Kida Ikuhiro, Yamamoto Toru
Division of Oral Functional Science, Graduate School of Dental Medicine, Hokkaido University, Hokkaido, Japan.
Neurosci Res. 2008 Sep;62(1):25-31. doi: 10.1016/j.neures.2008.05.006. Epub 2008 Jul 3.
Understanding the mechanism of coupling between neuronal events and hemodynamic responses is important in non-invasive functional imaging of the brain. The stimulus frequency dependence of hemodynamic responses has been studied using a rat somatosensory cortex model; most results for short stimulus durations reveal peak frequencies at which the hemodynamic response is maximized. However, such peak frequencies have not been observed in studies using blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals with long stimulus durations. To clarify whether the stimulus frequency dependence of BOLD signals depends on the stimulus duration, we measured BOLD signals at 7 T with short- and long-stimulus durations for stimulating rat forepaw at 1-10 Hz using spin-echo echo-planar imaging to enhance changes in activation focus. For both these durations, BOLD signals were significantly higher at stimulus frequencies of 3 or 5 Hz in agreement with the results of previous studies using optical techniques. Our results show that stimulus duration has little influence on the stimulus frequency dependence of BOLD signals in the rat somatosensory model. The discrepant results of most previous fMRI studies using gradient-echo sequence may be ascribed to the difference of imaging to enhance activation focus or draining vein.
了解神经元活动与血液动力学反应之间的耦合机制，对于大脑的无创功能成像至关重要。利用大鼠体感皮层模型，对血液动力学反应的刺激频率依赖性进行了研究；对于短刺激持续时间的大多数结果显示，血液动力学反应最大化时的峰值频率。然而，在使用长刺激持续时间的血氧水平依赖（BOLD）功能磁共振成像（fMRI）信号的研究中，尚未观察到此类峰值频率。为了阐明BOLD信号的刺激频率依赖性是否取决于刺激持续时间，我们使用自旋回波平面成像，在7T下测量了短刺激和长刺激持续时间下的BOLD信号，以增强激活焦点的变化，刺激大鼠前爪的频率为1-10Hz。对于这两种持续时间，与之前使用光学技术的研究结果一致，在3或5Hz的刺激频率下，BOLD信号显著更高。我们的结果表明，在大鼠体感模型中，刺激持续时间对BOLD信号的刺激频率依赖性影响很小。大多数先前使用梯度回波序列的fMRI研究结果存在差异，可能归因于增强激活焦点或引流静脉的成像差异。
