Harmonic Passive Motion Paradigm

Humans can robustly interact with external dynamics that are not yet fully understood. This work presents a hierarchical architecture of semi-autonomous controllers that can control the redundant kinematics of the limbs during dynamic interaction, even with delays comparable to the nervous system. The postural optimisation is performed via a non-linear mapping of the system kineto-static properties, and it allows independent control of the end-effector trajectories and the arms stiffness. The proposed architecture is tested in a physical simulator in the absence of gravity, presence of gravity, and with gravity plus a viscous force field. The data indicates that the architecture can generalise the motor strategies to different environmental conditions. The experiments also verify the existence of a deterministic solution to the task-separation principle. The architecture is also compatible with Optimal Feedback Control and the Passive Motion Paradigm. The existence of a deterministic mapping implies that this task could be encoded in neural networks capable of generalisation of motion strategies to affine tasks.

Midfrontal theta tACS facilitates motor coordination in dyadic human-avatar motor interactions

Synchronous interpersonal motor interactions require moment-to-moment predictions and proactive monitoring of the partner's actions. Neurophysiologically, this is highlighted by an enhancement of midfrontal theta activity. In the present study we explored the causal role of midfrontal theta for interpersonal motor interactions employing transcranial alternating current stimulation (tACS). We implemented a realistic human-avatar interaction task in immersive virtual reality (IVR) where participants controlled a virtual arm and hand to press a button synchronously with a virtual partner. Participants completed the task while receiving theta (Experiment 1) or beta (control frequency, Experiment 2) EEG-informed tACS over the frontal midline, as well as sham stimulation as a control. Results showed that frontal theta tACS significantly improved behavioural performance (by reducing interpersonal asynchrony) and participants' motor strategies (by increasing movement times and reducing reaction times), while beta tACS had no effect on these measures. These results suggest that theta tACS over frontal areas facilitates action monitoring and motor abilities supporting interpersonal interactions.

Correlation between Motor Strategies of Balance Control and Causes of Fall in Post-Operative Elderly Individuals

BACKGROUND Falls are very much common in elderly. Fall in geriatric population is one of the common reasons for hospitalization, which may put financial burden on the patient and family. Fall in geriatric population many a times causes fracture and it may lead to serious complications which can threaten life. It may lead to disability and patient may become a handicap. In our study, we identified the correlation between motor strategies of balance control and causes of fall in post-operative elderly individuals. METHODS In this observational study, a total of 100 post-operative elderly individuals who had a fall and who underwent surgery for fracture correction were included. Both males and females in age group of 60 years and above were included. Outcome measures used were balance tests, manual muscle tests and goniometry. RESULTS 28 % individuals had fall due to low level of motor control at ankle joint and 40 % individuals at hip joint. In 16 % of individuals reaching strategy was affected. Suspensory strategy was affected in 10 % of individuals while stepping strategy was affected in 6 % of elderly. Elderly had fall due to weak musculature at hip joint (35 %), knee joint (15 %), ankle joint (30 %) and spine (25 %) irrespective of the individual’s gender. CONCLUSIONS Impairment in motor strategies of balance control such as, hip strategy, stepping strategy, reaching strategy, suspensory strategy, ankle strategy leads to fall in elderly. On the basis of assessment of manual muscle testing (MMT), range of motion and motor strategies of balance control, we concluded that impairment in motor strategies of balance, and reduced joint range of motion lead to falls. KEY WORDS Motor Strategies for Balance Control, Balance Tests, Manual Muscle Testing, Range of Motion

Arm movement adaptation to concurrent pain constraints

How do humans coordinate their movements in order to avoid pain? This paper investigates a motor task in the presence of concurrent potential pain sources: the arm must be withdrawn to avoid a slap on the hand while avoiding an elbow obstacle with an electrical noxious stimulation. The results show that our subjects learned to control the hand retraction movement in order to avoid the potential pain. Subject-specific motor strategies were used to modify the joint movement coordination to avoid hitting the obstacle with the elbow at the cost of increasing the risk of hand slap. Furthermore, they used a conservative strategy as if assuming an obstacle in 100% of the trials.

Motor Compensation Strategies for Reduced Upper Limb Function Among Individuals With Duchenne Muscular Dystrophy

The purpose of this longitudinal study was to identify and verify the compensatory motor strategies for upper limb functioning of individuals with Duchenne Muscular Dystrophy (DMD). We evaluated 32 patients diagnosed with DMD (aged 6-19 years) for cognitive and motor functioning using the Mini Mental State Examination (MMSE), Vignos Scale Jebsen Taylor Test (JTT) and Functional Skill Scale (FSS) at baseline testing and over retest intervals of six and 12 months. We used the MMSE to screen participants for capacity to engage in the research, and we analyzed absolute and percentile changes in the frequency distribution of motor strategies participants used on each JTT subtest. We also used analysis of variance with repeated measures and Bonferroni post-hoc testing of multiple comparisons to identify disease progression through FSS scores. We observed an increased frequency of compensatory motor strategies over six months. We recommend the associated use of the JTT and FSS to assess patients with DMD, since we observed worsened movement quality over a time interval of six months even while essential motor competence was maintained.

Hunting bats adjust their echolocation to receive weak prey echoes for clutter reduction

How animals extract information from their surroundings to guide motor patterns is central to their survival. Here, we use echo-recording tags to show how wild hunting bats adjust their sensory strategies to their prey and natural environment. When searching, bats maximize the chances of detecting small prey by using large sensory volumes. During prey pursuit, they trade spatial for temporal information by reducing sensory volumes while increasing update rate and redundancy of their sensory scenes. These adjustments lead to very weak prey echoes that bats protect from interference by segregating prey sensory streams from the background using a combination of fast-acting sensory and motor strategies. Counterintuitively, these weak sensory scenes allow bats to be efficient hunters close to background clutter broadening the niches available to hunt for insects.

Experience-driven remodeling of S1 digit representation in awake monkeys: the challenge of comparing active and passive touch

Many studies have compared active and passive touch to understand how motor action shapes touch perception. Current views emphasize the difficulties in making such a comparison and promote investigating how motor strategies enable the filtering out of sensory inputs to reshape touch perception. Cybulska-Klosowicz et al. (2020) suggest that primary somatosensory (S1) cortical remodeling of digit representation occurs during active touch. Here, alternative interpretations are proposed and the relevance of studying multidigit scanning is emphasized.

Ankle motor strategy use in older and younger adults as assessed by a two-dimensional kinematic analysis smart device application

Background/aims Motor strategies change with age, resulting in balance deficits. Clinical options for objectively measuring motor strategies are limited. The use of two-dimensional kinematic analysis through smart devices and applications may provide a cost-effective portable solution for measuring differences in motor strategy use between older and younger adults. The aims of this study were to investigate the concurrent validity of a two-dimensional software and two-dimensional application and to determine whether the application could capture the difference in ankle motor strategy use by older and younger adults (construct validity). Methods Video clips captured by Sony and iPad Air cameras were used to assess concurrent validity between the two-dimensional software and application. A total of 30 older (72.6 ± 4.0 years) and 30 younger (26.5±4.5 years) adults performed forward and backward stepping. A two-dimensional applicationmeasured the ankle position in degrees and time taken in seconds to initiate and complete a compensatory step. Results The two-dimensional software and app demonstrated excellent reliability (ICC2,1 ≥0.994). The ankle forward stop angle differed significantly between older and younger adults (P=0.012). No differences were observed in time taken to initiate and complete a compensatory step. Conclusions The two-dimensional application appears to be a valid alternative to two-dimensional software for measuring ankle motor strategies. Further investigation for clinical use is warranted.