Reorganization of multidigit physiological tremors after repetitive contractions of a single finger

The quality of life in individuals with Parkinson's Disease: is it related to functionality and tremor severity? A cross-sectional study

BACKGROUND

Symptoms seen in Parkinson's Disease (PD) affect the quality of life (QoL) of individuals.

OBJECTIVES

This study aimed to examine the relationship of QoL with tremor severity and upper limb functionality in individuals with PD.

METHODS

Parkinson's Disease Quality of Life Questionnaire (PDQ-39) was used to examine the QoL of the participants, electromyography was used to measure the tremor amplitude, Nine-Hole Peg Test (NHPT) was used to evaluate the upper limb functionality and dynamometer was used to evaluate grip and pinch strength. Resting and postural tremor amplitudes were recorded from both sides of the hand and forearm. The relationship between QoL and other parameters was tested with Spearman Correlation Analysis. Mann-Whitney U test was used to compare individuals with and without tremor.

RESULTS

It was obtained that tremor amplitude was significantly related to: activities of daily living (rho = 0.597); emotional well-being (rho = 0.694); stigma (rho = 0.524); social support (rho = 0.595 and 0.559), and communication [rho = 0.532 (right forearm), 0.564 (left forearm), and 0.527 (right hand)] sub-parameters of PDQ-39 (p < .05). The relationship of the grip and pinch strength with the PDQ-39 sub-parameters was significant (p < .05), except for social support and communication. The relationship between NHPT and almost all parameters of PDQ-39 (p < .05), except bodily discomfort and social support, was significant.

CONCLUSION

It was concluded that future studies focusing on QoL could also consider tremor severity and grip strength as well as dexterity in individuals with PD.

The effect of standing posture on amplitude and variability of postural tremor in Parkinson’s disease

INTRODUCTION

This study examined whether altering body position (i.e., sitting or standing) affected the dynamics of physiological tremor for healthy older adults and persons with Parkinson's disease (PD). It was also of interest to determine how consistent the tremor was for both groups as determined by examining changes in within-subject variability of tremor amplitude, regularity and frequency.

METHODS

Ten Parkinsonian participants (65.1±3.2 yrs.) and twelve elderly persons (71.2±2.6 yrs.) participated in this study. Tremor was collected from the index finger and hand segments using lightweight accelerometers during the performance of a bilateral pointing task. Persons performed the pointing task in a standing or sitting position.

RESULTS

As expected, the tremor for the PD persons was greater in magnitude (mean RMS, peak power), more regular (lower SampEn), and more inconsistent from trial-to-trial (increased intra-individual variability, IIV) than the tremor recorded for the elderly. Further, when assessed during standing, the magnitude of the tremor for all individuals (elderly and PD) was greater, more variable, and less complex compared to the tremor when assessed during the sitting posture. The only measure which did not change within each group was the frequency of the major tremor peak which remained consistent, showing no significant change between limbs or as a function of the posture adopted.

CONCLUSION

The findings revealed that tremor increased in amplitude and decreased in regularity for all individuals was assessed when standing compared to sitting. It is likely that these increases were task-related, reflecting the increased physical demands of performing the task when standing rather than being driven by specific age- or disease-related changes in the mechanisms underlying tremorgenesis. Further, the tremor for the PD individuals tended to be more variable from trial-by-trial in terms of both amplitude and regularity as compared to the elderly persons. Interestingly, the only tremor metric which showed no change within each group was the frequency of the major tremor peak which was consistent within both groups irrespective of the posture adopted.

Changes in postural strategy of the lower limb under mechanical knee constraint on an unsteady stance surface

Joint constraint could limit the available degrees of freedom in a kinematic chain for maintaining postural stability. This study investigated adaptive changes in postural synergy due to bracing of bilateral knee joints, usually thought to have a trifling impact on upright stance. Twenty-four young adults were requested to maintain balance on a stabilometer plate as steadily as possible while wearing a pair of knee orthoses, either unlocked (the non-constraint (NC) condition) or locked to restrict knee motion (the knee constraint (KC) condition). Knee constraint led to a significant increase in the regularity of the stabilometer angular velocity. More than 95% of the variance properties of the joint angular velocities in the lower limb were explained by the first and second principal components (PC1 and PC2), which represented the ankle strategy and the combined knee and hip strategy, respectively. In addition to the increase trend in PC1 regularity, knee constraint enhanced the mutual information of the stabilometer angular velocity and PC1 (MI_STBV-PC1) but reduced the mutual information of the stabilometer angular velocity and PC2 (MI_STBV-PC2). The MI_STBV-PC1 was also positively correlated to stance steadiness on the stabilometer in the KC condition. In summary, in the knee constraint condition, postural synergy on the stabilometer was reorganized to increase reliance on ankle strategies to maintain equilibrium. In particular, a stable stabilometer stance under knee constraint is associated with a high level of coherent ankle–stabilometer interaction.

