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* Problem Statement: Soccer players expose themselves to repetitive head impacts (RHI) by purposefully heading the ball - an act that has been suggested to adversely affect brain structure and function and potentially contribute to the long-term development of neurodegenerative disorders. A deeper understanding of the head's kinematic response to these RHI is crucial to assess the actual risk resulting from routine soccer heading. To that aim, we investigated the influence of a comprehensive set of heading-related factors on the resulting linear and rotational acceleration of the head, as obtained by wearable sensors in a field study. * Methods: Across 26 matches, 19 semi-professional female soccer players (23.0±3.7 years) were equipped with wearable head impact sensors that registered peak linear acceleration (PLA) and peak rotational acceleration (PRA) of on-field head impact events. Actual headers were confirmed and further allocated to the following categories using video analyses: Scenario, Distance, Player Movement, Ball Reflection, Impact Location, Duel, Jump. Linear mixed models were used to assess the relationships between these factors and PLA as well as PRA. * Results: Average PLA and PRA of the head due to heading was 29.6 (±18.1) g and 6195.6 (±4448.1) rad/s², respectively. Analyses revealed a statistically significant influence of three factors on both PLA (R2=0.34) and PRA (R2=0.37). Next to subject-related factors (p<0.001; proportional variance: 12.6% [PLA] and 19.0% [PRA]), especially longer in-air distances of the ball prior to heading (p<0.001; proportional variance: 24.6% [PLA] and 19.2% [PRA]) as well as a greater extent of ball reflection due to a header (p<0.001; proportional variance: 9.2% [PLA] and 6.9% [PRA]) were significantly associated with increases in head impact kinematics. * Conclusion: Our findings demonstrate that the ball's travelling distance and the extent of ball reflection due to a header directly affect the head's kinematic response to purposeful headers in female players. Along with these factors, future studies should focus on the direct assessment of inter-individual differences in heading technique and anthropometric variables to increase the current understanding of the potential risk resulting from RHI due to soccer heading. [ABSTRACT FROM AUTHOR]

Co-activation of both hemispheres seems to play a critical role in the generation of mirror movements, involuntary muscle contractions opposite to voluntary movements of one hand. The relationship between handedness and mirror movements is unclear. We measured repetitive grip force changes performed at slow and fast frequencies with the active hand and recorded mirror activity in the opposite inactive hand in 17 healthy left-handed (LH) and 17 right-handed (RH) participants. Data suggest significant differences between RH and LH with respect to the temporo-spatial characteristics of mirror activity, but not in general mirror movement strength. Mirror activity correlation was more pronounced when the non-dominant hand was active in RH, while LH did not show such an asymmetry. We suggest that the dependence of mirror activity on the active hand in right-handers but not in left-handers reflects the more general finding of stronger manual asymmetry in brain activation as well as in functional performance in right-handers. [ABSTRACT FROM AUTHOR]

Background/objectives: Evidence regarding the effect of n-3 long-chain polyunsaturated fatty acid (LCPUFA) supplementation during pregnancy on offspring's neurodevelopment is not conclusive.Subjects/methods: In this analysis, the effect of a reduced n-6:n-3 LCPUFA ratio in the diet of pregnant/lactating women (1.2 g n-3 LCPUFA together with an arachidonic acid (AA)-balanced diet between 15th wk of gestation-4 months postpartum vs control diet) on child neurodevelopment at 4 and 5 years of age was assessed. A child development inventory (CDI) questionnaire and a hand movement test measuring mirror movements (MMs) were applied and the association with cord blood LCPUFA concentrations examined.Results: CDI questionnaire data, which categorizes children as 'normal', 'borderline' or 'delayed' in different areas of development, showed no significant evidence between study groups at 4 (n=119) and 5 years (n=130) except for the area 'letters' at 5 years of age (P=0.043). Similarly, the results did not strongly support the hypothesis that the intervention has a beneficial effect on MMs (for example, at 5 years: dominant hand, fast: adjusted mean difference, -0.08 (-0.43, 0.26); P=0.631). Children exposed to higher cord blood concentrations of docosahexaenoic acid, eicosapentaenoic acid and AA, as well as a lower ratio of n-6:n-3 fatty acids appeared to show beneficial effects on MMs, but these results were largely not statistically significant.Conclusions: Our results do not show clear benefits or harms of a change in the n-6:n-3 LCPUFA ratio during pregnancy on offspring's neurodevelopment at preschool age. Findings on cord blood LCPUFAs point to a potential influence on offspring development. [ABSTRACT FROM AUTHOR]

