visual internal focus, VIF) and on stabilometer movement (visual external focus, VEF). Force-matching error, dynamics of ankle and stabilometer movements, and event-related potentials (ERPs) were registered. Postural control with VEF caused superior force-matching performance, more complex ankle movement, and stronger kinematic coupling between the ankle and stabilometer movements than postural control with VIF. The postural focus strategy also altered ERP temporal-spatial patterns. Postural control with VEF resulted in later N1 with less negativity around the bilateral fronto-central and contralateral sensorimotor areas, earlier P2 deflection with more positivity around the bilateral fronto-central and ipsilateral temporal areas, and late movement-related potential commencing in the left frontal-central area, as compared with postural control with VIF. The time-frequency distribution of the ERP principal component revealed phase-locked neural oscillations in the delta (1-4Hz), theta (4-7Hz), and beta (13-35Hz) rhythms. The delta and theta rhythms were more pronounced prior to the timing of P2 positive deflection, and beta rebound was greater after the completion of force-matching in VEF condition than VIF condition. This study is the first to reveal the neural correlation of postural focusing effect on a postural-suprapostural task. Postural control with VEF takes advantage of efficient task-switching to facilitate autonomous postural response, in agreement with the "constrained-action" hypothesis.