Functional imaging studies have shown that seniors exhibit more elaborate brain activation than younger controls while performing motor tasks. Here, we investigated whether this age-related overactivation reflects compensation or dedifferentiation mechanisms. "Compensation" refers to additional activation that counteracts age-related decline of brain function and supports successful performance, whereas "dedifferentiation" reflects age-related difficulties in recruiting specialized neural mechanisms and is not relevant to task performance. To test these predictions, performance on a complex interlimb coordination task was correlated with brain activation. Findings revealed that coordination resulted in activation of classical motor coordination regions, but also higher-level sensorimotor regions, and frontal regions in the elderly. Interestingly, a positive correlation between activation level in these latter regions and motor performance was observed in the elderly. This performance enhancing additional recruitment is consistent with the compensation hypothesis and characterizes neuroplasticity at the systems level in the aging brain.
Although functional imaging studies have frequently examined age-related changes in neural recruitment during cognitive tasks, much less is known about such changes during motor performance. In the present study, we used functional magnetic resonance imaging to investigate age-related changes in cyclical hand and/or foot movements across different degrees of complexity. Right-handed volunteers (11 young, 10 old) were scanned while performing isolated flexion-extension movements of the right wrist and foot as well as their coordination, according to the "easy" isodirectional and "difficult" nonisodirectional mode. Findings revealed activation of a typical motor network in both age groups, but several additional brain areas were involved in the elderly. Regardless of the performed motor task, the elderly exhibited additional activation in areas involved in sensory processing and integration, such as contralateral anterior insula, frontal operculum, superior temporal gyrus, supramarginal gyrus, secondary somatosensory area, and ipsilateral precuneus. Age-related activation differences during coordination of both segments were additionally observed in areas reflecting increased cognitive monitoring of motor performance, such as the pre-supplementary motor area, pre-dorsal premotor area, rostral cingulate, and prefrontal cortex. In the most complex coordination task, the elderly exhibited additional activation in anterior rostral cingulate and dorsolateral prefrontal cortex, known to be involved in suppression of prepotent response tendencies and inhibitory cognitive control. Overall, these findings are indicative of an age-related shift along the continuum from automatic to more controlled processing of movement. This increased cognitive monitoring of movement refers to enhanced attentional deployment, more pronounced processing of sensory information, and intersensory integration.
This study explores the associations between polymorphisms in two candidate genes-myostatin gene (MSTN or GDF8) and angiotensin-converting enzyme (ACE) gene-with interindividual differences in human muscle mass and strength responses to strength training. The MSTN AluI A55T (exon 1), BanII K153R, TaqI E164 K and BstNI P198A (all in exon 2) markers and the ACE insertion (I)/deletion (D) polymorphism were typed in 57 males [22.4 (3.7) years] who participated in a 10-week, high-resistance training program for the elbow flexors. Maximal strength, and maximal isometric and concentric elbow flexor torques were measured at baseline and after training. Information on muscle cross-sectional area of the upper arm was obtained by computer tomography scans. Only one individual was heterozygous for the MSTN BanII K153R variant. No allelic variant was detected at the other MSTN sites in this population. For the ACE I/D polymorphism, no evidence was found for an association of the D or I allele with baseline strength, isometric and concentric torque or arm muscle cross-sectional area [analysis of covariance (ANCOVA) 0.25< P<0.97]. Responses to the strength-training program were not associated with the ACE I/D genotype (ANCOVA 0.057< P<0.70). Borderline significance was found for larger strength gains in dynamic flexion torques for I/I genotypes. This study therefore does not support the hypothesis that an increased muscle fiber hypertrophic effect of strength training is present in D-allele carriers.
Age-related differences in regional brain activation during two different movement generation modes were examined. Old and young volunteers were scanned while performing cyclical hand-foot flexion-extension movements in the presence and the absence of augmented visual feedback, referring to external and internal movements generation, respectively. Performing the coordination task under both conditions resulted in the activation of two distinct neural networks in the young adults, i.e., the hMT/V5+, and parietal and premotor cortices were typically involved during the visually guided mode, whereas the supplementary motor area (SMA), cingulate motor area (CMA), frontal operculum (FO) and secondary somatosensory area (S2) were typically involved during internally guided movements. Remarkably, much less differentiation between both feedback dependent networks was observed in the seniors, i.e., they exhibited high activity in the SMA, CMA, FO and S2 during both modes, suggesting that the typical network differentiation was largely diminished. This is hypothesized to reflect a general increase in processing resources within areas contributing to motor control and associated sensory processing, supporting motor performance in the elderly.
Young and elderly participants performed concurrent ipsilateral hand-foot movements either isodirectionally or nonisodirectionally. We determined performance by measuring the maximal cycling frequency at which the coordination pattern could be performed successfully (CF(max)). We also determined attentional costs by means of a dual-task paradigm. Findings revealed that CF(max) was significantly lower in the elderly than in the young participants for the nonisodirectional mode, whereas we observed no differences for the isodirectional mode. Under dual-task conditions, coordination deteriorated in the elderly group only. However, when we equated levels of task difficulty, differences between the groups disappeared. Furthermore, attentional costs did not differ between isodirectional and nonisodirectional movements. This indicates that age-related coordination deficits were not primarily evoked by reduced attentional resources or control in elderly persons.
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