Cathers I, O'Dwyer N, Neilson P
Department of Biomedical Sciences, Faculty of Health Sciences, University of Sydney, Lidcombe, NSW, Australia.
Exp Brain Res. 1996 Oct;111(3):437-46. doi: 10.1007/BF00228733.
When studying muscle stretch reflexes with tonic stimuli or making a clinical assessment of muscle tone, it is imperative that the subject does not track the stretch stimulus either consciously or unconsciously. Such tracking contaminates reflex responses with voluntary ones and so invalidates any conclusions reached. Ideally, the stimuli used should be beyond the speed of a person's tracking ability. Both experiments on tonic stretch reflexes and clinical assessment of muscle tone of necessity involve the application of perturbations to the same limb from which a response is to be measured. These perturbations produce different peripheral feedback from the limb, including particularly cutaneous signals but also different Golgi tendon and muscle spindle afference than would occur for similar movements made voluntarily. This combination of peripheral signals resulting from perturbation of a limb is referred to here as perturbational feedback. There is evidence in the literature that subjects can generate voluntary responses to same-limb perturbations within latencies normally accepted for reflexes. Such fast responses might enable faster targets to be tracked voluntarily. In this study the tracking frequency response for the forearm was investigated using sinusoidal and irregular target signals. Perturbations were applied to a manipulandum and the subjects were required to voluntarily track these perturbations under two conditions: (1) where their arm was secured in the manipulandum and therefore they had perturbational feedback of tracking errors and (2) where their tracking arm was not in contact with the manipulandum and they had only visual or kinesthetic feedback of tracking errors. For sinusoidal target inputs, perturbational feedback allowed superior tracking performance. Many subjects could produce good tracking responses at 5 Hz and some as high as 7 Hz. This is a considerably higher frequency than was found when perturbational feedback was not present and greater than has been reported in the literature for all other types of tracking (typically about 2 Hz). In contrast, when irregular signals having power up to 4 Hz were used, perturbational feedback conferred only a marginal advantage on tracking performance. The enhancement of sinusoidal tracking performance by feedback may be due to the fact that cyclic movements can be internally generated by the subject and minimal reference to external cues provided by perturbational feedback can be used to synchronise such self-generated movements with a target. In contrast, this proposed mechanism cannot be used for tracking of irregular targets. Since perturbational feedback did not improve the maximum tracking frequency for irregular targets, there was no evidence for the operation of a shorter latency, same-limb displacement response.
在使用强直性刺激研究肌肉牵张反射或对肌张力进行临床评估时，至关重要的是受试者不能有意识或无意识地追踪牵张刺激。这种追踪会使反射反应与自主反应相混淆，从而使得出的任何结论无效。理想情况下，所使用的刺激速度应超出人的追踪能力。对强直性牵张反射的实验和肌张力的临床评估都必然涉及对要测量反应的同一肢体施加扰动。这些扰动会从肢体产生不同的外周反馈，特别是包括皮肤信号，而且与自愿进行的类似运动相比，还会产生不同的高尔基腱和肌梭传入信号。因肢体扰动而产生的这种外周信号组合在这里被称为扰动反馈。文献中有证据表明，受试者能够在通常被认为是反射的潜伏期内对同一肢体的扰动产生自主反应。这种快速反应可能使受试者能够更快速地追踪目标。在本研究中，使用正弦和不规则目标信号研究了前臂的追踪频率响应。对一个操作手柄施加扰动，并要求受试者在两种条件下自主追踪这些扰动：（1）他们的手臂固定在操作手柄中，因此他们有追踪误差的扰动反馈；（2）他们的追踪手臂不与操作手柄接触，他们只有追踪误差的视觉或动觉反馈。对于正弦目标输入，扰动反馈可实现更好的追踪性能。许多受试者在5赫兹时能产生良好的追踪反应，有些受试者高达7赫兹。这一频率比不存在扰动反馈时要高得多，也高于文献中报道的所有其他类型追踪的频率（通常约为2赫兹）。相比之下，当使用功率高达4赫兹的不规则信号时，扰动反馈对追踪性能仅带来了微不足道的优势。反馈对正弦追踪性能的增强可能是由于这样一个事实，即受试者可以在内部产生循环运动，并且可以最少地参考扰动反馈提供的外部线索来使这种自我产生的运动与目标同步。相比之下，这种提出的机制不能用于追踪不规则目标。由于扰动反馈没有提高对不规则目标的最大追踪频率，因此没有证据表明存在潜伏期更短的同一肢体位移反应。