In this study, 26 young, 16 older adults ≤ 66a, and 22 older adults ≥ 67a were examined in a set of neuropsychological tests and the kinematics in two different activities of daily living (ADL) were assessed. Half of the participants performed the ADL in a natural speed, the other half as fast as possible. The performance in the Trail Making Task B revealed an increased slope after 67 years of age. When executed in a natural speed, ADL kinematics were comparable. When executed as fast as possible, almost all kinematic parameters showed significant group and speed differences and revealed group × speed interactions. Models of multiple linear regression predicting ADL trial durations showed similar strategies in the young and older adults < 67a. Factors were the general movement speed, the travelled path lengths, and the simultaneous use of both hands. In the older adults ≥ 67a, factors were the general movement speed, the travelled path length, and the activity level (during the task execution). A principal component analysis supported these findings by revealing two underlying components: movement strategy and age-dependent decline in primarily executive functions, where the ADL trial duration had comparable loadings on both components. These results in association with the accelerated decline in executive functions found in the oldest group suggest that deterioration of ADL with age is particularly caused by specific age-dependent changes in cognitive capacities. [ABSTRACT FROM AUTHOR]

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The influence of the cerebellum on independent finger control has rarely been investigated. We examined multidigit control in 22 patients with cerebellar degeneration, 20 patients with cerebellar stroke, and 21 patients with surgical lesions after cerebellar tumor removal. In the first task, either the index finger or the middle finger was actively lifted from an object during static holding. Both controls and cerebellar patients increased the forces of the nearby digits in synchrony with lift-off to maintain the total finger force. Patients used increased finger forces but showed no significant deficits in the pattern and timing of rearrangement of finger forces. In the second task, subjects had to press and release one finger against a force-sensitive keypad with the other fingers being inactive. All patient groups showed increased force production of the noninstructed (enslaved) fingers compared with controls. Lesionsymptom mapping in the focal patients revealed that lesions of the superior hand area were related to abnormal levels of enslaving. Increased finger forces in the finger-lifting task likely reflect an unspecific safety strategy. Increased effects of enslaving in the individuated key-press task, however, may be explained by a deterioration of cerebellar contribution to feedforward commands necessary to suppress activity in noninstructed fingers or by increased spread of the motor command intended for the instructed finger. Despite the large and diverse patient sample, surprisingly few abnormalities were observed. Both holding an object and finger typing are overlearned, automatized motor tasks, which may not or little depend on the integrity of the cerebellum. [ABSTRACT FROM AUTHOR]

High-resolution structural magnetic resonance imaging (MRI) has become a powerful tool in human cerebellar lesion studies. Structural MRI is helpful to analyse the localisation and extent of cerebellar lesions and to determine possible extracerebellar involvement. Functionally meaningful correlations between a cerebellar lesion site and behavioural data can be obtained both in subjects with degenerative as well as focal cerebellar disorders. In this review, examples are presented which demonstrate that MRI-based lesion-symptom mapping is helpful to study the function of cerebellar cortex and cerebellar nuclei. Behavioural measures were used which represent two main areas of cerebellar function, that is, motor coordination and motor learning. One example are correlations with clinical data which are in good accordance with the known functional compartmentalisation of the cerebellum in three sagittal zones: In patients with cerebellar cortical degeneration ataxia of stance and gait was correlated with atrophy of the medial (and intermediate) cerebellum, oculomotor disorders with the medial, dysarthria with the intermediate and limb ataxia with atrophy of the intermediate and lateral cerebellum. Similar findings were obtained in patients with focal lesions. In addition, in patients with acute focal lesions, a somatotopy in the superior cerebellar cortex was found which is in close relationship to animal data and functional MRI data in healthy control subjects. Finally, comparison of data in patients with acute and chronic focal lesions revealed that lesion site appears to be critical for motor recovery. Recovery after lesions to the nuclei of the cerebellum was less complete. Another example which extended knowledge about functional localisation within the cerebellum is classical conditioning of the eyeblink response, a simple form of motor learning. In healthy subjects, learning rate was related to the volume of the cortex of the posterior cerebellar lobe. In patients with focal cerebellar lesions, acquisition of eyeblink conditioning was significantly reduced in lesions including the cortex of the superior posterior lobe, but not the inferior posterior lobe. Disordered timing of conditioned eyeblink responses correlated with lesions of the anterior lobe. Findings are in good agreement with the animal literature. Different parts of the cerebellar cortex may be involved in acquisition and timing of conditioned eyeblink responses in humans. These examples demonstrate that MRI-based lesion-symptom mapping is helpful to study the contribution of functionally relevant cerebellar compartments in motor control and recovery in patients with cerebellar disease. In addition, information about the function of cerebellar cortex and nuclei can be gained. [ABSTRACT FROM AUTHOR]

