Julius Verrel

Interacting Effects of Cognitive Load and Adult Age on the Regularity of Whole-Body Motion During Treadmill Walking

We investigated effects of concurrent cognitive task difficulty (n-back) on the regularity of whole-body movements during treadmill walking in women and men from 3 age groups (20-30, 60-70, and 70-80 years old). Using principal component analysis of individual gait patterns, we separated main (regular) from residual (irregular) components of whole-body motion. Proportion of residual variance (RV) was used as an index of gait irregularity. The gait in all age groups became more regular (reduced RV) upon introduction of a simple cognitive task (1-back), relative to walking without a concurrent cognitive task. In contrast, parametrically increasing working memory load from 1-back to 4-back led to age-differential effects, with gait patterns becoming more regular in those 20-30 years old, becoming less regular in those 70-80 years old, and showing no significant effects in those 60-70 years old. Our results support the dual-process account of sensorimotor-cognitive interactions (O. Huxhold, S.-C. Li, F. Schmiedek, and U. Lindenberger, 2006), with age-general effects of internal versus external attentional focus and age-specific effects of resource competition with increasing cognitive task difficulty.

Accuracy and Reliability of the Kinect Version 2 for Clinical Measurement of Motor Function

Background The introduction of low cost optical 3D motion tracking sensors provides new options for effective quantification of motor dysfunction. Objective The present study aimed to evaluate the Kinect V2 sensor against a gold standard motion capture system with respect to accuracy of tracked landmark movements and accuracy and repeatability of derived clinical parameters. Methods Nineteen healthy subjects were concurrently recorded with a Kinect V2 sensor and an optical motion tracking system (Vicon). Six different movement tasks were recorded with 3D full-body kinematics from both systems. Tasks included walking in different conditions, balance and adaptive postural control. After temporal and spatial alignment, agreement of movements signals was described by Pearson’s correlation coefficient and signal to noise ratios per dimension. From these movement signals, 45 clinical parameters were calculated, including ranges of motions, torso sway, movement velocities and cadence. Accuracy of parameters was described as absolute agreement, consistency agreement and limits of agreement. Intra-session reliability of 3 to 5 measurement repetitions was described as repeatability coefficient and standard error of measurement for each system. Results Accuracy of Kinect V2 landmark movements was moderate to excellent and depended on movement dimension, landmark location and performed task. Signal to noise ratio provided information about Kinect V2 landmark stability and indicated larger noise behaviour in feet and ankles. Most of the derived clinical parameters showed good to excellent absolute agreement (30 parameters showed ICC(3,1) > 0.7) and consistency (38 parameters showed r > 0.7) between both systems. Conclusion Given that this system is low-cost, portable and does not require any sensors to be attached to the body, it could provide numerous advantages when compared to established marker- or wearable sensor based system. The Kinect V2 has the potential to be used as a reliable and valid clinical measurement tool.

Normal aging reduces motor synergies in manual pointing

Depending upon its organization, movement variability may reflect poor or flexible control of a motor task. We studied adult age-related differences in the structure of postural variability in manual pointing using the uncontrolled manifold (UCM) method. Participants from 2 age groups (younger: 20-30 years; older: 70-80 years; 12 subjects per group) completed a total of 120 pointing trials to 2 different targets presented according to 3 schedules: blocked, alternating, and random. The age groups were similar with respect to basic kinematic variables, end point precision, as well as the accuracy of the biomechanical forward model of the arm. Following the uncontrolled manifold approach, goal-equivalent and nongoal-equivalent components of postural variability (goal-equivalent variability [GEV] and nongoal-equivalent variability [NGEV]) were determined for 5 time points of the movements (start, 10%, 50%, 90%, and end) and used to define a synergy index reflecting the flexibility/stability aspect of motor synergies. Toward the end of the movement, younger adults showed higher synergy indexes than older adults. Effects of target schedule were not reliable. We conclude that normal aging alters the organization of common multidegree-of-freedom movements, with older adults making less flexible use of motor abundance than younger adults.

