Wallwork Sarah B, Talbot Kerwin, Camfferman Danny, Moseley G L, Iannetti G D
Sansom Institute for Health Research, Division of Health Sciences, University of South Australia, Adelaide, Australia; Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom.
Sansom Institute for Health Research, Division of Health Sciences, University of South Australia, Adelaide, Australia.
Cortex. 2016 Aug;81:168-75. doi: 10.1016/j.cortex.2016.04.009. Epub 2016 Apr 22.
The magnitude of the hand-blink reflex (HBR), a subcortical defensive reflex elicited by the electrical stimulation of the median nerve, is increased when the stimulated hand is close to the face ('far-near effect'). This enhancement occurs through a cortico-bulbar facilitation of the polysynaptic medullary pathways subserving the reflex. Here, in two experiments, we investigated the temporal characteristics of this facilitation, and its adjustment during voluntary movement of the stimulated hand. Given that individuals navigate in a fast changing environment, one would expect the cortico-bulbar modulation of this response to adjust rapidly, and as a function of the predicted spatial position of external threats. We observed two main results. First, the HBR modulation occurs without a temporal delay between when the hand has reached the stimulation position and when the stimulus happens (Experiments 1 and 2). Second, the voluntary movement of the hand interacts with the 'far-near effect': stimuli delivered when the hand is far from the face elicit an enhanced HBR if the hand is being moved towards the face, whereas stimuli delivered when the hand is near the face elicit an enhanced HBR regardless of the direction of the hand movement (Experiment 2). These results indicate that the top-down modulation of this subcortical defensive reflex occurs continuously, and takes into account both the current and the predicted position of potential threats with respect to the body. The continuous control of the excitability of subcortical reflex circuits ensures appropriate adjustment of defensive responses in a rapidly-changing sensory environment.
手眨眼反射（HBR）是一种由正中神经电刺激引发的皮质下防御反射，当受刺激的手靠近面部时，其反射强度会增加（“远近效应”）。这种增强是通过对介导该反射的多突触延髓通路的皮质延髓促进作用实现的。在此，我们通过两个实验研究了这种促进作用的时间特征，以及在受刺激手的自主运动过程中它是如何调整的。鉴于个体在快速变化的环境中活动，人们会预期这种反应的皮质延髓调制会迅速调整，并根据外部威胁的预测空间位置进行调整。我们观察到两个主要结果。第一，HBR调制在手部到达刺激位置与刺激发生之间不存在时间延迟（实验1和2）。第二，手部的自主运动与“远近效应”相互作用：当手远离面部时施加的刺激，如果手正朝着面部移动，则会引发增强的HBR，而当手靠近面部时施加的刺激，无论手的移动方向如何，都会引发增强的HBR（实验2）。这些结果表明，这种皮质下防御反射的自上而下调制是持续发生的，并且考虑到了潜在威胁相对于身体的当前位置和预测位置。对皮质下反射回路兴奋性的持续控制可确保在快速变化的感觉环境中对防御反应进行适当调整。
