Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Handedness, a preference towards using the right or left hand, is established in early childhood. Such specialisation allows a higher level of skill to be maintained in the preferred hand on specific tasks through continuous practice and performance. Hand asymmetries might be expected to increase with age because of the time spent practising with the preferred hand. ⋯ Combined analyses of both hands revealed reduced asymmetries in MT and SACF in the older group. The young were significantly faster when tracing with their preferred hand, but older participants were equally slow with either hand. Our results are consistent with the growing literature reporting decreased hemispheric function lateralisation in the ageing brain.
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People with whiplash-associated disorders (WAD) not only suffer from neck/head pain, but commonly report deficits in eye movement control. Recent work has highlighted a strong relationship between eye and neck muscle activation in pain-free subjects. It is possible that WAD may disrupt the intricate coordination between eye and neck movement. ⋯ Third, the effect of horizontal gaze direction on neck muscle EMG was augmented compared to controls. These observations provide evidence of redistribution of activity between neck muscles during cervical rotation and increased interaction between eye and neck muscle activity in people with WAD. These changes in cervico-ocular coordination may underlie clinical symptoms reported by people with WAD that involve visual deficits and changes in function during cervical rotation such as postural control.
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Our previous studies of interlimb asymmetries during reaching movements have given rise to the dynamic-dominance hypothesis of motor lateralization. This hypothesis proposes that dominant arm control has become optimized for efficient intersegmental coordination, which is often associated with straight and smooth hand-paths, while non-dominant arm control has become optimized for controlling steady-state posture, which has been associated with greater final position accuracy when movements are mechanically perturbed, and often during movements made in the absence of visual feedback. The basis for this model of motor lateralization was derived from studies conducted in right-handed subjects. ⋯ While the right, non-dominant, hand-paths of left-handers were slightly more curved than those of the dominant arm, they were also substantially more accurate and better coordinated than the non-dominant arm of right-handers. Our results indicate a similar pattern, but reduced lateralization for intersegmental coordination in left-handers. These findings suggest that left-handers develop more coordinated control of their non-dominant arms than right-handers, possibly due to environmental pressure for right-handed manipulations.
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This study investigates the effects of eccentric exercise and delayed onset muscle soreness (DOMS) of the quadriceps on agonist-antagonist activity during a range of motor tasks. Ten healthy volunteers (age, mean ± SD, 24.9 ± 3.2 years) performed maximum voluntary contractions (MVC) and explosive isometric contractions of the knee extensors followed by isometric contractions at 2.5, 5, 10, 15, 20, and 30% MVC at baseline, immediately after and 24 h after eccentric exercise of the quadriceps. During each task, force of the knee extensors and surface EMG of the vasti and hamstrings muscles were recorded concurrently. ⋯ For the explosive and MVC tasks, the EMG amplitude of the vasti muscles decreased immediately after exercise and was accompanied by increased antagonist EMG for the explosive contraction only. On the contrary, reduced force steadiness was accompanied by a general increase in EMG amplitude of the vasti muscles and was accompanied by increased antagonist activity, but only at higher force levels (>15% MVC). This study shows that eccentric exercise and subsequent DOMS of the quadriceps reduce the maximal force, rate of force development and force steadiness of the knee extensors, and is accompanied by different adjustments of agonist and antagonist muscle activities.
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Field dependence/independence (FD/FI) is an important dimension of personality and cognitive styles. Different ability in mobilizing and/or allocating mental-attentional capacity was considered to be the most possible explanation for the FDI cognitive style. Many studies on characterizing the functional neuroanatomy of attentional control indicated the existence of a dissociable sub-process of conflict-monitoring and "cognitive control" system. ⋯ ERP was measured while the subjects performed the stimulus-matching tasks by categorizing two figures that were presented sequentially either as a match (same shape) or as a conflict (different shape) conditions. The results showed that the mean amplitude of N270 in FI group was higher relative to that in FD group at nearly all centrofrontal areas in the conflict condition. We conclude that the FDI cognitive styles could influence the conflict processing by the "cognitive control" system due to the different abilities of FD and FI subjects in mobilizing and/or allocating attentional resources, which can be indexed by N270.