Cerebral dominance and spinal excitability in cognition of motor space

我们之前已经证明，当头部旋转方向与定位运动相同时，手臂和手指的定位是下凸的，而当头部旋转方向与定位运动相反时，手臂和手指的定位是上凸的。这种偏倚效应被认为是由于头部旋转引起的反射效应或空间感知和控制手臂和手指位置的认知扭曲引起的。在本研究项目中，我们研究了手臂和手指定位在90°头部旋转时的反应偏倚效应的两个可能来源。(1)采用CNV范式进行了反应时间实验，以检验大脑优势对将注意力导向对侧半脑内的反应时间刺激的影响。结果显示，C3和C4的CNVs振幅都很小，没有侧边效应。这表明在本实验中使用的简单反应时间任务中，受试者可能没有将注意力定向到对侧半球。我们将在未来的项目中进一步研究受试者的注意力方面，使用选择反应时间任务来操纵受试者的注意力向对侧半球转移。(2)在头部旋转完成后的14秒内检查比目鱼h反射。在完成头部旋转后，比目鱼h反射的振幅增加到控制h反射（静止时）的150%左右。然后在6或7秒内逐渐恢复到控制水平。因此，头部旋转对脊髓运动神经元兴奋性的影响不会超过头部旋转后约6或7秒。这意味着由于头部旋转引起的脊柱反射效应被排除为手臂和手指定位时出现的反应偏倚效应的来源。

We previously demonstrated that arm and finger positioning was undershot when the head was rotated in the same direction as the positioning movement and overshot when the head was rotated in the direction opposite to positioning movement. Such biasing effects were assumed to arise etiher from some reflex effects due to head rotation or cognitive distortion in spatial pereception and control of arm and finger positioning. We examined in this research project two likely sources of the response biasing effects in arm and finger positioning with 90ﾟ head rotation. (1) A reaction-time experiment with a CNV paradigm was conducted to test the effects of cerebral dominance for directing attention towards reaction time stimuli that were given within the contralateral hemispace. Result showed only small amplitudes in CNVs at both C3 and C4, with the absence of laterality effects. This indicates the subjects may not have directed their attention to contralateral hemispace in the simple reaction time task used in this experiment. We will further examine in the future project the aspext of subjects' attention, using a choice reaction time task to manipulate subiject's attention toward contralateral hemispace. (2) The soleus H-reflex was examined throgh the period of 14 seconds after completion of head rotation. The amplitude of soleus H-reflex increased up to about 150% of controlH-reflex (at rest) just after the completion of head rotation. This then gradually returned to control level with in 6 or 7 sec. The head rotation could therefore affect spinal motoneuronal excitability no longer than about 6 or 7 sec after head rotation. This implies that the spinal reflex effect due to head rotation is ruled out as a sourceof the response biasing effect appearing in arm and finger positioning with 90ﾟ head-rotation.