Department of Psychology, Peking University, Beijing, China 100871,
Departments of Physical Medicine and Rehabilitation, Physiology, and Applied Mathematics, Northwestern University, Chicago, Illinois 60611, Rehabilitation Institute of Chicago, Chicago, Illinois 60611, and.
J Neurosci. 2014 Sep 17;34(38):12690-700. doi: 10.1523/JNEUROSCI.1855-14.2014.
A fundamental challenge for the nervous system is to encode signals spanning many orders of magnitude with neurons of limited bandwidth. To meet this challenge, perceptual systems use gain control. However, whether the motor system uses an analogous mechanism is essentially unknown. Neuromodulators, such as serotonin, are prime candidates for gain control signals during force production. Serotonergic neurons project diffusely to motor pools, and, therefore, force production by one muscle should change the gain of others. Here we present behavioral and pharmaceutical evidence that serotonin modulates the input-output gain of motoneurons in humans. By selectively changing the efficacy of serotonin with drugs, we systematically modulated the amplitude of spinal reflexes. More importantly, force production in different limbs interacts systematically, as predicted by a spinal gain control mechanism. Psychophysics and pharmacology suggest that the motor system adopts gain control mechanisms, and serotonin is a primary driver for their implementation in force production.
神经系统面临的一个基本挑战是利用带宽有限的神经元对跨越多个数量级的信号进行编码。为了应对这一挑战，感知系统使用增益控制。然而，运动系统是否使用类似的机制基本上是未知的。神经调质，如血清素，是产生力过程中增益控制信号的主要候选者。血清素能神经元向运动池广泛投射，因此，一块肌肉的力产生应该改变其他肌肉的增益。在这里，我们提出了行为和药物学证据，表明血清素调节人类运动神经元的输入-输出增益。通过选择性地用药物改变血清素的功效，我们系统地调节了脊髓反射的幅度。更重要的是，正如脊髓增益控制机制所预测的那样，不同肢体的力产生会系统地相互作用。心理物理学和药理学表明，运动系统采用增益控制机制，而血清素是其在力产生中实现的主要驱动力。
