Dexterous Manipulation During Rhythmic Arm Movements in Mars, Moon, and Micro-Gravity

Predicting the consequences of one’s own movements can be challenging when confronted with completely novel environmental dynamics, such as microgravity in space. The absence of gravitational force disrupts internal models of the central nervous system (CNS) that have been tuned to the dynamics of a constant 1-g environment since birth. In the context of object manipulation, inadequate internal models produce prediction uncertainty evidenced by increases in the grip force (GF) safety margin that ensures a stable grip during unpredicted load perturbations. This margin decreases with practice in a novel environment. However, it is not clear how the CNS might react to a reduced, but non-zero, gravitational field, and if adaptation to reduced gravity might be beneficial for subsequent microgravity exposure. That is, we wondered if a transfer of learning can occur across various reduced-gravity environments. In this study, we investigated the kinematics and dynamics of vertical arm oscillations during parabolic flight maneuvers that simulate Mars gravity, Moon gravity, and microgravity, in that order. While the ratio of and the correlation between GF and load force (LF) evolved progressively with practice in Mars gravity, these parameters stabilized much quicker to subsequently presented Moon and microgravity conditions. These data suggest that prior short-term adaptation to one reduced-gravity field facilitates the CNS’s ability to update its internal model during exposure to other reduced gravity fields

Rasch-Built Measure of Pleasant Touch through Active Fingertip Exploration

Background: Evidence suggests that somatic sensation has a modality for pleasant touch. Objective: To investigate pleasant touch at the fingertip level (i.e., glabrous skin site) through the elaboration of a linear unidimensional scale that measures (i) various materials according to the level of pleasantness they elicit through active fingertip explorations and (ii) subjects according to their pleasantness leniency levels. Subjects: We enrolled 198 healthy subjects without any neurological disease. Methods: Blindfolded subjects actively explored 48 materials with their index fingertips and reported the perceived pleasantness of each on a 4-level scale. The fingertip moisture levels on each subject were measured before the experimental session. Data were analyzed using the Rasch model. Results: We elaborated unidimensional linear scale that included 37 materials according to their pleasantness of touch. The pleasantness level of 21 materials was perceived differently, depending on the fingertip moisture levels of the subjects. Conclusion: Based on our findings, we formulated a Pleasant Touch Scale. Fingertip moisture levels appeared to be a major factor for (un)pleasant feelings during active exploration

GRIP: Dexterous Manipulation of Objects in Weightlessness

The aim of the GRIP experiment is to investigate how gravity impacts the kinematics and dynamics of the upper limb during dexterous manipulation of objects and how the central nervous system adapts to long-term exposure to microgravity and subsequently back to Earth gravity. Hence, we proposed to conduct a set of experiments on healthy human subjects, involving the manipulation of an instrumented object during exposure to normal and microgravity, and to study how the central nervous system adapts motor control in order to cope with the new physical environment. More particularly, the coordination between the grasping force (or grip force, GF) and the load force (LF) is studied, as well as the adaptation of the movement dynamics and kinematics and the interaction between cognitive and sensory cues that establish a reference frame for the human brain. Here we describe the background motivation, the parabolic flight tests that initiated the scientific hypotheses and the technical and scientific process that led to the implementation of the GRIP experiment currently on board the International Space Station (ISS)

A novel method using EEG to characterize the cortical processes involved in active and passive touch

International audienceWe present a novel method to compare brain responses to identical tactile stimuli in active and passive touch. Using electroencephalography (EEG) to record steady-state evoked brain potentials (SS-EPs), our goal was to characterize the cortical activity related to the tactile exploration of a textured surface. For this purpose, we used a novel tactile display, which is able to produce tactile texture experiences using ultrasonic stationary waves to transiently modulate tangential friction between the finger and the display. Because the change in friction depends on the amplitude of the ultrasonic vibrations, modulation of ultrasonic vibration amplitude was used to periodically modulate friction at a frequency of 11 Hz, producing a tactile percept resembling that of a square-wave grating. After recording the exact motion of the fingertip and normal force used for each trial while one participant freely explored the surface (active touch condition), the same motion and normal force was reproduced by a high-precision robotic device with force feedback (passive touch condition). Frequency analysis of the recorded EEG signals showed that, for both active and passive touch conditions, the interactions between the fingertip and the plate elicited a robust SS-EP at 11 Hz, corresponding to the frequency of friction modulation, maximal over the parietal region contralateral to the stimulated finger. Our results suggest that the cortical activity related to active and passive touch can be characterized in humans by combining the recording of SS-EPs with an ultrasonic device generating a periodic tactile experience whose frequency is independent of finger movements

La pathogénie de l'entorse du ligament latéral externe de la cheville : évaluation d'une hypothèse

Thèse de doctorat en Kinésithérapie et réadaptation -- UCL, 198

Tactile spatial resolution measured manually: a validation study.

