Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
Neuroimage. 2012 Feb 1;59(3):2722-32. doi: 10.1016/j.neuroimage.2011.10.037. Epub 2011 Oct 20.
Interpretation of the blood oxygen level dependent (BOLD) response measured using functional magnetic resonance imaging (fMRI) requires an understanding of the underlying neuronal activity. Here we report on a study using both magnetoencephalography (MEG) and BOLD fMRI, to measure the brain's functional response to electrical stimulation of the median nerve in a paired pulse paradigm. Interstimulus Intervals (ISIs) of 0.25, 0.5, 0.75, 1.0, 1.5 and 2.0 s are used to investigate how the MEG detected neural response to a second pulse is affected by that from a preceding pulse and if these MEG modulations are reflected in the BOLD response. We focus on neural oscillatory activity in the β-band (13-30 Hz) and the P35m component of the signal averaged evoked response in the sensorimotor cortex. A spatial separation of β ERD and ERS following each pulse is demonstrated suggesting that these two effects arise from separate neural generators, with ERS exhibiting a closer spatial relationship with the BOLD response. The spatial distribution and extent of BOLD activity were unaffected by ISI, but modulations in peak amplitude and latency were observed. Non-linearities in both induced oscillatory activity ERS and in the signal averaged evoked response are found for ISIs of up to 2s when the signal averaged evoked response has returned to baseline, with the P35m component displaying paired pulse depression effects. The β-band ERS magnitude was modulated by ISI, however the ERD magnitude was not. These results support the assumption that BOLD non-linearity arises not only from a non-linear vascular response to neural activity but also a non-linear neural response to the stimulus with ISI up to 2 s.
使用功能磁共振成像（fMRI）测量血氧水平依赖（BOLD）反应需要了解潜在的神经元活动。在这里，我们报告了一项使用脑磁图（MEG）和 BOLD fMRI 的研究，以测量大脑对正中神经电刺激的功能反应，采用双脉冲范式。使用 0.25、0.5、0.75、1.0、1.5 和 2.0 s 的刺激间间隔（ISIs）来研究 MEG 检测到的对第二个脉冲的神经反应如何受到前一个脉冲的影响，以及这些 MEG 调制是否反映在 BOLD 反应中。我们专注于感觉运动皮层中β波段（13-30 Hz）的神经振荡活动和信号平均诱发反应的 P35m 分量。在每个脉冲后证明了β ERD 和 ERS 的空间分离，表明这两种效应来自于独立的神经发生器，ERS 与 BOLD 反应具有更密切的空间关系。BOLD 活动的空间分布和程度不受 ISI 的影响，但观察到了峰值幅度和潜伏期的调制。当信号平均诱发反应已恢复到基线时，在高达 2 s 的 ISI 下，发现诱导振荡活动 ERS 和信号平均诱发反应中的非线性，其中 P35m 分量显示出双脉冲抑制效应。β 波段 ERS 幅度受 ISI 调制，而 ERD 幅度不受影响。这些结果支持了这样的假设，即 BOLD 非线性不仅来自于对神经元活动的非线性血管反应，而且还来自于对刺激的非线性神经反应，ISIs 可达 2 s。
