Daskalakis Zafiris J, Christensen Bruce K, Fitzgerald Paul B, Roshan Lailoma, Chen Robert
Centre for Addiction and Mental Health, Toronto, Ontario, Canada.
J Physiol. 2002 Aug 15;543(Pt 1):317-26. doi: 10.1113/jphysiol.2002.017673.
Transcranial magnetic stimulation can be used to non-invasively study inhibitory processes in the human motor cortex. Interhemispheric inhibition can be measured by applying a conditioning stimulus to the motor cortex resulting in inhibition of the contralateral motor cortex. Transcranial magnetic stimulation can also be used to demonstrate ipsilateral cortico-cortical inhibition in the motor cortex. At least two different ipsilateral cortico-cortical inhibitory processes have been identified: short interval intracortical inhibition and long interval intracortical inhibition. However, the relationship between interhemispheric inhibition and ipsilateral cortico-cortical inhibition remains unclear. This study examined the relationship between interhemispheric inhibition, short interval intracortical inhibition and long interval intracortical inhibition. First, the effect of test stimulus intensity on each inhibitory process was studied. Second, the effects of interhemispheric inhibition on short interval intracortical inhibition and long interval intracortical inhibition on interhemispheric inhibition were examined. Motor evoked potentials were recorded from the right first dorsal interosseous muscle in 11 right-handed healthy volunteers. For interhemispheric inhibition, conditioning stimuli were applied to the right motor cortex and test stimuli to the left motor cortex. For short interval intracortical inhibition and long interval intracortical inhibition, both conditioning stimuli and test stimuli were applied to the left motor cortex. With increasing test stimulus intensities, long interval intracortical inhibition and interhemispheric inhibition decreased, while short interval intracortical inhibition increased. Moreover, short interval intracortical inhibition was significantly reduced in the presence of interhemispheric inhibition. Interhemispheric inhibition was significantly reduced in the presence of long interval intracortical inhibition when matched for test motor evoked potential amplitude but the difference was not significant when matched for test pulse intensity. These findings suggest that both interhemispheric inhibition and long interval intracortical inhibition are predominately mediated by low threshold cortical neurons and may share common inhibitory mechanisms. In contrast, the mechanisms mediating short interval intracortical inhibition are probably different from those mediating long interval intracortical inhibition and interhemispheric inhibition although these systems appear to interact.
经颅磁刺激可用于非侵入性地研究人类运动皮层的抑制过程。通过对运动皮层施加条件刺激以抑制对侧运动皮层，可测量半球间抑制。经颅磁刺激还可用于证明运动皮层的同侧皮质 - 皮质抑制。至少已识别出两种不同的同侧皮质 - 皮质抑制过程：短间隔皮质内抑制和长间隔皮质内抑制。然而，半球间抑制与同侧皮质 - 皮质抑制之间的关系仍不清楚。本研究考察了半球间抑制、短间隔皮质内抑制和长间隔皮质内抑制之间的关系。首先，研究了测试刺激强度对每种抑制过程的影响。其次，考察了半球间抑制对短间隔皮质内抑制的影响以及长间隔皮质内抑制对半球间抑制的影响。在11名右利手健康志愿者的右侧第一背侧骨间肌记录运动诱发电位。对于半球间抑制，条件刺激施加于右侧运动皮层，测试刺激施加于左侧运动皮层。对于短间隔皮质内抑制和长间隔皮质内抑制，条件刺激和测试刺激均施加于左侧运动皮层。随着测试刺激强度的增加，长间隔皮质内抑制和半球间抑制降低，而短间隔皮质内抑制增加。此外，在存在半球间抑制的情况下，短间隔皮质内抑制显著降低。当测试运动诱发电位幅度匹配时，在存在长间隔皮质内抑制的情况下半球间抑制显著降低，但当测试脉冲强度匹配时差异不显著。这些发现表明，半球间抑制和长间隔皮质内抑制主要由低阈值皮质神经元介导，可能共享共同的抑制机制。相比之下，介导短间隔皮质内抑制的机制可能与介导长间隔皮质内抑制和半球间抑制的机制不同，尽管这些系统似乎相互作用。