Adaptation of kinematic synergy and postural control to mechanical ankle constraint on an unsteady stance surface

Joint constraint interferes with the coordinative structure in joint movements used to optimize postural stability. This study aimed to investigate changes in postural synergy when the ankle joints were bilaterally braced during a stabilometer stance. Twenty-four young adults stood on a stabilometer plate while wearing a pair of ankle-foot orthoses, which were either unlocked or locked to restrict ankle motion (the ankle constraint (AC) and non-constraint (NC) conditions). Although ankle constraint did not significantly affect the dynamics of the stabilometer movements, the size and regularity of the first principal component (PC1), which explained more than 80% of the variance of joint movements in the lower limb, were increased. In addition, PC1 exhibited higher communalities with angular movements of the knee and hip joints in the AC condition than in the NC condition. Those subjects who exhibited a constraint-induced increase in postural sway (the I group) showed greater increases in the size and regularity of PC1 than did those who exhibited reduced postural sway during ankle constraint (the D group). Constraint-induced changes in postural synergy were group-dependent. Only the I group exhibited an increase of communality of PC1 with the hip angular movement following bilateral ankle constraint. In summary, bilateral ankle constraint altered the coordination solution, with increasing reliance on compensatory knee movement to maintain a balanced posture on the stabilometer. However, accessory hip movement due to ankle constraint was not economical and was disadvantageous to stance stability.

Characterization of information-based learning benefits with submovement dynamics and muscular rhythmicity

For skill advancement, motor variability must be optimized based on target information during practice sessions. This study investigated structural changes in kinematic variability by characterizing submovement dynamics and muscular oscillations after practice with visuomotor tracking under different target conditions. Thirty-six participants were randomly assigned to one of three groups (simple, complex, and random). Each group practiced tracking visual targets with trajectories of varying complexity. The velocity trajectory of tracking was decomposed into 1) a primary contraction spectrally identical to the target rate and 2) an intermittent submovement profile. The learning benefits and submovement dynamics were conditional upon experimental manipulation of the target information. Only the simple and complex groups improved their skills with practice. The size of the submovements was most greatly reduced by practice with the least target information (simple > complex > random). Submovement complexity changed in parallel with learning benefits, with the most remarkable increase in practice under a moderate amount of target information (complex > simple > random). In the simple and complex protocols, skill improvements were associated with a significant decline in alpha (8–12 Hz) muscular oscillation but a potentiation of gamma (35–50 Hz) muscular oscillation. However, the random group showed no significant change in tracking skill or submovement dynamics, except that alpha muscular oscillation was reduced. In conclusion, submovement and gamma muscular oscillation are biological markers of learning benefits. Effective learning with an appropriate amount of target information reduces the size of submovements. In accordance with the challenge point hypothesis, changes in submovement complexity in response to target information had an inverted-U function, pertaining to an abundant trajectory-tuning strategy with target exactness.

Trajectory adjustments underlying task-specific intermittent force behaviors and muscular rhythms

Force intermittency is one of the major causes of motor variability. Focusing on the dynamics of force intermittency, this study was undertaken to investigate how force trajectory is fine-tuned for static and dynamic force-tracking of a comparable physical load. Twenty-two healthy adults performed two unilateral resistance protocols (static force-tracking at 75% maximal effort and dynamic force-tracking in the range of 50%–100% maximal effort) using the left hand. The electromyographic activity and force profile of the designated hand were monitored. Gripping force was off-line decomposed into a primary movement spectrally identical to the target motion and a force intermittency profile containing numerous force pulses. The results showed that dynamic force-tracking exhibited greater intermittency amplitude and force pulse but a smaller amplitude ratio of primary movement to force intermittency than static force-tracking. Multi-scale entropy analysis revealed that force intermittency during dynamic force-tracking was more complex on a low time scale but more regular on a high time scale than that of static force-tracking. Together with task-dependent force intermittency properties, dynamic force-tracking exhibited a smaller 8–12 Hz muscular oscillation but a more potentiated muscular oscillation at 35–50 Hz than static force-tracking. In conclusion, force intermittency reflects differing trajectory controls for static and dynamic force-tracking. The target goal of dynamic tracking is achieved through trajectory adjustments that are more intricate and more frequent than those of static tracking, pertaining to differing organizations and functioning of muscular oscillations in the alpha and gamma bands.

