Mayhew S D, Mullinger K J, Ostwald D, Porcaro C, Bowtell R, Bagshaw A P, Francis S T
Birmingham University Imaging Centre (BUIC), School of Psychology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
Birmingham University Imaging Centre (BUIC), School of Psychology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK.
Neuroimage. 2016 Jun;133:62-74. doi: 10.1016/j.neuroimage.2016.02.077. Epub 2016 Mar 5.
In functional magnetic resonance imaging (fMRI), the relationship between positive BOLD responses (PBRs) and negative BOLD responses (NBRs) to stimulation is potentially informative about the balance of excitatory and inhibitory brain responses in sensory cortex. In this study, we performed three separate experiments delivering visual, motor or somatosensory stimulation unilaterally, to one side of the sensory field, to induce PBR and NBR in opposite brain hemispheres. We then assessed the relationship between the evoked amplitudes of contralateral PBR and ipsilateral NBR at the level of both single-trial and average responses. We measure single-trial PBR and NBR peak amplitudes from individual time-courses, and show that they were positively correlated in all experiments. In contrast, in the average response across trials the absolute magnitudes of both PBR and NBR increased with increasing stimulus intensity, resulting in a negative correlation between mean response amplitudes. Subsequent analysis showed that the amplitude of single-trial PBR was positively correlated with the BOLD response across all grey-matter voxels and was not specifically related to the ipsilateral sensory cortical response. We demonstrate that the global component of this single-trial response modulation could be fully explained by voxel-wise vascular reactivity, the BOLD signal standard deviation measured in a separate resting-state scan (resting state fluctuation amplitude, RSFA). However, bilateral positive correlation between PBR and NBR regions remained. We further report that modulations in the global brain fMRI signal cannot fully account for this positive PBR-NBR coupling and conclude that the local sensory network response reflects a combination of superimposed vascular and neuronal signals. More detailed quantification of physiological and noise contributions to the BOLD signal is required to fully understand the trial-by-trial PBR and NBR relationship compared with that of average responses.
在功能磁共振成像（fMRI）中，对刺激的正性血氧水平依赖反应（PBRs）与负性血氧水平依赖反应（NBRs）之间的关系，可能有助于了解感觉皮层中兴奋性和抑制性脑反应的平衡。在本研究中，我们进行了三项独立实验，单侧对感觉野的一侧施加视觉、运动或体感刺激，以在相对的脑半球中诱导PBR和NBR。然后，我们在单次试验和平均反应水平上评估对侧PBR和同侧NBR的诱发幅度之间的关系。我们从个体时间进程中测量单次试验的PBR和NBR峰值幅度，并表明它们在所有实验中均呈正相关。相比之下，在试验的平均反应中，PBR和NBR的绝对幅度均随刺激强度的增加而增加，导致平均反应幅度之间呈负相关。后续分析表明，单次试验PBR的幅度与所有灰质体素的血氧水平依赖反应呈正相关，且与同侧感觉皮层反应无特定关联。我们证明，这种单次试验反应调制的全局成分可以通过体素级血管反应性（在单独的静息状态扫描中测量的血氧水平依赖信号标准差，即静息状态波动幅度，RSFA）得到充分解释。然而，PBR和NBR区域之间仍存在双侧正相关。我们进一步报告，全脑fMRI信号的调制不能完全解释这种正性PBR - NBR耦合，并得出结论，局部感觉网络反应反映了叠加的血管和神经元信号的组合。与平均反应相比，需要更详细地量化对血氧水平依赖信号的生理和噪声贡献，以充分理解逐次试验的PBR和NBR关系。
