Smith Andrew T, Williams Adrian L, Singh Krishna D
Department of Psychology, Royal Holloway University of London, Egham, United Kingdom.
Hum Brain Mapp. 2004 Apr;21(4):213-20. doi: 10.1002/hbm.20017.
The positive BOLD (blood oxygen level-dependent) response elicited in human visual cortex by a localized visual stimulus is accompanied by a reduction in the BOLD response in regions of the visual cortex that represent unstimulated locations in the visual field. We have suggested previously that this negative BOLD reflects attention-related suppression of neural activity, but it might also be explained in terms of "blood stealing," i.e., hemodynamic changes that have no neural correlate. We distinguish two possible hemodynamic effects of this type: (1). blood flow reduction caused by locally reduced pressure in vessels that share their blood supply with nearby dilated vessels; and (2). blood flow reduction caused by active constriction of vessels under neural control. The first is ruled out as an explanation of negative BOLD by showing that a visual stimulus that stimulates primary visual cortex in one hemisphere can cause extensive suppression in the other hemisphere i.e., it is not a local phenomenon. Negative BOLD most likely reflects suppression of neural activity, but could also reflect an active blood flow control system.
局部视觉刺激在人类视觉皮层中引发的正向BOLD（血氧水平依赖）反应，伴随着视觉皮层中代表视野中未受刺激位置的区域的BOLD反应降低。我们之前曾提出，这种负向BOLD反映了与注意力相关的神经活动抑制，但它也可能用“血液窃取”来解释，即没有神经关联的血液动力学变化。我们区分了这种类型的两种可能的血液动力学效应：（1）与附近扩张血管共享血液供应的血管局部压力降低导致的血流减少；（2）神经控制下血管的主动收缩导致的血流减少。通过表明刺激一个半球的初级视觉皮层的视觉刺激可在另一个半球引起广泛抑制，即它不是局部现象，排除了第一种情况作为负向BOLD的解释。负向BOLD最有可能反映神经活动的抑制，但也可能反映一个活跃的血流控制系统。
