Baker Mark R, Baker Stuart N
Department of Anatomy, University of Cambridge, Cambridge CB2 3DY, UK.
J Physiol. 2003 Feb 1;546(Pt 3):931-42. doi: 10.1113/jphysiol.2002.029553.
EEG recordings from sensorimotor cortex show oscillations around 10 and 20 Hz. These modulate with task performance, and are strongest during periods of steady contraction. The 20 Hz oscillations are coherent with contralateral EMG. Computer modelling suggests that oscillations arising within the cortex may be especially dependent on inhibitory systems. The benzodiazepine diazepam enhances the size of GABA(A) IPSPs; its effects are reversed by the antagonist flumazenil. We tested the effect of these drugs on spectral measures of EEG and EMG, whilst eight healthy human subjects performed a precision grip task containing both holding and movement phases. Either an auxotonic or isometric load was used. EEG changes following electrical stimulation of the contralateral median nerve were also assessed. The EEG power showed similar changes in all task/stimulation protocols used. Power around 20 Hz doubled at the highest dose of diazepam used (5 mg), and returned to control levels following flumazenil. EEG power at 10 Hz was by contrast little altered. The peak frequency of EEG power in both bands was not changed by diazepam. Corticomuscular coherence at ca 20 Hz was reduced following diazepam injection, but the magnitude of this effect was small (mean coherence during steady holding in the auxotonic task was 0.062 in control recordings, 0.051 after 2.5 mg and 5 mg doses of diazepam). These results imply that 20 Hz oscillations in the sensorimotor cortex are at least partially produced by local cortical circuits reliant on GABA(A)-mediated intracortical inhibition, whereas 10 Hz rhythms arise by a different mechanism. Rhythms generated during different tasks, or following nerve stimulation, are likely to arise from similar mechanisms. By examining the formulae used to calculate coherence, we show that if cortical oscillations are simply transmitted to the periphery, corticomuscular coherence should increase in parallel with the ratio of EEG to EMG power. The relative constancy of coherence even when the amplitude of cortical oscillations is perturbed suggests that corticomuscular coherence itself may have a functional role in motor control.
来自感觉运动皮层的脑电图记录显示出频率约为10赫兹和20赫兹的振荡。这些振荡会随着任务表现而调节，并且在稳定收缩期间最为强烈。20赫兹的振荡与对侧肌电图具有相关性。计算机建模表明，皮层内产生的振荡可能特别依赖于抑制系统。苯二氮䓬类药物地西泮会增强GABA(A)抑制性突触后电位的幅度；其作用可被拮抗剂氟马西尼逆转。我们测试了这些药物对脑电图和肌电图频谱测量的影响，同时八名健康人类受试者执行了一项包含握持和运动阶段的精确抓握任务。使用了辅助张力或等长负荷。还评估了对侧正中神经电刺激后的脑电图变化。在所有使用的任务/刺激方案中，脑电图功率显示出相似的变化。在使用的最高剂量地西泮（5毫克）时，20赫兹左右的功率增加了一倍，并在注射氟马西尼后恢复到对照水平。相比之下，10赫兹时的脑电图功率变化很小。地西泮并未改变两个频段脑电图功率的峰值频率。注射地西泮后，约20赫兹的皮质肌电图相关性降低，但这种效应的幅度较小（在辅助张力任务的稳定握持期间，对照记录中的平均相关性为0.062，2.5毫克和5毫克剂量地西泮后为0.051）。这些结果表明，感觉运动皮层中的20赫兹振荡至少部分是由依赖GABA(A)介导的皮质内抑制的局部皮质回路产生的，而10赫兹节律则通过不同的机制产生。在不同任务期间或神经刺激后产生的节律可能由相似的机制产生。通过检查用于计算相关性的公式，我们表明，如果皮质振荡只是简单地传递到外周，皮质肌电图相关性应该与脑电图与肌电图功率的比率平行增加。即使皮质振荡幅度受到干扰，相关性的相对稳定性表明皮质肌电图相关性本身可能在运动控制中具有功能作用。