Background. Although feed-forward mechanisms of grip force control are a prerequisite for skilled object manipulation, somatosensory feedback is essential to acquire, maintain, and adapt these mechanisms. Objective. Individuals with complete peripheral deafferentation provide the unique opportunity to study the function of the motor system deprived of somatosensory feedback. Methods. Two individuals (GL and IW) with complete chronic deafferentation of the trunk and limbs were tested during cyclic vertical movements of a handheld object. Such movements induce oscillating loads that are typically anticipated by parallel modulations of the grip force. Load magnitude was altered by varying either the movement frequency or object weight. Results. GL and IW employed excessive grip forces probably reflecting a compensatory mechanism. Despite this overall force increase, both deafferented participants adjusted their grip force level according to the load magnitude, indicating preserved scaling of the background grip force to physical demands. The dynamic modulation of the grip force with the load force was largely absent in GL, whereas in IW only slower movements were clearly affected. Conclusions. The authors hypothesize that the deafferented patients may have utilized visual and vestibular cues and/or an efferent copy of the motor command of the arm movement to scale the grip force level. Severely impaired grip force-load coupling in GL suggests that sensory information is important for maintaining a precise internal model of dynamic grip force control. However, comparably better performance in IW argues for the possibility that alternative cues can be used to trigger a residual internal model. [ABSTRACT FROM AUTHOR]

The grip force used to grasp and hold an object is modulated synchronously and precisely with a self-produced load indicating predictive feedforward control. It is unclear whether an externally produced load can be anticipated with similar feedforward-timing and precision if it can be predicted, e.g., because it has a periodic time course. In the present study we tested eight healthy subjects during the compensation of an externally produced sinusoidal load with cycle duration 1.5 s and more than 700 repetitions during two successive sessions. Performance parameters characterizing the timing and precision of the grip force–load coupling were analyzed across the sessions and compared with a retention measurement on the following day and with an experimental condition when the same loads were self-produced. The time lag between the grip force and the load decreased from values greater than zero to values close to zero during the practice sessions indicating a change from a more reactive to a predictive response. In contrast, the precision and economy of the coupling showed no improvement. Performance on the second day was similar to initial performance, only some retention of feedforward timing was obvious. Precision and economy of grip force control during self-produced loading was clearly superior to external loading even after extended practice. Our findings confirm that periodic external loads are controlled by predictive feedforward mechanism after sufficient experience. However, performance was not stable and did not reach the level of self-generated loading. These results are interpreted as reflecting the significance of an efferent copy of the motor command in sensorimotor processing that may be associated with a distinct neuronal representation. [ABSTRACT FROM AUTHOR]

Force control on the basis of prediction avoids time delays from sensory feedback during motor performance. Thus, self-produced loads arising from gravitational and inertial forces during object manipulation can be compensated for by simultaneous anticipatory changes in grip force. It has been suggested that internal forward models predict the consequences of our movements, so that grip force can be programmed in anticipation of movement-induced loads. The cerebellum has been proposed as the anatomical correlate of such internal models. Here, we present behavioural data from patients with cerebellar damage and data from brain imaging in healthy subjects further elucidating the role of the cerebellum in predictive force control. Patients with cerebellar damage exhibited clear deficits in the coupling between grip force and load. A positron-emission-tomography (PET) paradigm that separated the process of the grip force/load coupling from the isolated production of similar grip forces and loads was developed. Interaction and conjunction analyses revealed a strong activation peak in the ipsilateral posterior cerebellum particularly devoted to the predictive coupling between grip force and load. Both approaches clearly demonstrate that the cerebellum plays a major role in force prediction that cannot be compensated for by other sensorimotor structures in case of cerebellar disease. However, evidence suggests that also extra-cerebellar structures may significantly contribute to predictive force control: (1) grip force/load coupling may also be impaired after cerebral and peripheral sensorimotor lesions, (2) a coupling-related activation outside the cerebellum was observed in our PET study, and (3) the scaling of the grip force level and the dynamic grip force coupling are dissociable aspects of grip force control. [ABSTRACT FROM AUTHOR]

