Inter-personal motor interaction is facilitated by hand pairing

The extent to which hand dominance may influence how each agent contributes to inter-personal coordination remains unknown. In the present study, right-handed human participants performed object balancing tasks either in dyadic conditions with each agent using one hand (left or right), or in bimanual conditions where each agent performed the task individually with both hands. We found that object load was shared between two hands more asymmetrically in dyadic than single-agent conditions. However, hand dominance did not influence how two hands shared the object load. In contrast, hand dominance was a major factor in modulating hand vertical movement speed. Furthermore, the magnitude of internal force produced by two hands against each other correlated with the synchrony between the two hands’ movement in dyads. This finding supports the important role of internal force in haptic communication. Importantly, both internal force and movement synchrony were affected by hand dominance of the paired participants. Overall, these results demonstrate, for the first time, that pairing of one dominant and one non-dominant hand may promote asymmetrical roles within a dyad during joint physical interactions. This appears to enable the agent using the dominant hand to actively maintain effective haptic communication and task performance.

Influence of Single-Digit Exclusions on Grip Strength in Healthy Male Adults

Grip strength (GS) of the human hand is vital to deal with objects of various sizes and shapes in daily life. The strength deteriorates if one or more digits of the hand are amputated. The main aim of this study was to determine the influence of single-digit exclusions on the GS. Healthy adults ( n = 102, male) with an age range of 20 to 70 years (mean ± SD, 31.92 ± 13.14 years) participated in the study. The movements of unused digits were restrained using splints to avoid digit enslaving effects. T (Thumb), (I) Index, M (Middle), R (Ring), L (Little) digits were chosen for exclusion based on the digit configurations. The digit configurations were IMRL, MRLT, IMRT IRLT and, IMLT with exclusions T, I, L, M, and, R respectively. The results of two-way ANOVA with repeated measures showed no significant interaction ( p = 0.923) between hand dominance and digit configurations. But statistical significance ( p = 0.000) was observed in digit configurations and hand dominance individually. The results of posthoc analysis using Bonferroni corrected pairwise comparisons showed no statistical significance ( p = 0.004) between IRLT and IMLT of both hands since the corrected p-value was 0.003. The outcomes of the F-test showed no statistical significance ( p > 0.05) between the digit configurations IMRLT, IMRL; IMRL, MRLT; MRLT, IMRT; IRLT, IMLT individually within dominant (D) and non-dominant (ND) hands. When the F-test was performed using the same digit configurations between both hands, statistical significance was not observed in all the configurations except IMLT ( p < 0.05). The results of the Pearson correlation of GS were observed to be very strong between the same digit configurations of D and ND hands.

Influence of the Inter-Trial Interval, Movement Observation, and Hand Dominance on the Previous Trial Effect

Previous studies have shown that current movement is influenced by the previous movement, which is known as the previous trial effect. In this study, we investigated the influence of the inter-trial interval, movement observation, and hand dominance on the previous trial effect of the non-target discrete movement. Right-handed healthy humans abducted the index finger in response to a start cue, and this task was repeated with constant inter-trial intervals. The absolute difference in the reaction time (RT) between the previous and current trials increased as the inter-trial interval increased. The absolute difference in RT reflects the reproducibility of the time taken for the motor execution between two consecutive trials. Thus, the finding supported the view that there is a carryover of movement information from one trial to the next, and that the underlying reproducibility of the RT between the two consecutive trials decays over time. This carryover of movement information is presumably conveyed by implicit short-term memory, which also decays within a short period of time. The correlation coefficient of the RT between the previous and current trials decreased with an increase in the inter-trial interval, indicating that the common responsiveness of two consecutive trials weakens over time. The absolute difference was smaller when the response was performed while observing finger movement, indicating that a carryover of the visual information to the next trial enhances the reproducibility of the motor execution process between consecutive trials. Hand dominance did not influence the absolute difference or correlation coefficient, indicating that the central process mediating previous trial effect of hand movement is not greatly lateralized.

