Direct imaging of intraflagellar-transport turnarounds reveals that motors detach, diffuse, and reattach to opposite-direction trains

Intraflagellar transport (IFT), a bidirectional intracellular transport mechanism in cilia, relies on the cooperation of kinesin-2 and IFT-dynein motors. In Caenorhabditis elegans chemosensory cilia, motors undergo rapid turnarounds to effectively work together in driving IFT. Here, we push the envelope of fluorescence imaging to obtain insight into the underlying mechanism of motor turnarounds. We developed an alternating dual-color imaging system that allows simultaneous single-molecule imaging of kinesin-II turnarounds and ensemble imaging of IFT trains. This approach allowed direct visualization of motor detachment and reattachment during turnarounds and accordingly demonstrated that the turnarounds are actually single-motor switching between opposite-direction IFT trains rather than the behaviors of motors moving independently of IFT trains. We further improved the time resolution of single-motor imaging up to 30 ms to zoom into motor turnarounds, revealing diffusion during motor turnarounds, which unveils the mechanism of motor switching trains: detach–diffuse–attach. The subsequent single-molecule analysis of turnarounds unveiled location-dependent diffusion coefficients and diffusion times for both kinesin-2 and IFT-dynein motors. From correlating the diffusion times with IFT train frequencies, we estimated that kinesins tend to attach to the next train passing in the opposite direction. IFT-dynein, however, diffuses longer and lets one or two trains pass before attaching. This might be a direct consequence of the lower diffusion coefficient of the larger IFT-dynein. Our results provide important insights into how motors can cooperate to drive intracellular transport.

The Effects of Different Types of Dual Tasking on Balance in Healthy Older Adults

Numerous of our daily activities are performed within multitask or dual task conditions. These conditions involve the interaction of perceptual and motor processes involved in postural control. Age-related changes may negatively impact cognition and balance control. Studies identifying changes related to dual-task actions in older people are need. This study aimed to determine the effects of different types of dual-tasking on the balance control of healthy older adults. The sample included 36 community-living older adults, performing two tests—a sway test and a timed up-and-go test—in three conditions: (a) single motor task; (b) dual motor task; and (c) dual motor task with cognitive demands. Cognitive processes (dual-task and cognition) affected static balance, increasing amplitude (p < 0.001) and frequency (p < 0.001) of the center of mass displacements. Dynamic balance revealed significant differences between the single motor condition and the other two conditions during gait phases (p < 0.001). The effect of dual-tasking in older adults suggests that cognitive processes are a main cause of increased variability in balance and gait when under an automatic control. During sit-to-stand, turning, and turn-to-sit movements under dual-tasking, the perceptive information becomes the most important focus of attention, while any cognitive task becomes secondary.

Pre-Bending Motion Strategy Analysis of a 3-DOF UACT Robotic Finger

Motion strategy analysis at the pre-bending stage is a fundamental component of underactuated finger grasp research. This study presents the pre-bending motion strategy and corresponding analysis of cable driving forces a 3-DOF underactuated finger comprising cable truss units. This robotic finger uses a tendon-pulley transmission and parallel four-linkage mechanism to realize the grasp capability. The structure and four motion strategies at the pre-bending stage are illustrated. The equivalent joint-driven and quasi-static motion models are established in the case where one or two cable driving forces drive the finger. In accordance with the virtual work principle, the tendon-pulley transmission is transformed into an equivalent joint-driven system. On the basis of the constraints of maximum motion space of the finger, the joint spring stiffness distributions are discussed and the finger quasi-static motion space is analyzed under the condition of single motor driving force. The unique coupled motion process and corresponding cable driving force of the finger driven by a single motor are assessed. Furthermore, three other typical quasi-static motion strategies and their corresponding cable driving forces are discussed. Valid simulation experiments are conducted to verify the accuracy of the quasi-static motion strategy. The analysis of this study can provide guidance and a theoretical reference for the design of cable-driven underactuated hands and control of the couple-driven underactuated mechanism.

Analysis of hemodynamics response in prefrontal cortex during motor and cognitive dual-task—fNIR study

Background Most of the processes occurring in the human body, need brain oxygenation. Motor and cognitive systems require neural resources and during a dual-task performance the demand on the brain increases. This study aimed to analyse the brain activation in static postural control during motor and cognitive dual-tasks. Methods Using Functional near-infrared spectroscopy (fNIR), brain activity (oxygenated hemoglobin concentration ([HbO2]), deoxygenated hemoglobin concentration ([HHb]), oxygenation difference hemoglobin concentration changes (HbOxy = HbO2 – HHb), total hemoglobin (HbTotal = HbO2 + HHb)) were measured in thirty-three young adults (age = 23.12 ± 3.86 years, mean ± SD) during three conditions: in a postural task, quiet standing (single motor task), quiet standing while performing a concurrent motor task - answer the smartphone (motor dual-task) and quiet standing while performing a concurrent cognitive task—arithmetic and memory tasks (cognitive dual-task). After data processing, the Wilcoxon signed-rank test was used for comparison. Results We found increased [HbO2] in young adults while performing cognitive dual-task compared to the single motor task and motor dual-task (P &lt; 0.05). HbOxy differences between cognitive and motor dual-task were found (P &lt; 0.05). No significant differences between single and motor dual-task in [HbO2] were observed. Conclusions Hemodynamic activity in the prefrontal cortex was significantly increased in cognitive dual-task compared to the single motor task. Pre-frontal hemodynamics appear not to be influenced by the number of motor tasks performed while the opposite occurs for the cognitive ones which may arise because the demand in the prefrontal cortex is greater in cognitive tasks while during the motor tasks the [HbO2] is recruited elsewhere.