Coordination of degrees of freedom and stabilization of task variables in a complex motor skill: expertise-related differences in cello bowing

Stringed instrument bowing is a complex sensorimotor skill, involving fine regulation of bow orientation and motion relative to the string. In this study, we characterize this skill in terms of stabilization of specific bow parameters as well as the underlying use and coordination of the degrees of freedom (DOF) of the right bowing arm. Age-matched samples of 10 advanced cellists and 10 cello novices took part in the study. Kinematic bow movement data were analyzed with respect to task variables suggested by the cello teaching literature: position and orientation of the bow relative to the string, bow velocity, and timing. Joint motion of the bowing arm was analyzed in terms of movement amplitude and inter-joint coordination (principal component analysis). As expected, novices showed poorer control of bowing parameters. In addition, novices differed markedly from advanced players in the use and coordination of the DOF of the bowing arm, with the elbow and wrist showing less overall movement and a reduced proportion of variance explained by the first principal component (PC1). In contrast, larger amounts of shoulder variance were explained by PC1 in novices compared to experts. Our findings support Bernstein’s theory of graded skill acquisition, according to which early stages of motor skill learning are characterized by a “freezing” of movement DOF, while later learning stages exploit the DOF, possibly following a proximal-to-distal sequence, for improved task performance.

Distributional properties and variance-stabilizing transformations for measures of uncontrolled manifold effects

In the uncontrolled manifold (UCM) approach, variability in elemental variables (such as joint angles or muscle modes) is decomposed into goal-equivalent and non-goal-equivalent variability components (GEV, NGEV) with regard to a specified task variable. A UCM effect is present, when GEV exceeds NGEV, and different indices have been proposed to quantify the strength of UCM effects. We propose variance-stabilizing transformations for each of these measures. Our results indicate that the variability components should be log-transformed prior to statistical analysis, to reduce non-normality and inhomogeneity of variances. Moreover, it is formally shown that the UCM indices are identical after appropriate variance-stabilizing transformations. The theoretical analysis is illustrated by empirical and simulated data from a study on manual pointing.

Repeated Structural Imaging Reveals Nonlinear Progression of Experience-Dependent Volume Changes in Human Motor Cortex

&NA; Evidence for experience‐dependent structural brain change in adult humans is accumulating. However, its time course is not well understood, as intervention studies typically consist of only 2 imaging sessions (before vs. after training). We acquired up to 18 structural magnetic resonance images over a 7‐week period while 15 right‐handed participants practiced left‐hand writing and drawing. After 4 weeks, we observed increases in gray matter of both left and right primary motor cortices relative to a control group; 3 weeks later, these differences were no longer reliable. Time‐series analyses revealed that gray matter in the primary motor cortices expanded during the first 4 weeks and then partially renormalized, in particular in the right hemisphere, despite continued practice and increasing task proficiency. Similar patterns of expansion followed by partial renormalization are also found in synaptogenesis, cortical map plasticity, and maturation, and may qualify as a general principle of structural plasticity. Research on human brain plasticity needs to encompass more than 2 measurement occasions to capture expansion and potential renormalization processes over time.

Changes in neural resting state activity in primary and higher-order motor areas induced by a short sensorimotor intervention based on the Feldenkrais method

We use functional magnetic resonance imaging to investigate short-term neural effects of a brief sensorimotor intervention adapted from the Feldenkrais method, a movement-based learning method. Twenty-one participants (10 men, 19–30 years) took part in the study. Participants were in a supine position in the scanner with extended legs while an experienced Feldenkrais practitioner used a planar board to touch and apply minimal force to different parts of the sole and toes of their left foot under two experimental conditions. In the local condition, the practitioner explored movement within foot and ankle. In the global condition, the practitioner focused on the connection and support from the foot to the rest of the body. Before (baseline) and after each intervention (post-local, post-global), we measured brain activity during intermittent pushing/releasing with the left leg and during resting state. Independent localizer tasks were used to identify regions of interest (ROI). Brain activity during left-foot pushing did not significantly differ between conditions in sensorimotor areas. Resting state activity (regional homogeneity, ReHo) increased from baseline to post-local in medial right motor cortex, and from baseline to post-global in the left supplementary/cingulate motor area. Contrasting post-global to post-local showed higher ReHo in right lateral motor cortex. ROI analyses showed significant increases in ReHo in pushing-related areas from baseline to both post-local and post-global, and this increase tended to be more pronounced post-local. The results of this exploratory study show that a short, non-intrusive sensorimotor intervention can have short-term effects on spontaneous cortical activity in functionally related brain regions. Increased resting state activity in higher-order motor areas supports the hypothesis that the global intervention engages action-related neural processes.