A commonly experienced effect of cold is a sensation of numbness and loss of sensibility in the fingers. Intact tactile sensibility of the grasping digits is essential for the efficient scaling of grip force level during the manipulation of hand-held objects. We investigated whether or not cooling of the grasping digits affects scaling of the grip force magnitude in relation to the loads resulting from continuous vertical arm movements performed with a grasped instrumented object. Maxima and minima of load force occurred at the lower and upper turning point of the movement cycle, respectively, and were accompanied by maximum and minimum peaks in grip force occurring close in time prior to and following digit cooling, respectively. Thus, digit cooling did not influence the ability to adjust the grip force profile in anticipation of movement-induced fluctuations in load force. However, subjects established significantly higher grip forces against the hand-held object following digit cooling and generated a 10-70% higher ratio between grip and load forces at the upper and lower turning points of the movement cycle. It is thought that the impaired economical scaling of grip force level is the result of reduced sensory feedback from the grasping fingers during digit cooling. The results provide further evidence to support the suggestion that cutaneous afferent input plays a subordinate role in the predictive temporal regulation of the grip force profile, but is used to adapt economically the force level to the actual loading requirements during dynamic object manipulation. [ABSTRACT FROM AUTHOR]

The present study examines the development of grip force modulation relating to self-induced loads during repetitive vertical arm movements at different frequencies with a hand-held object. One hundred and thirty-four 3- to 6-year-old children and 16 adults were asked to move a lightweight object up and down at increasing rates from 0.5 Hz up to individual maximal arm movement rates (>2.5 Hz). Grip forces were measured by a uni-axial force transducer and the inertial forces (tangential forces) were calculated from the measurements by accelerometers within the object. Generally, the quality of anticipatory grip force control improved from movement frequencies of 1 Hz to 2.5 Hz and decreased above 2.5 Hz. At movement frequencies below 1 Hz, the phase lag between grip and load force cycles was longer in children than in adults (children: median=17 ms; adults: median=0 ms); however, there were no significant differences between the age groups above 1.5 Hz. The grip-to-load force ratio and the grip force modulation were not significantly different from the adults up to 2.5 Hz. The fine coupling of grip and load forces (precise temporal and gain control) showed age effects among the 3- to 6-year-old children, mainly between 3- and 4-year-olds, and in adults extremely good coupling at medium arm movement frequencies. However, concerning the pure temporal coordination of grip and inertial forces, there were only differences between the 3-year-old children and the other groups at arm movement frequencies above 2.5 Hz. The results show that, during cyclic movements with hand-held loads, temporal control is well established at the age of 4 years whereas the fine gain control needs a longer time to develop. The anticipatory control is dependent on the arm movement frequency and, therefore, how rapidly the inertial loads change. The high level of anticipatory control during self-induced repetitive actions in children of 3–6 years of age is interpreted as an early developing ability to predict precisely cyclic self-induced inertial loads of hand-held objects when the object properties are known by proprioception. The timing, which is possibly related to cerebellar functions, is, to some extent, developed earlier than the gain control, which may be associated with cortical functions. [ABSTRACT FROM AUTHOR]

When we move grasped objects, our grip force precisely anticipates gravitational and inertial loads. We analysed the control of grip forces during very substantial load changes induced by parabolic flights. During these flight manoeuvres, the gravity varies between hypergravity associated with a doubling of normal terrestrial gravity and a 20-s period of microgravity. Accordingly, the contribution of the object's weight to the load changed from being twice the normal value to being absent. Two subjects continuously performed vertical and horizontal movements of an object equipped with grip force and acceleration sensors. Whereas, during vertical movements performed under normal and hypergravity, a load force maximum occurred at the lower turning point and a minimum at the upper turning point, the load force pattern was completely changed under microgravity. In particular, the upper turning point was also associated with a load force maximum. Analysis of the grip forces produced by the two subjects revealed that the grip forces underwent the same characteristic changes as the load forces. Thus, subjects were able to adjust grip forces in anticipation of arm movement-induced fluctuations in load force under different and novel load conditions. Adaptation to changing levels of gravity was also obvious when the vertical and horizontal movements were compared: grip forces depended heavily on movement direction during normal and hypergravity but not during microgravity. The predictive coupling of grip force and load force was observed even during transitions between gravity levels, indicating rapid adaptation to changing load conditions. To account for the striking preservation of the normal characteristics of grip force control, we suggest that a highly automatized, extremely flexible sensorimotor mechanism firmly implemented within the central nervous system can cope with even massive changes in the environmental conditions. [ABSTRACT FROM AUTHOR]

