Dixon Luke, Ibrahim Mohamed M, Santora Danielle, Knikou Maria
Department of Physical Therapy, College of Staten Island, New York, New York.
Graduate Center, City University of New York, New York, New York; and Department of Physical Therapy, College of Staten Island, New York, New York
J Neurophysiol. 2016 Aug 1;116(2):904-16. doi: 10.1152/jn.00259.2016. Epub 2016 Jun 8.
Anatomical, physiological, and functional connectivity exists between the neurons of the primary motor cortex (M1) and spinal cord. Paired associative stimulation (PAS) produces enduring changes in M1, based on the Hebbian principle of associative plasticity. The present study aimed to establish neurophysiological changes in human cortical and spinal neuronal circuits by pairing noninvasive transspinal stimulation with transcortical stimulation via transcranial magnetic stimulation (TMS). We delivered paired transspinal and transcortical stimulation for 40 min at precise interstimulus intervals, with TMS being delivered after (transspinal-transcortical PAS) or before (transcortical-transspinal PAS) transspinal stimulation. Transspinal-transcortical PAS markedly decreased intracortical inhibition, increased intracortical facilitation and M1 excitability with concomitant decreases of motor threshold, and reduced the soleus Hoffmann's reflex (H-reflex) low frequency-mediated homosynaptic depression. Transcortical-transspinal PAS did not affect intracortical circuits, decreased M1 excitability, and reduced the soleus H-reflex-paired stimulation pulses' mediated postactivation depression. Both protocols affected the excitation threshold of group Ia afferents and motor axons. These findings clearly indicate that the pairing of transspinal with transcortical stimulation produces cortical and spinal excitability changes based on the timing interval and functional network interactions between the two associated inputs. This new PAS paradigm may constitute a significant neuromodulation method with physiological impact, because it can be used to alter concomitantly excitability of intracortical circuits, corticospinal neurons, and spinal inhibition in humans.
初级运动皮层（M1）的神经元与脊髓之间存在解剖学、生理学和功能上的连接。基于联合可塑性的赫布原理，配对联合刺激（PAS）可在M1中产生持久变化。本研究旨在通过将无创经脊髓刺激与经颅磁刺激（TMS）经皮层刺激配对，来确定人类皮层和脊髓神经元回路中的神经生理学变化。我们以精确的刺激间隔进行了40分钟的经脊髓和经皮层配对刺激，TMS在经脊髓刺激之后（经脊髓 - 经皮层PAS）或之前（经皮层 - 经脊髓PAS）施加。经脊髓 - 经皮层PAS显著降低了皮层内抑制，增加了皮层内易化和M1兴奋性，同时运动阈值降低，并减少了比目鱼肌霍夫曼反射（H反射）低频介导的同突触抑制。经皮层 - 经脊髓PAS不影响皮层内回路，降低了M1兴奋性，并减少了比目鱼肌H反射配对刺激脉冲介导的激活后抑制。两种方案均影响Ia类传入纤维和运动轴突的兴奋阈值。这些发现清楚地表明，经脊髓刺激与经皮层刺激的配对基于两个相关输入之间的时间间隔和功能网络相互作用，产生了皮层和脊髓兴奋性变化。这种新的PAS范式可能构成一种具有生理影响的重要神经调节方法，因为它可用于同时改变人类皮层内回路、皮质脊髓神经元和脊髓抑制的兴奋性。