Older Adults Show Preserved Equilibrium but Impaired Step Length Control in Motor-Equivalent Stabilization of Gait

Stable walking depends on the coordination of multiple biomechanical degrees of freedom to ensure the dynamic maintenance of whole-body equilibrium as well as continuous forward progression. We investigated adult age-related differences in whole-body coordination underlying stabilization of center of mass (CoM) position and step pattern during locomotion. Sixteen younger (20-30 years) and 16 healthy older men (65–80 years) walked on a motorized treadmill at 80%, 100% and 120% of their self-selected preferred speed. Preferred speeds did not differ between the age groups. Motor-equivalent stabilization of step parameters (step length and width) and CoM position relative to the support (back and front foot) was examined using a generalized covariation analysis. Across age groups, covariation indices were highest for CoM position relative to the front foot, the measure most directly related to body equilibrium. Compared to younger adults, older adults showed lower covariation indices with respect to step length, extending previous findings of age-related differences in motor-equivalent coordination. In contrast, no reliable age differences were found regarding stabilization of step width or any of the CoM parameters. The observed pattern of results may reflect robust prioritization of balance over step pattern regularity, which may be adaptive in the face of age-associated sensorimotor losses and decline of coordinative capacities.

Local and global effects of neck muscle vibration during stabilization of upright standing

Neck muscle vibration (NMV) during upright standing is known to induce forward leaning, which has been explained as a global response to the (illusory) perception of a lengthening of the dorsal neck muscles. However, the effects of NMV both at the level of individual joints and on whole-body postural coordination, and its potential modulation by vision, have not yet been analyzed in detail. Eight healthy young adult participants completed a total of ten trials each, with a 10-s period of unperturbed standing followed by a 10-s period of NMV. Participants were instructed to stand “as still as possible”. This postural task was executed under two visual conditions: eyes open (EO) and eyes closed (EC). Postural responses were measured in terms of center of pressure (CoP) and center of mass (CoM) profiles, and whole-body kinematics. Responses to NMV at the level of individual body segments and joints were assessed by decomposing the time series into linear trends and residual fluctuations. Inter-segmental coordination was analyzed using a decorrelation technique, assessing motor-equivalent stabilization of four task-related variables: CoM position, trunk orientation, as well as head position and orientation. NMV induced a general forward leaning response under both visual conditions, visible in CoP, CoM, segment positions and orientations. Locally, NMV induced a pronounced extension of the atlanto-occipital joint. Residual fluctuations were higher with EC and unaffected by NMV. Coordination analysis showed that stabilization of different body parts was differentially affected by NMV. Head orientation was consistently stabilized across all conditions, with weaker coordination in the EC condition. In contrast, motor-equivalent stabilization of CoM and head position, and trunk orientation was only observed during no-vibration periods. Taken together, our results demonstrate specific effects of vision and proprioception on different aspects of local and global postural control. While perturbed neck proprioception seemed to affect the postural “set point” (inducing forward leaning), vision appeared to mainly serve in noise reduction (residual fluctuations) and control of head orientation.

Acute immobilisation facilitates premotor preparatory activity for the non-restrained hand when facing grasp affordances.

Use and non-use of body parts during goal-directed action are major forces driving reorganisation of neural processing. We investigated changes in functional brain activity resulting from acute short-term immobilisation of the dominant right hand. Informed by the concept of object affordances, we predicted that the presence or absence of a limb restraint would influence the perception of graspable objects in a laterally specific way. Twenty-three participants underwent fMRI scanning during a passive object-viewing task before the intervention as well as with and without wearing an orthosis. The right dorsal premotor cortex and the left cerebellum were more strongly activated when the handle of an object was oriented towards the left hand while the right hand was immobilised compared with a situation where the hand was not immobilised. The cluster in the premotor cortex showing an interaction between condition (with restraint, without restraint) and stimulus action side (right vs. left) overlapped with the general task vs. baseline contrast prior to the intervention, confirming its functional significance for the task. These results show that acute immobilisation of the dominant right hand leads to rapid changes of the perceived affordance of objects. We conclude that changes in action requirements lead to almost instantaneous changes in functional activation patterns, which in turn may trigger structural cortical plasticity.