State and trait of finger tapping performance in multiple sclerosis

Finger tapping tests have been shown feasible to assess motor performance in multiple sclerosis (MS) and were observed to be strongly associated with the estimated clinical severity of the disease. Therefore, tapping tests could be an adequate tool to assess disease status in MS. In this study we examined potential influencing factors on a maximum tapping task with the whole upper-limb for 10 s in 40 MS patients using linear mixed effects modelling. Patients were tested in three sessions with two trials per body-side per session over the course of 4–27 days of inpatient rehabilitation. Tested factors were the expanded disability scale (EDSS) score, laterality of MS, age, sex, hand dominance, time of day, session, trial (first or second), time between sessions, and the reported day form. A second model used these factors to examine the self-reported day form of patients. Linear mixed effects modelling indicated the tapping test to have a good inter-trial (proportional variance < 0.01) and inter-session reliability (non-significant; when controlling for time between sessions), an influence of hand-dominance (proportional variance 0.08), to be strongly associated with the EDSS (eta2 = 0.22, interaction with laterality of MS eta2 = 0.12) and to be not associated with the reported day form. The model explained 87% (p < 0.01) of variance in tapping performance. Lastly, we were able to observe a positive effect of neurologic inpatient rehabilitation on task performance obvious from a significant effect of the time between sessions (eta2 = 0.007; longer time spans between sessions were associated with higher increments in performance). Day form was only impacted by EDSS and the time of the day (p < 0.01, R2 = 0.57, eta2TIME = 0.017, eta2EDSS = 01.19). We conclude that the tapping test is a reliable and valid assessment tool for MS.

Effect of vision loss on plasticity of the head and neck proprioception

AIM: To investigate whether head and neck proprioception and motor control could be compensatory enhanced by long-term vision loss or impairment. METHODS: Individuals who were blind, low vision or sighted were included in the study, which would undergo the head repositioning test (HRT). The constant error (CE), absolute error (AE), variable error (VE) and root mean square error (RMSE) of each subject were statistically analyzed. Data were analyzed using the SAS 9.4. Tukey-Kramer for one-way ANOVA was used for comparison of blind, low vision, and sighted subjects, as well as to compare subjects with balanced vision, strong vision in the left eye and strong vision in the right eye. Independent sample t-test was used to compare subjects with congenital blindness and acquired blindness, as well as left and right hand dominance subjects. RESULTS: A total of 90 individuals (25 blind subjects, 31 low vision subjects, and 34 sighted subjects) were included in the study. Among the blind subjects, 14 cases had congenital blindness and 11 cases had acquired blindness. Among the blind and low vision subjects, 21 cases had balanced binocular vision, 17 cases had strong vision in the left eye and 18 cases had strong vision in the right eye. Among all subjects, 11 cases were left hand dominance, and 79 cases were right hand dominance. There were significant differences in AE, VE, and RMSE in head rotation between blind, low vision, and sighted subjects (P<0.01), in AE, VE, and RMSE between blind and sighted (P<0.01), and in VE and RMSE between low vision and sighted (P<0.05). No significant difference between blind and low vision (P>0.05). Significant differences in CE and AE of head right rotation and CE of general head rotation between congenital and acquired (P<0.05). No significant differences between left and right hand dominance and in balance or not of binocular vision (P>0.05). CONCLUSION: Long-term vision loss or impairment does not lead to compensatory enhancement of head and neck proprioception and motor control. Acquired experience contributes to HRT performance in the blind and has long-lasting effects on plasticity in the development of proprioception and sensorimotor control.

Get a Grip: Variation in Human Hand Grip Strength and Implications for Human Evolution

Although hand grip strength is critical to the daily lives of humans and our arboreal great ape relatives, the human hand has changed in form and function throughout our evolution due to terrestrial bipedalism, tool use, and directional asymmetry (DA) such as handedness. Here we investigate how hand form and function interact in modern humans to gain an insight into our evolutionary past. We measured grip strength in a heterogeneous, cross-sectional sample of human participants (n = 662, 17 to 83 years old) to test the potential effects of age, sex, asymmetry (hand dominance and handedness), hand shape, occupation, and practice of sports and musical instruments that involve the hand(s). We found a significant effect of sex and hand dominance on grip strength, but not of handedness, while hand shape and age had a greater influence on female grip strength. Females were significantly weaker with age, but grip strength in females with large hands was less affected than those with long hands. Frequent engagement in hand sports significantly increased grip strength in the non-dominant hand in both sexes, while only males showed a significant effect of occupation, indicating different patterns of hand dominance asymmetries and hand function. These results improve our understanding of the link between form and function in both hands and offer an insight into the evolution of human laterality and dexterity.

Carpal and cubital tunnel syndromes

Tingling, pain and numbness in the hand can be a major cause of morbidity for many people. Adequate hand and wrist function are required for a huge variety of daily tasks, therefore disorders of the hand and wrist can have significant detrimental effects on the quality of life for affected individuals. With any upper limb issue, it is important to consider hand dominance, occupation and pastimes of the affected person. This article focuses on the optimal diagnosis and management of carpal and cubital tunnel syndromes from a primary care perspective.