Levy L M, Henkin R I, Lin C S, Hutter A, Schellinger D
Department of Radiology, Georgetown University Medical Center, Washington, DC, USA.
J Comput Assist Tomogr. 1999 Jul-Aug;23(4):487-98. doi: 10.1097/00004728-199907000-00001.
Our goal was to use functional MRI (fMRI) to measure brain activation in response to imagination of odors in humans.
fMR brain scans were obtained in 21 normal subjects (9 men, 12 women) using multislice FLASH MRI in response to imagination of odors of banana and peppermint and to the actual smells of the corresponding odors of amyl acetate and menthone, respectively, in three coronal sections selected from anterior to posterior temporal brain regions. Similar studies were obtained in two patients with hyposmia using FLASH MRI and in one patient with hyposmia using echo planar imaging, both before and after theophylline treatment, which returned smell function to or toward normal in each patient. Activation images were derived using correlation analysis, and ratios of areas of brain activated to total brain areas were calculated.
Activation was present in each section in all normal subjects and in each patient after imagination of each vapor. In normal subjects, brain activation in response to imagination of odors was significantly less than that in response to the actual smell of these odors, and activation following imagination of banana odor was significantly greater in men than in women, as was previously reported for the actual smell of the odor of amyl acetate. However, in relative terms, albeit at an absolute lower brain activation level, the ratio of brain activation by imagination of banana to activation by actual amyl acetate odor was about twice as high in women as in men. Before treatment, in patients with hyposmia, brain activation in response to odor imagination was greater than after presentation of the actual odor itself. After treatment, in patients with hyposmia in whom smell acuity returned to or toward normal, brain activation in response to odor imagination was not significantly different quantitatively from that before treatment; however, brain activation in response to the actual odor was significantly greater than that in response to imagination of the corresponding odor. Brain regions activated by both odor imagination and actual corresponding odor were similar and consistent with regions previously described as responding to odors.
These studies indicate that (a) odors can be imagined and similar brain regions are activated by both imagined and corresponding actual odors; (b) imagination of odors elicits quantitatively less brain activation than do actual smells of corresponding odors in normal subjects; (c) absolute brain activation in men by odor imagination is greater than in women for some odors, but on a relative basis, the ratio for odor imagination to actual smell in women is twice that in men; (d) odor imagination, once the odor has been experienced, is present, recallable, and capable of inducing a relatively constant degree of brain activation even in the absence of the ability to recognize an actual corresponding odor.
我们的目标是使用功能磁共振成像（fMRI）来测量人类在想象气味时大脑的激活情况。
对21名正常受试者（9名男性，12名女性）进行fMR脑扫描，使用多层快速低角度激发（FLASH）磁共振成像，分别在从颞叶脑区前部到后部选取的三个冠状面上，让受试者想象香蕉和薄荷的气味以及闻乙酸戊酯和薄荷酮相应气味的实际嗅觉。对两名嗅觉减退患者在茶碱治疗前后分别使用FLASH磁共振成像进行了类似研究，对一名嗅觉减退患者在茶碱治疗前后使用回波平面成像进行了研究，每名患者的嗅觉功能在治疗后恢复到正常或接近正常。使用相关分析得出激活图像，并计算大脑激活区域与全脑区域的面积比。
在所有正常受试者以及每名患者想象每种气味后，每个脑区都出现了激活。在正常受试者中，想象气味时大脑的激活明显少于闻这些气味的实际嗅觉时的激活，而且正如之前报道乙酸戊酯气味的实际嗅觉那样，男性想象香蕉气味后的激活明显大于女性。然而，相对而言，尽管大脑激活的绝对水平较低，但女性想象香蕉气味时的大脑激活与实际闻乙酸戊酯气味时的大脑激活之比约为男性的两倍。治疗前，嗅觉减退患者想象气味时的大脑激活大于闻实际气味时的大脑激活。治疗后，嗅觉敏锐度恢复到正常或接近正常的嗅觉减退患者，想象气味时的大脑激活在数量上与治疗前没有显著差异；然而，闻实际气味时的大脑激活明显大于想象相应气味时的大脑激活。由气味想象和相应实际气味激活的脑区相似，且与之前描述的对气味有反应的脑区一致。
这些研究表明：（a）气味可以被想象，想象的气味和相应的实际气味会激活相似的脑区；（b）在正常受试者中，想象气味引发的大脑激活在数量上少于相应气味的实际嗅觉引发的大脑激活；（c）对于某些气味，男性由气味想象引起的大脑绝对激活大于女性，但相对而言，女性气味想象与实际嗅觉的激活比是男性的两倍；（d）一旦体验过某种气味后，即使在无法识别相应实际气味的情况下，气味想象也是存在的、可回忆的，并且能够引发相对恒定程度的大脑激活。
