School of Rehabilitation Sciences, University of Ottawa, Ottawa, Ontario K1H8M5, Canada.
Behav Brain Funct. 2010 Mar 5;6:16. doi: 10.1186/1744-9081-6-16.
Active contraction leads to facilitation of motor responses evoked by transcranial magnetic stimulation (TMS). In small hand muscles, motor facilitation is known to be also influenced by the nature of the task. Recently, we showed that corticomotor facilitation was selectively enhanced when young participants actively discriminated tactile symbols with the tip of their index or little finger. This tactile-dependent motor facilitation reflected, for the large part, attentional influences associated with performing tactile discrimination, since execution of a concomitant distraction task abolished facilitation. In the present report, we extend these observations to examine the influence of age on the ability to produce extra motor facilitation when the hand is used for sensory exploration.
Corticomotor excitability was tested in 16 healthy seniors (58-83 years) while they actively moved their right index finger over a surface under two task conditions. In the tactile discrimination (TD) condition, participants attended to the spatial location of two tactile symbols on the explored surface, while in the non discrimination (ND) condition, participants simply moved their finger over a blank surface. Changes in amplitude, in latency and in the silent period (SP) duration were measured from recordings of motor evoked potentials (MEP) in the right first dorsal interosseous muscle in response to TMS of the left motor cortex.
Healthy seniors exhibited widely varying levels of performance with the TD task, older age being associated with lower accuracy and vice-versa. Large inter-individual variations were also observed in terms of tactile-specific corticomotor facilitation. Regrouping seniors into higher (n = 6) and lower performance groups (n = 10) revealed a significant task by performance interaction. This latter interaction reflected differences between higher and lower performance groups; tactile-related facilitation being observed mainly in the former group. Latency measurements and SP durations were not affected by task conditions.
The present findings provide further insights into the factors influencing task-dependent changes in corticomotor excitability in the context of aging. Our results, in particular, highlight the importance of adjusting task demands and controlling for attention when attempting to elicit task-specific motor facilitation in older persons engaged in fine manual actions. Such information could be critical in the future for planning interventions to re-educate or maintain hand function in the presence of neurological impairments.
主动收缩会促进经颅磁刺激（TMS）诱发的运动反应。在小手部肌肉中，运动易化也受到任务性质的影响。最近，我们发现当年轻参与者用食指或小指指尖主动辨别触觉符号时，皮质运动易化会被选择性增强。这种依赖于触觉的运动易化在很大程度上反映了与执行触觉辨别相关的注意力影响，因为执行伴随的分心任务会消除易化。在本报告中，我们扩展了这些观察结果，以研究年龄对手在用于感觉探索时产生额外运动易化的能力的影响。
在两种任务条件下，测试了 16 名健康老年人（58-83 岁）的皮质运动兴奋性。在触觉辨别（TD）条件下，参与者关注被探索表面上两个触觉符号的空间位置，而在非辨别（ND）条件下，参与者只需将手指移动到空白表面。通过记录左运动皮层 TMS 对右第一背间骨间肌运动诱发电位（MEP）的幅度、潜伏期和静息期（SP）持续时间的变化来测量。
健康老年人在 TD 任务中的表现差异很大，年龄较大与准确性较低有关，反之亦然。在触觉特异性皮质运动易化方面，也观察到个体间的巨大差异。将老年人分为表现较高（n=6）和较低（n=10）的组，发现任务与表现的交互作用显著。这种后一种交互作用反映了较高和较低表现组之间的差异；在前一组中观察到与触觉相关的易化。潜伏期测量和 SP 持续时间不受任务条件的影响。
本研究结果进一步深入了解了影响衰老背景下皮质运动兴奋性与任务相关变化的因素。我们的研究结果特别强调，在精细手动操作中，当试图诱发老年人的特定任务运动易化时，需要根据任务要求进行调整，并控制注意力，这一点非常重要。这些信息在未来对于规划干预措施以重新教育或维持存在神经损伤的手部功能可能至关重要。
