De Carli Diego, Garreffa Girolamo, Colonnese Claudio, Giulietti Giovanni, Labruna Ludovica, Briselli Ennio, Ken Soléakhéna, Macrì Maria Antonietta, Maraviglia Bruno
MARBILab, Enrico Fermi Center, 00184 Rome, Italy.
Magn Reson Imaging. 2007 Jul;25(6):933-8. doi: 10.1016/j.mri.2007.03.031. Epub 2007 May 23.
Functional magnetic resonance imaging (fMRI) techniques are based on the assumption that changes in neural activity are accompanied by modulation in the blood-oxygenation-level-dependent (BOLD) signal. In addition to conventional increases in BOLD signals, sustained negative BOLD signal changes are occasionally observed in many fMRI experiments, which show regions of cortex that seem to respond in antiphase with primary stimulus. The existence of this so-called negative BOLD response (NBR) has been observed and investigated in many functional studies. Several theoretical mechanisms have been proposed to account for it, but its origin has never been fully explained. In this study, the variability of fMRI activation, including the sources of the negative BOLD signal, during phonological and semantic language tasks, was investigated in six right-handed healthy subjects. We found significant activations in the brain regions, mainly in the left hemisphere, involved in the language stimuli [prominent in the inferior frontal gyrus, approximately Brodmann Areas (BA)7, BA44, BA45 and BA47, and in the precuneus]. Moreover, we observed activations in motor regions [precentral gyrus and supplementary motor area (SMA)], a result that suggests a specific role of these areas (particularly the SMA) in language processing. Functional analysis have also shown that certain brain regions, including the posterior cingulate cortex and the anterior cingulate cortex, have consistently greater activity during resting states compared to states of performing cognitive tasks. In our study, we observed diffuse NBR at the cortical level and a stronger negative response in correspondence to the main sinuses. These phenomena seem to be unrelated to a specific neural activity, appearing to be expressions of a mechanical variation in hemodynamics. We discussed about the importance of these responses that are anticorrelated with the stimulus. Our data suggest that particular care must be considered in the interpretation of fMRI findings, especially in the case of presurgical studies.
功能磁共振成像（fMRI）技术基于这样一种假设，即神经活动的变化伴随着血氧水平依赖（BOLD）信号的调制。除了常规的BOLD信号增加外，在许多fMRI实验中偶尔也会观察到持续的负BOLD信号变化，这些变化显示出皮层区域似乎与初级刺激呈反相反应。这种所谓的负BOLD反应（NBR）的存在已在许多功能研究中得到观察和研究。已经提出了几种理论机制来解释它，但其起源从未得到充分解释。在本研究中，我们对6名右利手健康受试者在语音和语义语言任务期间fMRI激活的变异性进行了研究，包括负BOLD信号的来源。我们发现大脑区域有显著激活，主要在左半球，参与语言刺激[在额下回、大致的布罗德曼区（BA）7、BA44、BA45和BA47以及楔前叶中尤为突出]。此外，我们在运动区域[中央前回和辅助运动区（SMA）]观察到激活，这一结果表明这些区域（特别是SMA）在语言处理中具有特定作用。功能分析还表明，与执行认知任务的状态相比，某些脑区，包括后扣带回皮层和前扣带回皮层，在静息状态下始终具有更强的活动。在我们的研究中，我们在皮层水平观察到弥漫性NBR，并且在主要鼻窦对应的区域有更强的负反应。这些现象似乎与特定的神经活动无关，似乎是血液动力学机械变化的表现。我们讨论了这些与刺激呈反相关的反应的重要性。我们的数据表明，在解释fMRI结果时必须特别小心，尤其是在术前研究的情况下。