The purpose of this study was to investigate the validity of manual application of the grating orientation task (GOT), as currently used in fundamental and clinical research. Six examiners tested 12 subjects following recommendations of the literature. The results show that the normal force applied with the domes on the skin varied from one examiner to the next. Nevertheless, it did not affect the performance of the subjects, whose thresholds were consistent with those reported in the literature. This study highlights the inter-examiner reliability in the manual application of this test and validates this procedure

Mind Your Grip: Even Usual Dexterous Manipulation Requires High Level Cognition

Simultaneous execution of cognitive and sensorimotor tasks is critical in daily life. Here, we examined whether dexterous manipulation, a highly habitual and seemingly automatic behavior, involves high order cognitive functions. Specifically, we explored the impact of reducing available cognitive resources on the performance of a precision grip-lift task in healthy participants of three age groups (18–30, 30–60 and 60–75 years). Participants performed a motor task in isolation (M), in combination with a low-load cognitive task (M + L), and in combination with a high-load cognitive task (M + H). The motor task consisted in grasping, lifting and holding an apparatus instrumented with force sensors to monitor motor task performance. In the cognitive task, a list of letters was shown briefly before the motor task. After completing the motor task, one letter of the list was shown, and participants reported the following letter of the list. In M + L, letters in the list followed the alphabetical order. In M + H, letters were presented in random order. Performing the high-load task thus required maintaining information in working memory. Temporal and dynamic parameters of grip and lift forces were compared across conditions. During the cognitive tasks, there was a significant alteration of movement initiation and a significant increase of grip force (GF) throughout the grip-lift task. There was no interaction with “age”. Our results demonstrate that planning and the on-line control of dexterous manipulation is not an automatic behavior and, instead, that it interacts with high-level cognitive processes such as those involved in working memory

Grip Force Adjustments Reflect Prediction of Dynamic Consequences in Varying Gravitoinertial Fields

Humans have a remarkable ability to adjust the way they manipulate tools through a genuine regulation of grip force according to the task. However, rapid changes in the dynamical context may challenge this skill, as shown in many experimental approaches. Most experiments adopt perturbation paradigms that affect only one sensory modality. We hypothesize that very fast adaptation can occur if coherent information from multiple sensory modalities is provided to the central nervous system. Here, we test whether participants can switch between different and never experienced dynamical environments induced by centrifugation of the body. Seven participants lifted an object four times in a row successively in 1, 1.5, 2, 2.5, 2, 1.5, and 1 g. We continuously measured grip force, load force and the gravitoinertial acceleration that was aligned with body axis (perceived gravity). Participants adopted stereotyped grasping movements immediately upon entry in a new environment and needed only one trial to adapt grip forces to a stable performance in each new gravity environment. This result was underlined by good correlations between grip and load forces in the first trial. Participants predictively applied larger grip forces when they expected increasing gravity steps. They also decreased grip force when they expected decreasing gravity steps, but not as much as they could, indicating imperfect anticipation in that condition. The participants' performance could rather be explained by a combination of successful scaling of grip force according to gravity changes and a separate safety factor. The data suggest that in highly unfamiliar dynamic environments, grip force regulation is characterized by a combination of a successful anticipation of the experienced environmental condition, a safety factor reflecting strategic response to uncertainties about the environment and rapid feedback mechanisms to optimize performance under constant conditions

Predictive and Reactive Control of Precision Grip in Children With Congenital Hemiplegia

Background and Objectives . Grasping an object between the thumb and index finger requires precise coordination between grip force (GF) and tangential load force (LF), which is impaired in children with congenital hemiplegia (CH). This study aimed to determine the respective contributions of predictive and reactive control in the impaired precision grip of 12 children with CH between 10 and 16 years of age when compared with age- and gender-matched controls. Methods. The load of a handheld object was increased rapidly by generating an impact through the drop of a mass attached to the object. The drop was triggered by the participant (predictive conditions) or unexpectedly by the examiner (reactive conditions). In both conditions, participants aimed to prevent the object from falling. Both hands of children with CH and controls were tested. Results. During our task, no differences in the GF levels were observed between paretic, nonparetic, and control hands. Under predictive conditions, the temporal variables related to the GF were preserved before impact in children with CH but altered after impact. Under reactive conditions, the reactive delays were longer in the paretic hand. Predictive and reactive control were preserved on the nonparetic hand. Conclusions. Deficits were observed in both predictive and reactive control for the paretic hand. The predictive control exists but is altered after the impact, suggesting an inability to anticipate the consequences of a dynamic perturbation. The authors suggest that the abilities of the nonparetic side could be used in neurorehabilitation to improve motor control of the paretic side

Grip control in children before, during, and after impulsive loading.

The manipulation of small objects requires continuous contributions from both predictive and reactive mechanisms. The authors aimed to study the development of predictive and reactive mechanisms used by children from 6 to 14 years of age to manage impulsive loading. The load of a handheld object was increased rapidly by the drop of a weight hung on the object. The drop was triggered either by the child (predictive condition) or by the examiner (reactive condition). Regardless of the condition, the control strategy was refined with age. Younger children were unable to adapt their grip force (GF) to the friction of their fingers, whereas the older children provided GF that was well adapted to their variable coefficient of friction, thereby producing a secure grip. This reflected either an inadequate amount of force or an inability to integrate cutaneous information from the fingers in younger children. Additionally, a modulation with age for both predictive and reactive mechanisms was observed. All together, the better predictive abilities and the more secure grip exhibited by older children allow decreased slipping and improved performance in an impulsive loading task