Abstract
Coordinated bimanual control depends on information processing in different intra- and interhemispheric networks that differ with respect to task symmetry and laterality of execution. Aging and age-related cognitive impairments, but also sex can have detrimental effects on connectivity of these networks. We therefore expected effects of age, cognitive function and sex on bimanual force coordination. We furthermore expected these effects to depend on the characteristics of the task (i.e., difficulty and symmetry). 162 right handed participants (19 younger adults [YA], 21–30 years, 9 females; 52 cognitively healthy older adults [HOA], 80–91 years, 32 females; and 91 older adults with mild cognitive impairments [MCI] 80–91 years, 37 females) performed isometric bimanual force control tasks that required following constant or alternating (cyclic sine-wave) targets and varied in symmetry, i.e., (i) constant symmetric, asymmetric [with constant left and alternating right (ii) or vice versa (iii)], (iv) alternating in- and (v) alternating antiphase (both hands alternating with 0° or 180° relative phase, respectively). We analyzed general performance (time on target), bimanual coordination as coupling between hands (linear correlation coefficient) and structure of variability (i.e., complexity measured through detrended fluctuation analysis). Performance and coupling strongly depended on task symmetry and executing hand, with better performance in symmetric tasks and in asymmetric tasks when the left hand produced a constant and the right hand an alternating force. HOA and MCI, compared to YA, showed poorer performance (time on target) and reduced coupling in in- and antiphase tasks. Furthermore, both groups of OA displayed less complex structure in alternating force production tasks, a marker of reduced control. In addition, we found strong sex effects with females displaying reduced coupling during in- and antiphase coordination and less complex variably structure in constant force production. Results of this study revealed strong effects of age, but also sex on bimanual force control. Effects depended strongly on task symmetry and executing hand, possibly due to different requirements in interhemispheric information processing. So far, we found no clear relationship between behavioral markers of bimanual force control and age-related cognitive decline (compared to healthy aging), making further investigation necessary.
Highlights
Many daily bimanual tasks require precise force adjustments for object stabilization and manipulation, e.g., when buttoning shirts or tying laces
Absolute force values of the younger adults (YA) participants were larger than both older adults (OA) and mild cognitive impairments (MCI), resulting from differences in maximum voluntary contraction (MVC)
All three individuals display better constant force performance during the both constant condition than during the asymmetric condition. This was true in healthy OA (HOA) and MCI as compared to YA
Summary
Many daily bimanual tasks require precise force adjustments for object stabilization and manipulation, e.g., when buttoning shirts or tying laces. Fine motor skills are an important factor for independent living. They are, often compromised in late adulthood (Vieluf et al, 2013). Bimanual task demands can add a further challenge to fine motor control, as they require precise spatiotemporal coordination of both hands. Different task-dependent intra- and interhemispheric neural networks [e.g., involving the primary motor cortex (M1), supplementary motor area (SMA), and premotor cortex (PMC), the cingulate and posterior parietal cortex; Swinnen, 2002] are necessary for controlling bimanual movement tasks. Connection between the two hemispheres is primarily established via the corpus callosum (CC) (Gooijers and Swinnen, 2014)
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