Light touch of a stable reference reduces sway during standing. However, unexpected displacement of a light touch reference leads to short-latency reactions in ankle muscles consistent with a balance reaction, that are replaced by responses in arm muscles on subsequent trials. We anticipated that the excitability of sensorimotor pathways arising from finger cutaneous afferents would reflect these changes in behavior. We hypothesized that (1) interlimb cutaneous reflexes in muscles of the ipsilateral leg, derived from median nerve (MED) stimulation would be facilitated when touch was stable, but reduced when touch was unreliable, (2) intralimb MED reflexes in muscles of the homonymous arm would be facilitated when touch was unreliable and participants tracked the touch reference with arm movements, and (3) radial nerve (RAD) evoked reflexes would be unaffected, given that the RAD innervation territory is not involved in the light touch task. Cutaneous reflexes were evoked using a transcutaneous train of pulses (5 × 1.0 ms square-wave pulses; 300 Hz) and recorded using electromyography of muscles of the ipsilateral arm and leg. As hypothesized, interlimb MED reflexes recorded in soleus (SOL) were larger when touching the stable reference (mean ± SD % MVC; 4.78 ± 1.57) than when not touching a reference (1.00 ± 1.05) or when touching an unstable reference (1.07 ± 1.16). In addition, intralimb MED reflexes in anterior deltoid (AD) were larger when touching an unstable reference (4.50 ± 1.31), compared to touching a stable reference (1.34 ± 1.01) or not touching (1.50 ± 1.00). In contrast, interlimb RAD reflexes in SOL were larger when not touching (4.29 ± 4.34), compared with touching a stable (1.14 ± 1.84) or unstable reference (3.11 ± 4.15). These findings indicate that cutaneous reflexes from the hand are scaled with a rapid change in motor behavior when a touch reference becomes unstable, suggesting that spinal sensorimotor pathways are functionally reweighted based in part upon the reliability of tactile inputs.

轻轻触摸稳定的参考可以减少站立时的晃动。但是，轻触参考的意外位移会导致踝部肌肉的短暂反应（与平衡反应一致），随后在试验中被手臂肌肉的反应所代替。我们预期手指皮肤传入的感觉运动通路的兴奋性将反映这些行为的变化。我们假设（1）当接触稳定时，会促进由正中神经（MED）刺激引起的同侧腿部肌肉间皮的皮肤反射，但当触摸不可靠时，会减少（2）同形肌中的内臂MED反射当触摸不可靠并且参与者通过手臂移动来跟踪触摸参考时，手臂将变得容易，（3）假定RAD神经支配区域不参与轻触任务，radial神经（RAD）诱发的反射不会受到影响。使用经皮脉冲序列（5×1.0 ms方波脉冲； 300 Hz）诱发皮肤反射，并使用肌电图记录同侧手臂和腿部肌肉。如假设的那样，比起不触摸参照物（1.00±1.05）或触摸不稳定参照物（1.07±），用比目鱼（SOL）记录的比目鱼肌间反射（SOL）更大（均值±SD％MVC; 4.78±1.57）。 1.16）。此外，与接触稳定参照物（1.34±1.01）或不接触稳定参照物（1.50±1.00）相比，接触不稳定参照物（4.50±1.31）时前三角肌（AD）的下肢MED反射更大。相反，与不接触稳定（1.14±1.84）或不稳定参比（3.11±4.15）相比，未接触时SOL中的跨肢RAD反射更大（4.29±4.34）。这些发现表明，当触摸参考变得不稳定时，手部的皮肤反射会随着运动行为的快速变化而变化，这表明脊柱感觉运动通路在功能上被重新加权，部分是基于触觉输入的可靠性。