Effects of fatigue on synergies in a hierarchical system

We investigated the effect of fatigue produced by timed maximal voluntary contraction (MVC) of the index finger of one of the hands on performance in MVC and accurate cyclic force production tasks in right-handed subjects. Based on earlier studies, we hypothesized that fatigue would produce an increase in the indices of force-stabilizing synergies in both hands as well as between the hands in two-hand tasks. Synergies were defined as co-varied adjustments of commands to fingers (modes) across cycles that stabilized total force. Fatigue caused a significant reduction in the MVC of the exercised as well as the non-exercised hand. Indices of finger enslaving (lack of individuation) increased with fatigue in both hands, although the increase was significant in the exercised hand only. In contrast to the significant effects of fatigue on MVC forces performed by the non-exercised hand, there were no comparable transfer effects on the root mean square errors during accurate force production. During one-hand tasks, both hands showed high indices of force-stabilizing synergies. These indices were larger in the left hand. Fatigue led to a general increase in synergy indices. Exercise by the left hand had stronger effects on synergy indices seen in both hands. Exercise by the right hand showed ipsilateral effects only. Smaller effects of fatigue were observed on accuracy of performance of the force-down segments of the force cycles compared to the force-up segments. For the bimanual tasks, synergies were analyzed at two hierarchical levels, two-hand (four-finger) and within-a-hand (two-finger). An increase in the synergy index with fatigue was observed at the lower (two-finger) level of the hierarchy only. We interpret the lack of effects of fatigue at the upper (two-hand) level as a consequence of a trade-off between synergies at different levels of the hierarchy. The differences between the hands are discussed within the dynamic dominance hypothesis.

Organization of physiological tremors and coordination solutions to postural pointing on an uneven stance surface

The study investigated the destabilization effect on multi-segment physiological tremors and coordinative control for a postural-suprapostural task under different stance conditions. Twenty volunteers executed postural pointing from a level surface and a seesaw balance board; meanwhile, physiological tremors of the whole postural system and fluctuation movements of fingertip/stance surface were recorded. In reference to level stance, seesaw stance led to much fewer tremor increments of the upper limb and less fluctuation movement of the fingertip than tremor increment of the lower limb and rolling movement of the stance surface. Tremor coupling between the adjacent segments organized differentially with stance surface. In reference to level stance, seesaw stance reinforced tremor coupling of the upper limb but enfeebled the coupling in the arm-lumbar and calf-foot complexes. Stance-related differences in physiological tremors could be explained by characteristic changes in the primary and secondary principal components (PC1 and PC2), with relatively high communality with segment tremors of the lower and upper limbs, respectively. Seesaw stance introduced a prominent 4-8Hz spectral peak in PC1 and potentiated 1-4Hz and 8-12Hz spectral peaks of PC2. Structural reorganization of physiological tremors with stance configuration suggests that seesaw stance involves distinct suprapostural and postural synergies for regulating degree of freedom in joint space.

Differences in cross modulation of physiological tremor in pianists and nonmusicians

PURPOSE

The study was undertaken to investigate the contralateral overflow effect on physiological tremors in pianists and nonmusicians. Group differences in cross modulation on underlying finger fractionated movement were characterized.

METHODS

Physiological tremors of the right index, middle, ring, and little fingers were recorded in 12 right-handed pianists and 12 matched nonmusician controls; meanwhile, two contralateral resistance protocols (unilateral handgrip using the left hand at slight and maximal efforts) were randomly conducted.

RESULTS

Digit tremors of the control and pianist groups were differentially modulated with the resistance protocols. An increase in gripping force led to cross excitations over 8-12 Hz digit tremors and interdigit tremor coupling for the nonmusicians. An opposite cross effect was noted for the pianists, who exhibited significant tremor suppression and the release of interdigit tremor coupling. Further analysis of tremor dynamics revealed that contralateral gripping reduced the complexity of digit tremors of the pianists but added to the tremor complexity of the nonmusicians.

CONCLUSIONS

Cross modulation on digit tremors suggests that pianists could centrally suppress unintended motor excitation across the midline. When the opposite hand is active, pianists have superior finger independence that allows them to achieve artistic aspects of musical performance.

Telemonitoring System of Neurological Signs in a Health Telematique Network

The paper presents a new, experimental, wireless tremor telemonitoring system composed of an optional variable number of portable devices integrating three-axis acceleration mini-sensors which are connected to very small dimensions acquisition systems with Wi-Fi transmission capabilities. The main advantages of the design system consist of the possibilities to monitor simultaneously many body parts of one or multiple subjects on local or more extended areas both for scheduled assessments and in an everyday life environment. Possible applications of the presented experimental system, considered as a part of a health telematic network, consist of delivering supplementary, consistent sets of data to clinicians in order to reliably assess patients’ state in home and community settings, over longer periods of time. This system consists of delivering new data necessary for differential diagnosis of different types of tremors, or to precise different stages of illness in a health telematic network. The multiple simultaneous measuring capabilities and the extended observation time period could cover eventually neglected aspects related to occasional, temporary, or an intermittent tremor. The Wi-Fi DAQ proposed system’s novelty, in contrast with existing Wi-Fi solutions, is its ultra low power Wi-Fi capability, which makes it suitable for sensing applications where battery power management is critical.