Table_1_How Age, Cognitive Function and Gender Affect Bimanual Force Control.DOCX

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.

双手协同控制依赖于不同半球内及半球间网络的信息处理，此类网络会因任务对称性与执行偏侧性的差异而呈现异质性。衰老、年龄相关认知损伤，以及性别因素，均可对这些网络的连接特性产生不利影响。据此，我们推测年龄、认知功能与性别会对双手力量协调产生调控作用，且此类效应会依赖于任务的核心特性（即任务难度与对称性）。本研究共纳入162名右利手被试，包括19名青年组（younger adults, YA，年龄21~30岁，其中女性9名）、52名认知健康老年组（cognitively healthy older adults, HOA，年龄80~91岁，其中女性32名）以及91名轻度认知损伤老年组（mild cognitive impairments, MCI，年龄80~91岁，其中女性37名）。所有被试均完成等长双手力量控制任务，任务要求被试追踪恒定或交替（循环正弦波）目标力，任务对称性分为五类：(i) 恒定对称任务；(ii) 不对称任务（左手维持恒定力、右手交替产生力）；(iii) 不对称任务（左手交替产生力、右手维持恒定力，即与(ii)反之亦然）；(iv) 同相交替任务；(v) 反相交替任务（双手分别以0°或180°相对相位交替运动）。本研究分析了三项核心指标：一般任务表现（靶停留时间，time on target）、双手协同性（以双手间耦合程度即线性相关系数量化）以及变异性结构（通过去趋势波动分析测得的复杂度）。分析结果显示，任务表现与双手耦合程度均显著依赖于任务对称性与执行手：在对称任务，以及左手恒定、右手交替的不对称任务中，被试的靶停留时间表现更佳。与青年组相比，认知健康老年组与轻度认知损伤老年组的靶停留时间表现更差，且在同相、反相任务中的双手耦合程度更低。此外，两组老年被试在交替力量产生任务中的变异性结构复杂度均更低，该指标可反映运动控制能力的下降。本研究还发现显著的性别效应：女性在同相、反相协同任务中的双手耦合程度更低，且在恒定力量产生任务中的变异性结构复杂度也更低。本研究结果表明，年龄与性别均对双手力量控制存在显著影响，且此类效应高度依赖于任务对称性与执行手，这可能源于半球间信息处理的不同需求。截至目前，本研究未发现双手力量控制的行为指标与年龄相关认知衰退（相较于健康衰老）之间存在明确关联，因此仍需开展进一步研究。