Journal of Motor Behavior最新文献

Light touch contact of the fingertip reduces postural sway. The light touch effect was confirmed in several postural orientations. However, the effect on postural control in the crouching posture remains unclear. This study investigated the effect of a light fingertip touch on the perturbation of the center of pressure in bipedal standing and crouching. Twenty-two healthy participants engaged in eight postural control tasks: standing/crouching (Posture) × eyes opened/eyes closed (Vision) × light touch/no touch (Touch). The total trajectory length and root-mean-square of the center of pressure in the anterior-posterior and medio-lateral directions were analyzed. Light touch reduced the sway of the center of pressure in both the standing and crouching postures, particularly in the anterior-posterior direction. Furthermore, the touch effect on the sway of the center of pressure varied between the standing and crouching postures. Consistent effects were observed in the anterior-posterior direction, but differing effects were observed in the medio-lateral direction. These results indicate that somatosensory input from the fingertip reduces postural sway in both directions in a crouched posture. Variations of the center of pressure disturbances in the medio-lateral direction could originate from differences in postural strategies involving the ankle and hip joints between bipedal standing and crouching positions.

Cutaneous feedback plays a large role in the reflexive activation of muscle activity (Ia stretch reflex) generating postural responses during planned gait termination. As the mechanisms to induce a cutaneous afferent volley have been limited to electrical stimulation, it remains unknown if mechanical stimuli can modulate stretch reflex (SR) excitability. The purpose of this study was to examine the effect of adding cutaneous inputs on modulating the SR during perturbed gait termination. Thirty young adults completed walking trials when a platform unexpectedly tilted 10 degrees anteriorly or posteriorly, inducing a tibialis anterior (TA) or medial gastrocnemius (MG) short-latency reflex. The SR latency, the peak SR amplitude, and the total SR amplitude of the agonist burst, were compared between the stretched muscle and cutaneous facilitation. Statistically significant interactions were observed between the stretched muscle and cutaneous facilitation on the SR peak and SR burst. More notably, texture resulted in a consistent expression on the TA SR magnitude, without a similar effect in MG. Despite confirming the ability of cutaneous afferent facilitation on modulating spinal interneuronal circuitry, participant variability in response to texture highlights the importance of focusing on individual participant results when studying the effects of cutaneous facilitation on modulating spinal motorneuron excitability.

Standing at elevated heights can elicit postural adjustments often characterized by reduced center of pressure (COP) magnitude, higher frequencies, and increased irregularity. While often attributed to postural stiffening, such changes may also reflect a shift toward more automatic control. However, most height-related studies use a feet-parallel stance, which may not be generalized to more constrained foot positions like semi-tandem, which are often encountered in real-world height situations. This study investigated the effects of acute virtual height exposure on postural control in a semi-tandem stance. Twenty young adults stood on a force platform under three conditions: (1) no VR, (2) VR sidewalk at ground level, and (3) VR elevated plank. Each participant completed six 60-second trials per condition. Repeated-measures ANOVAs revealed that wearing the VR headset alone affected postural control, with further changes under height exposure. Height was associated with increased COP frequency and irregularity, suggesting more automatic control. However, due to biomechanical constraints, the semi-tandem stance may have influenced postural strategies, resulting in increased COP variability. These findings support the use of VR to study postural threat and highlight the role of foot position in postural adaptations.

Gait stability and walking direction control are conventionally attributed to coordination among somatosensory, visual, and vestibular systems. Recent evidence of functional interdependence between masticatory and neuromuscular systems indicates that the stomatognathic system is neurologically integrated with various body systems relevant to movement planning and execution. This study investigated the effects of unilateral molar biting and incisor biting on walking with and without visual feedback. A cohort of 31 healthy young adults aged 21 to 30 years (average age of 23.93 ± 1.89) participated in this study. Three types of errors in walking direction (angle error, position error, and curve error) were computed. Our findings indicate that, in right-handed individuals, irrespective of visual feedback, unilateral biting caused systematic deviations toward the biting side from initiation to termination of walking. The consistent deviation in walking, particularly during unilateral right biting conditions in right-handed individuals, may indicate a complex interplay between masticatory function and gait control mechanism, potentially influenced by handedness and motor lateralization within the cortex. This study establishes a foundation for future research exploring the interrelation between bite location, visual feedback, and motor control in diverse populations. This research may provide insight for more efficient interventions for gait-related disorders.

Individuals post-stroke commonly demonstrate alterations in motor behavior with regard to both task performance and the motor strategies used in pursuit of task goals. We evaluated whether constraining postural sway (motor strategy) during practice would affect upper-limb precision aiming performance (task performance) and postural control adaptations. Adults with stroke stood on a force plate while immersed in a virtual scene displaying an anterior target. Participants aimed to position a virtual laser pointer (via handheld device) in the target. Participants then completed practice trials involving aiming at a lateral target. For this practice session, participants were randomized to either (a) a "constraint" group wherein they received physical constraint to limit postural sway, or (b) a "no-constraint" group. Task performance and postural control were assessed before and after practice, and transfer to another upper-limb task was evaluated. After practice, both groups improved paretic upper-limb performance. For the target task, the no-constraint group showed task-sensitive changes in postural control. The constraint group showed no changes in postural control. At transfer, the constraint group increased postural sway. Constraining postural sway after stroke should be carefully considered with the recognition that postural sway arises from exploratory movements involved in the discovery of adaptable motor solutions.

