Prehension kinematics in humans and macaques

Non-human primates, especially rhesus macaques, have been a dominant model to study sensorimotor control of the upper limbs. Indeed, human and macaques have similar hands and homologous neural circuits to mediate manual behavior. However, few studies have systematically and quantitatively compared the manual behaviors of the two species. Such comparison is critical for assessing the validity of using the macaque sensorimotor system as a model of its human counterpart. In this study, we systematically compared the prehensile behaviors of humans and rhesus macaques using an identical experimental setup. We found human and macaque prehension kinematics to be generally similar but with a few subtle differences. Humans and macaques have similar major axes of movements and similar kinematics subspaces. Human grasps are more object-specific and the movement of human digits are less correlated with each other. Monkeys demonstrate more stereotypical grasping behaviors that are common across all grasp conditions. Our results bolster the use of the macaque model to understand the neural mechanisms of manual dexterity.

Effect of Kinesio Taping on Hand Sensorimotor Control and Brain Activity

Kinesio taping has been used to improve sensorimotor control performance. In this study, we explored the effect of Kinesio taping with different tensions on hand force control, joint proprioception, reaction time and brain activity. This was an observational study with a single-group, repeated-measures design. Twenty-four healthy participants (12 women) randomly assigned to three wrist/finger flexor taping conditions: (1) taping with 20% additional tension (taping20), (2) taping with neutral tension (tapingN), and (3) without taping (control). Grip force and wrist joint proprioceptive senses, reaction time, and force control performance were recorded in each of the taping conditions. An EEG of the bilateral sensorimotor cortex and an EMG of the right finger flexors were recorded to investigate changes in brain activity and functional connectivity between the brain and muscles (coherence). Our results indicated that taping significantly improved the joint position sense for participants with an error >3° (control vs. tapingN vs. taping20: 4.1° ± 1.04° vs. 2.6° ± 0.97° vs. 2.1° ± 0.91°; p = 0.001). In addition, Kinesio taping-induced improvements in force control were moderately correlated with decreases in the EEG beta band power. In conclusion, Kinesio taping could improve the joint proprioceptive sense, and taping-induced improvement in force control is likely due to neural desynchronization in motor cortex.

The acute effects of vibratory stimuli during exercise on the sensorimotor control of the shoulder complex: A pilot study

BACKGROUND: Functional stability of the shoulder requires a balance of active forces, passive forces, and control subsystems of the joint complex. Although whole-body vibration enhances shoulder muscle function and proprioception, the impact of vibration on the sensorimotor control of the shoulder joint remains unclear. OBJECTIVE: To investigate the acute effect of vibratory stimuli on the sensorimotor control of the shoulder joint. METHODS: Fifteen male participants (age, 22.7 ± 2.3 years) were included and performed the exercise in a modified push-up position with partial weight-bearing on a vibration platform with and without vibratory stimuli. The vibration protocol included six sets lasting for 30 s each with a 30-s rest between sets. The main outcome measures included the upper limb static stability test, Upper Quarter Y Balance Test (UQYBT), and electromyography data of the upper limb. RESULTS: Vibratory stimuli resulted in an increased UQYBT score (all directions; P< 0.01) and infraspinatus, serratus anterior, and lower trapezius muscle activity (P< 0.05) between pre- and post-exercise versus the control condition. Stabilometric parameters showed no significant interaction between condition and time. CONCLUSIONS: Vibratory stimuli could maximize training benefits while limiting injury risk for athletes. Our findings could guide the development of rehabilitation programs for patients with shoulder instability.

Force variability is mostly not motor noise: Theoretical implications for motor control

Variability in muscle force is a hallmark of healthy and pathological human behavior. Predominant theories of sensorimotor control assume ‘motor noise’ leads to force variability and its ‘signal dependence’ (variability in muscle force whose amplitude increases with intensity of neural drive). Here, we demonstrate that the two proposed mechanisms for motor noise (i.e. the stochastic nature of motor unit discharge and unfused tetanic contraction) cannot account for the majority of force variability nor for its signal dependence. We do so by considering three previously underappreciated but physiologically important features of a population of motor units: 1) fusion of motor unit twitches, 2) coupling among motoneuron discharge rate, cross-bridge dynamics, and muscle mechanics, and 3) a series-elastic element to account for the aponeurosis and tendon. These results argue strongly against the idea that force variability and the resulting kinematic variability are generated primarily by ‘motor noise.’ Rather, they underscore the importance of variability arising from properties of control strategies embodied through distributed sensorimotor systems. As such, our study provides a critical path toward developing theories and models of sensorimotor control that provide a physiologically valid and clinically useful understanding of healthy and pathologic force variability.