To determine whether the left and right hemispheres play specific roles in goal-directed movements, prehension with the ipsilesional hand was tested in patients with unilateral brain damage. The task required that subjects rotate the hand while reaching for a bar that was presented in different orientations in the frontal plane, thus making high demands on visuospatial processing. The grasped bar had to be put into a hole: under one task condition the placement of the bar was specified, while under another it was not. The constrained task required that the subject anticipate the placing action when planning the initial prehensile movement. Grip selection, reaction times, kinematics of the transport movement, and coordination of hand rotation during transport were assessed in ipsilesional movements of 22 patients with either left or right brain damage (LBD and RBD) and in control subjects. Patients in both groups exhibited performance deficits; however, impairment characteristics differed profoundly between the groups. RBD patients showed prolonged reaction time and degraded kinematics in the unconstrained task, whereas LBD patients performed relatively well when only the orientation of the bar varied, but slowly and frequently incoordinated when the subsequent action was specified. Our findings emphasize the dominant role of the right hemisphere in processing visuospatial aspects of goal-directed movements, whereas the left hemisphere subserves non-spatial aspects of preplanning under increased task demands. Correlations of the patient’s performance with results from clinical tests showed that neither deficits in visuospatial perception of RBD patients nor apraxia of LBD patients could account for the observed abnormalities in the use of the ipsilesional hand. [ABSTRACT FROM AUTHOR]

In the present study, grip forces exerted against a stationary held object were recorded during parabolic flights. Such flight maneuvers induce changes of gravity with two periods of hypergravity, associated with a doubling of normal terrestrial gravity, and a 20 s period of microgravity. Accordingly, the object’s weight changed from being twice as heavy as normally experienced and weightless. Grip-force recordings demonstrated that force control was seriously disturbed only during the first experience of hyper- and microgravity, with the grip forces being exceedingly high and yielding irregular fluctuations. Thereafter, however, grip force traces were smooth, the force level was scaled to the object’s weight under normal and high-G conditions, and the grip force changed in parallel with the weight during the transitions between hyper- and microgravity. In addition, during weightlessness, when virtually no force was necessary to stabilize the object, a low force was established, which obviously represented a reasonable safety margin for preventing possible perturbations. Thus, all relevant aspects of grip-force control observed under normal gravity conditions were preserved during gravity changes induced by parabolic flights. Hence, grip-force control mechanisms were able to cope with hyper- and microgravity, either by incorporating relevant receptor signals, such as those originating from cutaneous mechanoreceptors, or by adequately including perceived gravity signals into control programs. However, the adaptation to the uncommon gravity conditions was not complete following the first experience; finer tuning of the control system to both hyper- and microgravity continued over the measurement interval, presumably with a longer observation period being necessary before a stable performance can be reached. [ABSTRACT FROM AUTHOR]

A simple isometric motor task was used to quantify intended and unintended finger movements in two subjects (father and son) with persistent mirror movements. One hand voluntarily changed grip force between thumb and index finger at different amplitudes and frequencies, while the other hand was to maintain a constant force. During all experimental conditions the 'steady' hand showed insuppressible, highly cross-correlated contractions, compatible with bilateral distribution of a single motor command to the spinal cord. However, these associated movements were not strictly mirror images, nor did they show a fixed relationship to the voluntary movements across experimental conditions. The ratio of mirror to voluntary movement ranged from 1.4 to 19.1% and from 3.4 to 78.4% in the two subjects and was directly related to voluntary strength and speed. At maximum speed, mirror activity tended to precede voluntary activity, while it was delayed in slow force changes. Comparable time lags were not found in control subjects instructed to simulate mirror movements. We conclude that neuronal mechanisms in addition to bilateral corticomotoneuronal connections are at work in persistent mirror movements. [ABSTRACT FROM AUTHOR]

We compared matching of finger forces under isometric conditions with matching of forces produced against a spring load (anisometric conditions) in twenty normal subjects. The instruction was to generate the same force in both hands holding a grip between thumb and index finger in each hand. Visual feedback indicating the target force and the actual force applied were presented for one (reference) hand only. The forces produced in each hand were measured continuously during matching trials. A special device provided the opportunity to change from isometric to anisometric force production. Matching was required under symmetric conditions, in which force was generated in both hands either isometrically or anisometrically, as well as under asymmetric conditions in which isometric force has to be matched to anisometric force or the reverse. Under symmetric conditions matching error was consistently smaller in anisometric than in isometric force production. However, the striking feature was a severe mismatch between hands when forces had to be produced differently. For most subjects, a force generated against the spring load in the reference hand was greatly overestimated by the matching hand working isometrically. For the reverse condition consistent underestimations were observed. This effect cannot be attributed to left/right differences or a simple confusion of subjects in the asymmetric tasks. Some of the factors confounded with the conditions of force production were ruled out as an explanation by additional experimental controls. The mismatch neither depends on signals related to different finger positions associated with target forces nor is it alleviated when differently produced forces are matched sequentially. The finding that perceived muscular force depends on conditions of force production requires a reevaluation of the afferent and centrally generated signals (corollary discharge) assumed to contribute to sensations of force. [ABSTRACT FROM AUTHOR]