Walking turns require coordinated axial segment rotations combined with step placement modifications. Visual information can inform this coordination and is used in three stages of processing: to identify the stimulus, select the appropriate response, and execute the response. We adapted a Simon task protocol to explore how response selection impacts walking turn execution. Young adults (n = 24; 15 female; 24.9 ± 4.5 years) completed walking turns to goals located 60 degrees left or right of their walking path. In some trials, heel contact with a force plate triggered appearance of an arrow on the same side (congruent), opposite side (incongruent) or in the middle (neutral) of a screen. To determine impact of different biomechanical demands for task execution, researchers specified which foot to initiate gait for each trial; this ensured visual cues were triggered either by the same limb as the turn direction (ipsilateral) or opposite (contralateral). We observed that head and trunk yaw motion was initiated earlier and with greater relative rotation magnitude for incongruent visual cues. Step width adaptations were also observed for both step patterns when responding to incongruent visual cues. Conflict at the response selection phase of visual processing disrupts typical turning behaviors of young adults.

Optokinetic stimulation (OKS) induces visual-vestibular conflict, influencing postural stability. Virtual reality (VR)-based OKS provides an immersive alternative to conventional screen-based OKS, potentially enhancing vestibular rehabilitation. This study investigated the effects of VR-based OKS on head and trunk instability while standing on a continuous sinusoidal moving platform. Sixteen healthy adult males participated. Six experimental conditions combined three visual conditions (eyes open, eyes closed, VR-based OKS) with two platform frequencies (0.5 Hz, 1.0 Hz). Head and trunk accelerations were recorded using inertial measurement units, and root mean square values were analyzed. Cross-correlation between head and trunk sway was assessed. VR-based OKS induced significantly greater lateral trunk sway compared to the eyes-open condition (p = 0.003). Cross-correlation analysis showed a significant association between lateral head and trunk sway under OKS, with a moderate correlation at 0.5 Hz (r = 0.540, p < 0.05) and a strong correlation at 1.0 Hz (r = 0.793, p < 0.01). VR-based OKS dynamically alters sensory reweighting, inducing synchronized head-trunk movements. These findings highlight the potential use of VR-based OKS in vestibular rehabilitation and underscore the importance of adjusting stimulus intensity to suit individual needs. Further research should explore long-term adaptation effects.

Age-related manual dexterity impairments may critically depend on cognitive impairments. This study examined associations between task demands, cognitive function and dexterity impairments in older adults. A total of 42 participants, 21 young (age 19-39; 12 female, 9 male) and 21 older (age 65-88; 12 female and 9 males) adults performed the Grooved Pegboard test under single-task, dual task (visuospatial and nonspatial tasks) and bilateral (finger-tapping test) conditions. Cognitive and executive function were assessed with the Montreal Cognitive Assessment (MoCA) and Trail Making Test (TMT). Older adults showed uniform declines in Grooved Pegboard performance across secondary tasks compared to young adults. Older adults with cognitive deficits (MoCA < 26) took 34% longer to complete the Grooved Pegboard during the nonspatial task compared to healthy older adults. The bilateral task revealed Grooved Pegboard and finger tapping impairments in older adults, particularly those with cognitive deficits, relative to young adults. Significant correlations between increased TMT B completion time and decreased Grooved Pegboard (r = 0.732) and finger-tapping (r = -0.663) performance highlights a relationship between executive function and dexterity impairments in older adults with cognitive deficits. Results suggest the role of cognitive impairments in motor function and the use of task-specific motor assessments.

The Timed Up-and-Go (TUG) test, a clinical assessment tool of functional mobility and balance scale for fall risk, is potentially helpful for evaluating anticipatory locomotor adjustments (ALA). This study aimed to simplify ALA evaluation in older adults using the TUG test. Thirty-eight older adults (mean ± SD: 74.97 ± 6.42 years) and 24 younger adults (25.16 ± 4.82 years) participated. Two identical poles replaced the cone-shaped object, creating the "obstacle TUG (Obs-TUG) test." Participants chose between passing between the poles or detouring around them. We examined the quality of ALA in terms of their route selection. Results showed that older adults selected a detour more frequently than younger adults, even if the opening between the two poles was so wide that passing through the opening required less time than taking a detour. Older adults were characterized by shorter step lengths and narrower step widths while turning, indicating prioritization of stability over efficiency. The Obs-TUG test effectively describes ALA characteristics in older adults through consistent behavioral choices in route selection and walking patterns.

This study investigated the effects of Adapted Tango (AT) on dynamic balance, dual-tasking, and leg muscle antagonist activity in individuals with Parkinson's disease (PD), a condition characterized by cognitive and muscular difficulties. A total of 33 participants with mild-to-moderate PD were recruited and assigned to either an AT group (n = 16, 9 M/7F) or a control group (n = 17, 10 M/7F). Participants' dual-task performance was evaluated using Serial 7 walking tasks and the Dynamic Gait Index (DGI) at three different time points: before the intervention, immediately after, and four weeks post-intervention. Additionally, muscle activity modulation (the ability to activate and inhibit muscles appropriately) was quantified using Modulation Indices (MI) derived from EMG data. The results demonstrated an improvement in dual-task performance following the AT intervention; however, these differences between the AT and control groups were not statistically significant (p > 0.05). Notably, significant enhancements in DGI scores were observed in the AT group compared to controls (p < 0.05). Conversely, MI did not significantly change after the intervention (p > 0.05). This research highlights the potential of Adapted Tango in enhancing dynamic balance for individuals with PD, suggesting a need for larger-scale randomized trials to provide further evidence and inform clinical practice.