Levy, L. M., Henkin, R. I., Lin, C. S., Hutter, A., & Schellinger, D. (1999). Odor memory induces brain activation as measured by functional MRI. Journal of Computer Assisted Tomography, 23, 487-498.

This study used functional magnetic resonance imaging (fMRI) to measure brain activation in response to the imagination of odors in humans. Brain scans were obtained in normal Ss (M = 9; F = 12) using multislice FLASH MRI in response to imagination of banana and peppermint odors and to the actual smells of the corresponding odors of amyl acetate and menthone, respectively. Three coronal sections were selected from anterior to posterior temporal brain regions and observed. Similar measurements were made 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 was present in each section in all normal Ss and in each patient after imagination of each vapor. In normal Ss, brain activation in response to imagination of odors was significantly less than that in response to the actual smell of those 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 in quantitative terms from that before treatment; however, brain activation in response to the actual odor was significantly greater than in imagination. Brain regions activated by both odor imagination and actual corresponding odor were similar and consistent with regions previously described as responding to odors.

Implications.

1. Similar brain regions are activated by both imagined and corresponding actual odors.
2. Imagined odors elicit quantitatively less brain activation than do actual odors in normal Ss.
3. Absolute brain activation by odor imagination in men 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 of men.
4. Once an odor has been experienced, odor imagination, 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.

These findings support the existence of similar brain activation maps between real and imagined experiences.

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